Proposed Rule2023-03526
Endangered and Threatened Wildlife and Plants; California Spotted Owl; Endangered Status for the Coastal-Southern California Distinct Population Segment and Threatened Status With Section 4(d) Rule for the Sierra Nevada Distinct Population Segment
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
February 23, 2023
Issuing agencies
Interior DepartmentFish and Wildlife Service
Abstract
We, the U.S. Fish and Wildlife Service (Service), propose to list two distinct population segments (DPSs) of the California spotted owl (Strix occidentalis occidentalis), a bird species from California and Nevada, under the Endangered Species Act of 1973, as amended (Act). This determination also serves as our 12-month finding on a petition to list the California spotted owl. After a review of the best available scientific and commercial information, we find that listing the Coastal-Southern California DPS as endangered is warranted, and that listing the Sierra Nevada DPS as threatened is warranted. Accordingly, we propose to list the Coastal-Southern California DPS as an endangered species under the Act and the Sierra Nevada DPS as a threatened species with a rule issued under section 4(d) of the Act ("4(d) rule"). If we finalize this rule as proposed, it will add these two DPSs to the List of Endangered and Threatened Wildlife and extend the Act's protections to them.
Full Text
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[Federal Register Volume 88, Number 36 (Thursday, February 23, 2023)]
[Proposed Rules]
[Pages 11600-11639]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-03526]
[[Page 11599]]
Vol. 88
Thursday,
No. 36
February 23, 2023
Part IV
Department of the Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; California Spotted Owl;
Endangered Status for the Coastal-Southern California Distinct
Population Segment and Threatened Status With Section 4(d) Rule for the
Sierra Nevada Distinct Population Segment; Proposed Rule
Federal Register / Vol. 88, No. 36 / Thursday, February 23, 2023 /
Proposed Rules
[[Page 11600]]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R8-ES-2022-0166; FF09E21000 FXES1111090FEDR 234]
RIN 1018-BG64
Endangered and Threatened Wildlife and Plants; California Spotted
Owl; Endangered Status for the Coastal-Southern California Distinct
Population Segment and Threatened Status With Section 4(d) Rule for the
Sierra Nevada Distinct Population Segment
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Proposed rule.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to
list two distinct population segments (DPSs) of the California spotted
owl (Strix occidentalis occidentalis), a bird species from California
and Nevada, under the Endangered Species Act of 1973, as amended (Act).
This determination also serves as our 12-month finding on a petition to
list the California spotted owl. After a review of the best available
scientific and commercial information, we find that listing the
Coastal-Southern California DPS as endangered is warranted, and that
listing the Sierra Nevada DPS as threatened is warranted. Accordingly,
we propose to list the Coastal-Southern California DPS as an endangered
species under the Act and the Sierra Nevada DPS as a threatened species
with a rule issued under section 4(d) of the Act (``4(d) rule''). If we
finalize this rule as proposed, it will add these two DPSs to the List
of Endangered and Threatened Wildlife and extend the Act's protections
to them.
DATES: We will accept comments received or postmarked on or before
April 24, 2023. Comments submitted electronically using the Federal
eRulemaking Portal (see ADDRESSES, below) must be received by 11:59
p.m. eastern time on the closing date. We must receive requests for a
public hearing, in writing, at the address shown in FOR FURTHER
INFORMATION CONTACT by April 10, 2023.
ADDRESSES:
Written comments: You may submit comments by one of the following
methods:
(1) Electronically: Go to the Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>. In the Search box, enter FWS-R8-ES-2022-0166,
which is the docket number for this rulemaking. Then, click on the
Search button. On the resulting page, in the panel on the left side of
the screen, under the Document Type heading, check the Proposed Rule
box to locate this document. You may submit a comment by clicking on
``Comment.''
(2) By hard copy: Submit by U.S. mail to: Public Comments
Processing, Attn: FWS-R8-ES-2022-0166, U.S. Fish and Wildlife Service,
MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
We request that you send comments only by the methods described
above. We will post all comments on <a href="https://www.regulations.gov">https://www.regulations.gov</a>. This
generally means that we will post any personal information you provide
us (see Information Requested, below, for more information).
Availability of supporting materials: Supporting materials, such as
the species status assessment report, are available at <a href="https://www.regulations.gov">https://www.regulations.gov</a> under Docket No. FWS-R8-ES-2022-0166.
FOR FURTHER INFORMATION CONTACT: Michael Fris, Field Supervisor,
Sacramento Fish and Wildlife Office, 2800 Cottage Way, Sacramento, CA
95825; telephone 916-414-6700. Individuals in the United States who are
deaf, deafblind, hard of hearing, or have a speech disability may dial
711 (TTY, TDD, or TeleBraille) to access telecommunications relay
services. Individuals outside the United States should use the relay
services offered within their country to make international calls to
the point-of-contact in the United States.
SUPPLEMENTARY INFORMATION:
Executive Summary
Why we need to publish a rule. Under the Act, a species warrants
listing if it meets the definition of an endangered species (in danger
of extinction throughout all or a significant portion of its range) or
a threatened species (likely to become endangered within the
foreseeable future throughout all or a significant portion of its
range). If we determine that a species warrants listing, we must list
the species promptly and designate the species' critical habitat to the
maximum extent prudent and determinable. We have determined that the
Sierra Nevada DPS of the California spotted owl meets the definition of
a threatened species, and the Coastal-Southern California DPS of the
California spotted owl meets the definition of an endangered species;
therefore, we are proposing to list them as such. Listing a species as
an endangered or threatened species can be completed only by issuing a
rule through the Administrative Procedure Act rulemaking process (5
U.S.C. 551 et seq.).
What this document does. We propose the listing of the Sierra
Nevada DPS of the California spotted owl as a threatened species with a
rule under section 4(d) of the Act and the Coastal-Southern California
DPS of the California spotted owl as an endangered species under the
Act.
The basis for our action. Under the Act, we may determine that a
species is an endangered or threatened species because of any of five
factors: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence.
We have determined that both the Sierra Nevada population and the
coastal-southern California population of the California spotted owl
are discrete and significant under our DPS policy and are, therefore,
listable entities under the Act. The Sierra Nevada DPS is found in the
Sierra Nevada Mountain Ranges and foothills in California and western
Nevada. The Coastal-Southern California DPS is found in the Coast,
Transverse, and Peninsular Ranges of California. These two DPSs
together represent the entirety of the California spotted owl's range.
The Sierra Nevada DPS of the California spotted owl is currently
being impacted by high-severity fire, tree mortality, drought, and
barred owls. This DPS still has resiliency throughout its range, and
some areas remain in stable condition; however, we expect the magnitude
of impacts from high-severity fire, tree mortality, drought, climate
change, and other threats to increase into the future. Because the
Sierra Nevada DPS is likely to become in danger of extinction within
the foreseeable future, we propose to list it as threatened.
The Coastal-Southern California DPS has low resiliency, redundancy,
and representation. The entirety of the range of this DPS is at
extremely high risk of fire, and available habitat is fragmented. All
areas of the Coastal-Southern California DPS are currently declining,
and the DPS faces additional threats from tree mortality and drought.
Because the Coastal-Southern California DPS is currently in danger of
extinction, we propose to list it as endangered.
[[Page 11601]]
Information Requested
We intend that any final action resulting from this proposed rule
will be based on the best scientific and commercial data available and
be as accurate and as effective as possible. Therefore, we request
comments or information from other governmental agencies, Native
American Tribes, the scientific community, industry, or any other
interested parties concerning this proposed rule.
We particularly seek comments concerning:
(1) The species' biology, range, and population trends, including:
(a) Biological or ecological requirements of the species, including
habitat requirements for feeding, breeding, and sheltering;
(b) Genetics and taxonomy;
(c) Historical and current range, including distribution patterns
and the locations of any additional populations of this species;
(d) Historical and current population levels, and current and
projected trends; and
(e) Past and ongoing conservation measures for the species, its
habitat, or both.
(2) Factors that may affect the continued existence of the species,
which may include habitat modification or destruction, overutilization,
disease, predation, the inadequacy of existing regulatory mechanisms,
or other natural or manmade factors.
(3) Biological, commercial trade, or other relevant data concerning
any threats (or lack thereof) to this species and existing regulations
that may be addressing those threats.
(4) Additional information concerning the historical and current
status of this species.
(5) Information on regulations that may be necessary and advisable
to provide for the conservation of the Sierra Nevada DPS of the
California spotted owl and that we can consider in developing a 4(d)
rule for the species. In particular, information concerning the extent
to which we should include any of the section 9 prohibitions in the
4(d) rule or whether we should consider any additional exceptions from
the prohibitions in the 4(d) rule.
(6) Whether we should include in our 4(d) rule for the Sierra
Nevada DPS the provision at 50 CFR 17.7 for raptors in captivity.
(7) Which areas may be appropriate as critical habitat for the
species and why areas should or should not be proposed for designation
as critical habitat in the future, including whether there are threats
to the species from human activity that would be expected to increase
due to the designation and whether that increase in threat would
outweigh the benefit of designation such that the designation of
critical habitat may not be prudent.
(8) Specific information on:
(a) The amount and distribution of habitat for the Sierra Nevada
DPS and the Coastal-Southern California DPS of the California spotted
owl which should be considered for proposed critical habitat;
(b) What may constitute the physical or biological features
essential to the conservation of the species within the geographical
range currently occupied by the species;
(c) Where these features are currently found;
(d) Whether any of these features may require special management
considerations or protection;
(e) What areas are currently occupied and contain features
essential to the conservation of the species that should be included in
the designation and why; and
(f) What unoccupied areas may be essential for the conservation of
the species and why.
Please include sufficient information, such as scientific journal
articles or other publications, to allow us to verify any scientific or
commercial information you include.
Please note that submissions merely stating support for, or
opposition to, the action under consideration without providing
supporting information, although noted, do not provide substantial
information necessary to support a determination. Section 4(b)(1)(A) of
the Act (16 U.S.C. 1533(b)(1)(A)) directs that determinations as to
whether any species is an endangered or a threatened species must be
made solely on the basis of the best scientific and commercial data
available.
You may submit your comments and materials concerning this proposed
rule by one of the methods listed in ADDRESSES. We request that you
send comments only by the methods described in ADDRESSES.
If you submit information via <a href="https://www.regulations.gov">https://www.regulations.gov</a>, your
entire submission--including any personal identifying information--will
be posted on the website. If your submission is made via a hardcopy
that includes personal identifying information, you may request at the
top of your document that we withhold this information from public
review. However, we cannot guarantee that we will be able to do so. We
will post all hardcopy submissions on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Comments and materials we receive, as well as supporting
documentation we used in preparing this proposed rule, will be
available for public inspection on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Because we will consider all comments and information we receive
during the comment period, our final determinations may differ from
this proposal. Based on the new information we receive (and any
comments on that new information), we may conclude that the Coastal-
Southern California DPS is threatened instead of endangered, or that
the Sierra Nevada DPS is endangered instead of threatened, or we may
conclude that neither DPS warrants listing as either an endangered
species or a threatened species. In addition, we may change the
parameters of the prohibitions or the exceptions to those prohibitions
in the 4(d) rule for the Sierra Nevada DPS if we conclude it is
appropriate in light of comments and new information received. For
example, we may expand the incidental-take prohibitions or the
exceptions to those prohibitions in the 4(d) rule for the Sierra Nevada
DPS to include prohibiting additional activities if we conclude that
those additional activities are not compatible with conservation of the
DPS. Conversely, we may establish additional exceptions to the
incidental-take prohibitions in the final rule if we conclude that the
activities would facilitate or are compatible with the conservation and
recovery of the DPS.
Public Hearing
Section 4(b)(5) of the Act (16 U.S.C. 1533(b)(5)) provides for a
public hearing on this proposal, if requested. Requests must be
received by the date specified in DATES. Such requests must be sent to
the address shown in FOR FURTHER INFORMATION CONTACT. We will schedule
a public hearing on this proposal, if requested, and announce the date,
time, and place of the hearing, as well as how to obtain reasonable
accommodations, in the Federal Register and local newspapers at least
15 days before the hearing. We may hold the public hearing in person or
virtually via webinar. We will announce any public hearing on our
website, in addition to the Federal Register. The use of virtual public
hearings is consistent with our regulations at 50 CFR 424.16(c)(3).
List of Abbreviations and Acronyms
We use many abbreviations and acronyms in this proposed rule. For
the convenience of the reader, we define some of them here:
ac = acres
BLM = Bureau of Land Management
[[Page 11602]]
CAL FIRE = California Department of Forestry and Fire Protection
CDWR = California Department of Water Resources
CI = confidence interval
cm = centimeters
dbh = diameter at breast height
DPS = distinct population segment
ft = feet
HCP = habitat conservation plan
ha = hectares
in = inches
km = kilometers
IPCC = Intergovernmental Panel on Climate Change
m = meters
mi = miles
MOU = memorandum of understanding
NPS = National Park Service
PAC = protected activity center
RCP = representative concentration pathway
SPI = Sierra Pacific Industries
SSA = species status assessment
USFS = U.S. Forest Service
Previous Federal Actions
For a detailed history of prior petitions, listing actions, and
litigation, please see the 12-month finding published on May 24, 2006
(71 FR 29886). Subsequent to that finding, we were petitioned twice to
list the California spotted owl as endangered or threatened and to
designate its critical habitat under the Act (16 U.S.C. 1531 et seq.).
The first petition was submitted in December 2014, by the Wild Nature
Institute and John Muir Project of Earth Island Institute, and the
second in August 2015, by Sierra Forest Legacy and Defenders of
Wildlife. On September 18, 2015, we published a 90-day finding that the
petitions presented substantial scientific or commercial information
indicating that listing may be warranted for the California spotted owl
(80 FR 56423). On November 8, 2019, we published a 12-month finding
that listing the California spotted owl was not warranted at that time
(84 FR 60371).
In August 2020, Sierra Forest Legacy, Defenders of Wildlife, and
the Center for Biological Diversity filed a complaint challenging our
12-month not-warranted finding. By stipulated settlement agreement
approved by the court on November 30, 2021, we agreed to submit to the
Federal Register a new 12-month finding for the California spotted owl
on or before February 15, 2023 (Sierra Forest Legacy, et al. v. U.S.
Fish and Wildlife Service, et al., No. 5:20-cv-05800-BLF (N.D. Cal.)).
This document serves as our 12-month finding and completes our
obligations under that settlement agreement.
Peer Review
In 2022, a species status assessment (SSA) team prepared an SSA
report for the California spotted owl. The SSA team was composed of
Service biologists, in consultation with other species experts. The SSA
report represents a compilation of the best scientific and commercial
data available concerning the status of the species, including the
impacts of past, present, and future factors (both negative and
beneficial) affecting the species.
In accordance with our joint policy on peer review published in the
Federal Register on July 1, 1994 (59 FR 34270), and our August 22,
2016, memorandum updating and clarifying the role of peer review of
listing actions under the Act, we solicited independent scientific
review of the information contained in the California spotted owl SSA
report. The Service sent the SSA report to four independent peer
reviewers and received one response. Results of this structured peer
review process can be found at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. In
preparing this proposed rule, we incorporated the results of these
reviews, as appropriate, into the SSA report, which is the foundation
for this proposed rule.
Summary of Peer Reviewer Comments
We received comments from one peer reviewer on the draft SSA
report. We reviewed all comments we received from the peer reviewer for
substantive issues and new information regarding the information
contained in the SSA report. The peer reviewer generally provided
additional references, clarifications, and suggestions, including
further definitions of some of the terms used. We updated the SSA
report based on the peer reviewer's comments, including changing the
approach to our scoring system for the current and future habitat
analyses, clarifying specific points where appropriate, and adding
additional details and suggested references where needed. Peer reviewer
comments are addressed in the following summary and were incorporated
into the SSA report as appropriate.
Comment 1: The peer reviewer stated that there was not enough
discussion in the SSA report about how habitat factors have been
observed to impact owls, particularly in regards to the existing
studies analyzing demographic trends of California spotted owls.
Further, the peer reviewer stated that the SSA report should discuss
the methodology used in the demography studies.
Our response: We acknowledge that habitat factors and demographic
factors are interrelated, and that understanding the relation between
those two issues is crucial. We discuss how habitat factors influence
demographic factors, and vice versa, in sections 3.1 and 3.2 of the SSA
report (Service 2022, pp. 14-24). We have also incorporated all
available information on how the two are related. Additionally, not all
of the demographic studies discuss the relationship between vital rates
or population trends and habitat factors, but we incorporated the
information into the SSA report where available.
Regarding the methodology used in the demography studies, we added
a paragraph to the SSA report that discusses different methodologies
used in the different types of population studies available in the
literature (Service 2022, p. 24). We will provide a list of all
literature cited should any readers wish to review those studies in
more detail, and we will provide any studies not readily available on
<a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Comment 2: The peer reviewer further questioned the assumption in
the SSA report that high-quality habitat is equivalent to population
stability, or vice versa.
Our response: While we recognize that data are limited, the best
available scientific and commercial data, including all available
information on habitat use and species needs for the California spotted
owl, concluded that the relationship between high-quality habitat and
population stability is sufficiently certain to rely upon for our
analysis of species viability.
Comment 3: While recognizing that some protected activity center
(PAC) information is out of date, the peer reviewer suggested adding
the amount of PAC area to the analysis units in section 5.3 of the SSA
report.
Our response: The detailed analysis unit descriptions describe the
current condition of each unit. Because PAC information does not
provide insight on the current condition of each analysis unit, it
would not be appropriate to include in section 5.3 of the SSA report (a
PAC is a designation made by the USFS to protect the best available 121
ha (300 ac) of habitat in as compact of a unit as possible around a
nest tree). We do, however, incorporate information from PACs
throughout the SSA report and this proposed rule to understand the
impact, breadth, and distribution of threats across the landscape.
Comment 4: The peer reviewer questioned whether we should use the
same criteria to analyze conditions in the Sierra Nevada and in
coastal/southern California.
Our response: In order to present a standardized comparison across
all analysis units, we used the same scoring criteria for the Sierra
Nevada and
[[Page 11603]]
coastal/southern California. However, we recognize that California
spotted owls may use different-sized trees in the coastal-southern
California population than in the Sierra Nevada population. We
presented a separate analysis acknowledging this, and we included the
difference in tree sizes found in the two geographic areas (Service
2022, tables 9, 13, and 18).
I. Proposed Listing Determination
Background
A thorough review of the taxonomy, life history, and ecology of the
California spotted owl (Strix occidentalis occidentalis) is presented
in the SSA report (version 2.0; Service 2022, pp. 8-14).
California spotted owls are medium-sized brown owls measuring 46.6-
48.3 cm (18.3-19.0 in) with a mottled appearance, round face, large
pale brown facial disks, dark brown eyes, and a yellowish green bill
(Verner et al. 1992, p. 55; Guti[eacute]rrez et al. 2020,
``Appearance'' section). Females are generally slightly larger than
males (Verner et al. 1992, p. 55).
The American Ornithological Society (formerly the American
Ornithologists' Union (AOU)) currently recognizes three distinct
subspecies of spotted owls: northern spotted owl (Strix occidentalis
caurina), California spotted owl, and Mexican spotted owl (Strix
occidentalis lucida) (AOU 1957). Given similarities between the
subspecies of spotted owls, the SSA report and this proposed rule use
available relevant literature for both the northern spotted owl and the
Mexican spotted owl as necessary and appropriate and clearly identify
when we refer to those entities. The term ``spotted owl'' is used when
talking about Strix occidentalis as a whole. Additionally, under the
Act, the term ``species'' includes any subspecies of fish or wildlife
or plants. For the purposes of this proposed rule, we in general use
``species'' to refer to the California spotted owl rather than
``subspecies.''
There is some overlap in range between northern spotted owls and
the California spotted owl, and interbreeding between the two
subspecies occasionally occurs (Haig et al. 2004, p. 690; Barrowclough
et al. 2011, pp. 581, 583-586; Miller et al. 2017, pp. 6871, 6875-6877;
Hanna et al. 2018, pp. 3947-3948, 3950-3951). California spotted owls
have the lowest genetic diversity among the subspecies compared to
northern and Mexican spotted owls, suggesting that the California
spotted owl is of more recent origin than the other spotted owl
subspecies or that populations of the California spotted owl are much
smaller than the northern and Mexican spotted owl populations
(Barrowclough et al. 1999, pp. 919, 927; Haig et al. 2004, p. 683).
Within the California spotted owl, genetic differences between
individuals found in the Sierra Nevada and individuals found in
mountain ranges throughout southern California suggest limited
interbreeding between these two areas (Barrowclough et al. 2005, pp.
1113-1114; Hanna et al. 2018, pp. 3947-3948, 3950). However, these
genetic studies are limited by sample size and sampling locations. We
are only aware of one study that includes California spotted owls from
coastal California; this study shows gene flow between geographically
adjacent spotted owl samples, with some evidence of asymmetrical gene
flow between California spotted owls in Carmel, California (coastal
California), and the Sierra Nevada (Barrowclough et al. 2005, p. 1114).
California spotted owls are distributed across habitat in
California and Nevada including the Sierra Nevada, coastal California,
and southern California. The California spotted owl has also been
documented in the Sierra San Pedro Martir mountains in Baja California
Norte, Mexico, with a few scattered records of the spotted owl in Baja
California between 1887 and 1972 (Grinnell 1928, p. 242; Wilbur 1987,
p. 170). However, many researchers now question whether the species
ever actually occurred in Baja California (Erickson in litt. 2022;
Unitt in litt. 2022). There are only a few accounts of the species,
with none of those accounts mentioning breeding or evidence of breeding
pairs. Therefore, we consider the California spotted owl to be only a
rare visitor of Mexico, and do not consider Baja California as its own
population.
California spotted owls are continuously distributed throughout the
forests of the western side of the Sierra Nevada from Shasta County
south to the Tehachapi Pass in Kern County (Guti[eacute]rrez et al.
2017, pp. 13-14). They are sparsely distributed on the eastern side of
the Sierra Nevada into western Nevada (GBBO 2012, p. Spp-47-4). Outside
of the Sierra Nevada, the species' range is not contiguous. Along the
California coast and into southern California, the species is found in
the Coast, Transverse, and Peninsular mountain ranges from Monterey
County in the north to San Diego County in the south (Guti[eacute]rrez
et al. 2020, ``Distribution'' section). However, there is a large break
in the species' range around San Luis Obispo County, where the species
is not known to occur. The Tehachapi Pass between the Sierra Nevada to
the east and the Transverse Range to the west represents a gap between
California spotted owls in the Sierra Nevada and California spotted
owls in coastal and southern California (Verner et al. 1992, p. 4).
California spotted owls are absent from the Santa Cruz Mountains (part
of the Coast Range) in California, where suitable habitat appears to be
present (Guti[eacute]rrez et al. 2017, p. 240).
California spotted owls are currently found throughout their known
historical range, although there is evidence of a decrease in abundance
in parts of the range including both the Sierra Nevada and southern
California (Franklin et al. 2004, pp. 23-42; Tempel et al. 2014b, pp.
90-94; Conner et al. 2016, pp. 7-18; Hanna et al. 2018, pp. 3947-3949;
Tempel et al. 2022, p. 18). The majority of California spotted owls are
found in mid-elevation, mixed-conifer forest on the west slope of the
Sierra Nevada (Guti[eacute]rrez et al. 2017, p. xviii).
California spotted owls are long-lived (approximately 16-23 years)
with high adult survival and low reproductive output (Seamans and
Guti[eacute]rrez 2007, p. 57; Guti[eacute]rrez et al. 2020,
``Demography and Populations'' section). Pairs exhibit high territory
fidelity (Guti[eacute]rrez et al. 2020, ``Sounds and Vocal Behavior''
and ``Behavior'' sections). Territories--the area actively defended by
a breeding pair--can overlap with neighboring pairs and are smaller
than home ranges (Guti[eacute]rrez et al. 2017, pp. xvi, 294).
Estimates of territory size have varied from 203 ha (502 ac) to 813 ha
(2,009 ac), with higher estimates in the northern Sierra Nevada and
lower estimates in southern California (Bingham and Noon 1997, p. 136;
Blakesley et al. 2005, p. 1556; Seamans and Guti[eacute]rrez 2007b, p.
568; Tempel et al. 2014b, p. 2091). Higher quality territories measured
in adult survival, territory colonization, and territory extinction,
tend to have a greater proportion of higher canopy cover (Tempel et al.
2014b, p. 2089; Guti[eacute]rrez et al. 2017, pp. 271-273). Home
ranges, or areas used by a pair to meet requirements for survival and
reproduction, are about 400-1,200 hectares (ha) (1,000-3,000 acres
(ac)) in size (Guti[eacute]rrez et al. 2017, p. xviii). Home ranges are
typically larger in the northern portion of the range (>1,000 ha (2,470
ac)) and smaller in the southern portion of the range (<1,000 ha (2,470
ac)) due to differences in selected prey species (Guti[eacute]rrez et
al. 2017, p. xviii).
Breeding season begins in mid-February, and the juvenile dependency
period can last through mid-September;
[[Page 11604]]
nesting generally starts earlier at lower elevations (Guti[eacute]rrez
et al. 2020, ``Breeding'' section). During the breeding season,
California spotted owls tend to spend the majority of their time at
activity centers of around 121 ha (299 ac) (Verner et al. 1992, p. 87;
Berigan et al. 2012, p. 299). Activity centers are the areas where
California spotted owls they nest, roost, and forage (Verner et al.
1992, p. 87; Guti[eacute]rrez et al. 2017, pp. 270-271). Spotted owls
typically have only one nest per breeding season, and they rarely re-
nest if the first nests fails (Guti[eacute]rrez et al. 2020,
``Breeding'' section). Females typically lay 1-3 eggs, with survival of
offspring into adulthood highest when two young fledge in comparison to
singletons and triplets (Peery and Guti[eacute]rrez 2013, p. 132;
Guti[eacute]rrez et al. 2020, ``Demography and Populations'' section).
Although difficult to estimate due to dispersal, juvenile survival in
California spotted owls is low (Blakesley et al. 2001, p. 667; LaHaye
et al. 2004, p. 1056).
Spotted owls always disperse from their natal areas in the year
they hatch. Natal dispersal occurs during the fall, after juveniles
have reached adult weight and parental care stops (Guti[eacute]rrez et
al. 2020, ``Breeding'' section). Average juvenile dispersal in southern
California is 9.7-11.3 km (6-7 mi), and ranges from 3.2-37.0 km (2-23
mi) (LaHaye et al. 2001, p. 691). Larger dispersal distances, up to 177
km (110 mi), have been documented in both northern and Mexican
subspecies (Guti[eacute]rrez and Carey 1985, p. 60; Ganey et al. 1998,
p. 206; Hollenbeck et al. 2018, p. 533). Adult California spotted owls
typically do not shift territories or undergo breeding dispersal from
an established territory (Blakesley et al. 2006, p. 76; Zimmerman et
al. 2007, p. 963; Guti[eacute]rrez et al. 2011, p. 592); however, some
breeding dispersal occurs in adults or pairs that have been
unsuccessful in mating or if habitat is altered (Blakesley et al. 2006,
p. 71).
Breeding only occurs once a pair is formed and settled into a
territory (Guti[eacute]rrez et al. 2017, p. 15). Pairs can breed in
consecutive years, but in certain conditions may postpone reproduction
until temporarily poor environmental conditions improve (Stearns 1976,
pp. 4, 15-26; Franklin et al. 2000, p. 539; Guti[eacute]rrez et al.
2017, p. xvi). The number of young fledged annually per territorial
California spotted owl female in several areas within the Sierra Nevada
ranged from 0.478-0.988 (Blakesley et al. 2010, pp. 1, 18).
In general, California spotted owls nest in areas of mature,
multistoried forests with complex structure, larger trees, multi-
layered high canopy cover, and large amounts of coarse woody debris,
while areas with higher heterogeneity of forest types and the edges
between them are important for foraging (Guti[eacute]rrez et al. 2017,
p. xvii). In the Sierra Nevada, a majority of California spotted owls
occur within mid-elevation ponderosa pine (Pinus ponderosa), mixed-
conifer, white fir (Abies concolor), and mixed-evergreen forest types,
with few occurring in the lower elevation oak woodlands of the western
foothills (Guti[eacute]rrez et al. 2017, p. 109). In coastal and
southern California, California spotted owls are found in riparian/
hardwood forests and woodlands, live oak/big cone fir forests, and
redwood/California laurel forests (Guti[eacute]rrez et al. 2017, p.
xxvi). In southern California, vegetation types differ relative to the
Sierra Nevada, and what is considered a large tree in southern
California may not be comparable to what is considered a large tree in
the Sierra Nevada. However, California spotted owls in southern
California still select for territories containing larger trees (LaHaye
et al. 1997, pp. 42, 47) and predominantly closed canopy cover (Smith
et al. 2002, pp. 137, 142, 144).
California spotted owls can use a variety of habitat types for
nesting. At higher elevations, the species primarily uses conifers, and
as elevations decrease, they increasingly use hardwoods
(Guti[eacute]rrez et al. 2020, ``Habitat'' section). Important
components of nesting habitat include high canopy cover, larger trees,
and high habitat heterogeneity. For nest trees, California spotted owls
use a subset of larger trees or snags, with the average nest tree
measuring 124 cm (49 in) diameter at breast height (dbh) and 31 m (103
ft) tall in the Sierra Nevada (Guti[eacute]rrez et al. 2017, p. 50). In
southern California, California spotted owls use cavity, broken-top,
and platform nests with different characteristics (LaHaye et al. 1997,
pp. 42, 47; Tanner 2022, pers. comm.). In southern California,
California spotted owl use of platform or old raptor nests is more
common; thus, owls with these types of nests were observed using
smaller trees than used in other nest types (LaHaye et al. 1997, p.
45). Within their nesting territory, California spotted owls select for
nest sites farther away from the forest edge (Phillips et al. 2010, p.
312). Overall, California spotted owl occupancy, colonization, adult
survival, and reproductive success are all positively associated with
an increasing amount of structurally complex habitat on the landscape
(Franklin et al. 2000, p. 578; Blakesley et al. 2005, p. 1562; Tempel
et al. 2014a, pp. 2103-2104).
California spotted owls can also use a variety of habitats to
forage. California spotted owls primarily prey upon a variety of small
to medium-sized mammals, including, but not limited to, flying
squirrels, woodrats, and pocket gophers, as well as birds, lizards, and
insects (Guti[eacute]rrez et al. 2017, p. 28). In the Sierra Nevada,
above approximately 1,200 m (3,937 ft) in coniferous forests,
California spotted owls most commonly consume Humboldt's flying
squirrels (Glaucomys oregonensis) (Laymon 1988, pp. 130-154; Verner et
al. 1992, pp. 4, 65-69; Munton et al. 2002, pp. 99, 101-104). Preferred
habitat conditions of Humboldt's flying squirrels include cool, moist,
mature forest with abundant standing and down snags where they can
forage on mostly fungi and lichens (Cassola 2016, p. 3). In lower
elevation oak woodlands and riparian-deciduous forests in the Sierra
Nevada and southern California, California spotted owls select for
woodrats (Neotoma spp.) (Verner et al. 1992, pp. 4, 65, 68-69; Smith et
al. 1999, pp. 22, 24-28; Munton et al. 2002, pp. 99, 101-104). Due to
this elevational gradient in prey distribution, California spotted owls
select foraging sites characteristic of flying squirrel habitats at
higher elevations and woodrat habitats at lower elevations (Kramer et
al. 2021b, pp. 12-14). Some individuals have smaller home ranges where
woodrats are the primary prey source, presumably because woodrats have
a higher caloric gain per successful foraging event and are found in
higher densities than northern flying squirrels (Zabel et al. 1995, pp.
433, 435-438). There is some evidence that California spotted owl diet
may shift following wildfires. In national parks in the Sierra Nevada
that have implemented longstanding fire management efforts (i.e.,
prescribed fire and managed wildfire), the California spotted owl diet
contains a higher proportion of woodrats and pocket gophers relative to
flying squirrels (Hobart et al. 2021, pp. 254, 256).
In regard to foraging habitat, important components include the
presence of larger trees, high canopy cover, and coarse woody debris.
California spotted owls tend to forage in larger trees, likely due to
the canopy cover provided by larger trees and the important resources
such as shelter and food that larger trees provide for prey species
(Laymon 1988, pp. 47, 71, 77, 100; Verner et al. 1992, pp. 9-10, 60,
88; Moen and Guti[eacute]rrez 1997, pp. 1281, 1284). However,
California spotted owls use medium-size trees (defined by the authors
as >25 cm dbh (9 in)) for
[[Page 11605]]
foraging while avoiding areas dominated by small trees (<25 cm dbh (9
in)) (Kramer et al. 2021a, pp. 4, 6). Coarse woody debris is also an
important habitat feature for California spotted owls because it
provides food, shelter, and protection for prey species, especially
woodrats (Waters and Zabel 1995, pp. 861-862; Pyare and Longland 2002,
pp. 1016-1017; Innes et al. 2007, pp. 1523, 1526; Kelt et al. 2013, p.
1208). Heterogeneous forests, such as those found on private lands, may
provide more habitat for California spotted owls than was previously
understood (Atuo et al. 2019, p. 295), as some privately owned study
areas have higher numbers of occupied sites than adjacent USFS study
areas (Roberts et al. 2017, p. 113).
California spotted owl roosting habitat is very similar to nesting
habitat. Specific components of roosting habitat include multi-layered
high canopy cover and presence of large trees. It is believed that such
forests provide young California spotted owls with protection from
predators and from high temperatures. California spotted owls have a
low heat tolerance in comparison to other bird species, beginning to
show heat stress at 30-34 degrees Celsius ([deg]C) (86-93 degrees
Fahrenheit ([deg]F)). The cooler microclimates that multi-layered high
canopy cover provides are important for both juveniles and adults
during warm summers (Weathers 1981, pp. 358-359; Barrows 1981, pp. 303-
305; Weathers et al. 2001, pp. 678-679). Presence of large trees is
also important for California spotted owl roosting, as individuals tend
to roost in large trees, likely due to the canopy cover provided by
large trees and the resources they provide for prey species (Laymon
1988, pp. 47, 71, 77, 100; Verner et al. 1992, pp. 9-10, 60, 88; Moen
and Guti[eacute]rrez 1997, pp. 1281-1284).
Within the SSA report and this proposed rule, we define a
population as a group of interbreeding California spotted owls that are
more likely to breed among that group than outside of that group. We
use information from genetic studies and habitat features to identify
two California spotted owl populations: one in the Sierra Nevada, and
another in coastal and southern California (hereafter referred to as
the coastal-southern California population).
In the western Sierra Nevada, habitat is relatively continuous,
without significant gaps in distribution (Guti[eacute]rrez et al. 2017,
p. xviii); however, in the eastern Sierra Nevada, habitat is more
discontinuous with disjunct patches (Dilts 2022, pp. 5-9). Despite this
fragmentation, California spotted owls still have substantial gene flow
within the Sierra Nevada. However, there is limited gene flow to
coastal or southern California, and large-scale fragmentation of
suitable habitat divides the Sierra Nevada from this other population
(Barrowclough et al. 2005, pp. 1114-1116). We are not aware of specific
information about individual California spotted owls moving between
these two population areas.
In coastal and southern California, the California spotted owl
population consists of subpopulations distributed among discrete
mountain ranges, resulting in habitat ``islands'' surrounded by
unsuitable habitat (Verner et al. 1992, p. 187). Areas between these
habitat islands are typically lowland desert scrub and chaparral that
is unsuitable for California spotted owls, or substantially modified by
human-induced development and fragmentation (Verner et al. 1992, p.
187). Some of the subpopulations are separated by relatively narrow
gaps, such as the gap between the San Gabriel and San Bernardino
Mountains, while other gaps are more significant, such as the gap
between the Northern and Southern Santa Lucia Mountains. California
spotted owls in coastal and southern California are less well-studied
than those in the Sierra Nevada, but there is a notable lack of
documented California spotted owl movement between the coastal and
southern subpopulations, and we are not aware of any dispersal between
them. This population is also described in the literature as being a
presumed metapopulation (Verner et al. 1992, pp. 187-206; LaHaye et al.
1994, entire; Guti[eacute]rrez et al. 2017, p. 241) despite the
documented lack of connectivity, even though dispersal among
populations is a defining characteristic of a metapopulation (see
Hanski and Gilpin 1991 for more on metapopulation theory). However,
spatial structure of a metapopulation within and among subpopulations
is critical for metapopulation functioning, and available evidence does
not document successful dispersal between the San Bernardino, San
Gabriel, and San Jacinto Mountains, which are adjacent mountain ranges,
indicating that if mixing does occur it is very rare (LaHaye et al.
2001, entire; LaHaye et al. 2004, entire; Guti[eacute]rrez et al. 2017,
pp. 242, 250). Further, not all subpopulations within the
metapopulation have equal likelihood of ``blinking out'' or being
rescued/recolonized by other subpopulations, which are important
components of metapopulation theory (Guti[eacute]rrez et al. 2017, pp.
241-242, 250). Within the coastal-southern California population, the
subpopulation inhabiting the San Bernardino and San Gabriel mountains
is the largest subpopulation and is the subject of most ecological
studies. The persistence of this subpopulation has been identified as
important for persistence of the coastal-southern California population
(Verner et al. 1992, pp. 197-206).
To conduct a more focused analysis of how different portions of
each of the populations' ranges contribute to that population's overall
resiliency, we further divided the Sierra Nevada and southern
California populations into analysis units (see figure 1, below). We
chose analysis units roughly based on public land management boundaries
because of varying demographic data and management strategies across
the range. Dividing the population up into analysis units based on land
management boundaries allows a better assessment of the varying
conditions across the range. We identified a total of 15 analysis
units: Lassen, Plumas, Tahoe, Eldorado, Humboldt-Toiyabe, Stanislaus,
Yosemite, Sierra, Sequoia-Kings Canyon, Sequoia, Inyo, Las Padres, Las
Padres-Angeles, San Bernardino, and Cleveland.
BILLING CODE 4333-15-P
[[Page 11606]]
[GRAPHIC] [TIFF OMITTED] TP23FE23.008
Figure 1--Populations and Analysis Units of the California Spotted Owl
(CSO)
BILLING CODE 4333-15-C
Distinct Population Segment Evaluation
Under the Act, the term ``species'' includes any subspecies of fish
or wildlife or plants, and any distinct population segment of any
species of vertebrate fish or wildlife which interbreeds when mature
(16 U.S.C. 1532(16)). To guide the implementation of the DPS provisions
of the Act, we and the National Marine Fisheries Service (National
Oceanic and Atmospheric Administration--Fisheries), published the
Policy Regarding the Recognition of Distinct Vertebrate Population
Segments Under the Endangered Species Act (DPS Policy) in the Federal
Register on February 7, 1996 (61 FR 4722). Under our DPS Policy, we use
two elements to assess whether a population segment under consideration
for listing may be recognized as a DPS: (1) The population segment's
discreteness from the remainder of the species to which it belongs, and
(2) the significance of the population segment to the species to which
it belongs. If we determine that a population segment being considered
for listing is a DPS, then the population
[[Page 11607]]
segment's conservation status is evaluated based on the five listing
factors established by the Act to determine if listing it as either
endangered or threatened is warranted.
As discussed above in Previous Federal Actions, we were petitioned
to list the California spotted owl subspecies throughout its range. In
response to the petitions, we divided the species into two populations
and our analysis covers the full range of the species. Under the Act,
we have the authority to consider for listing any species, subspecies,
or, for vertebrates, any distinct populations segment of these taxa if
there is sufficient information to indicate that such action may be
warranted. Therefore, we considered whether the two populations of the
California spotted owl (the Sierra Nevada portion of the California
spotted owl's range, and the coastal and southern California portions
of the California spotted owl's range) meet the DPS criteria under the
Act. These two populations comprise the entirety of the California
spotted owl's range (and thus the entirety of the petitioned entity),
and we have determined that it is appropriate to analyze them
individually under our DPS policy.
Discreteness
Under our DPS Policy, a population segment of a vertebrate taxon
may be considered discrete if it satisfies either of the following
conditions: (1) It is markedly separated from other populations of the
same taxon as a consequence of physical, physiological, ecological, or
behavioral factors. Quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation; or (2) it is
delimited by international governmental boundaries within which
differences in control of exploitation, management of habitat,
conservation status, or regulatory mechanisms exist that are
significant in light of section 4(a)(1)(D) of the Act.
We conclude the two segments satisfy the ``markedly separate''
condition. The Sierra Nevada part of the range is separated from the
coastal and southern California parts of the range by large-scale
fragmentation of suitable habitat, with the Tehachapi Pass in Kern
County identified as the dividing line between these areas (Verner et
al. 1992, p. 4; Barrowclough et al. 2005, pp. 1114-1116). The distance
between suitable habitat in the closest parts of the Sierra Nevada and
the Transverse Range of southern California is only 40 km (25 mi).
Although this distance is near the known average dispersal of juvenile
California spotted owls, we are not aware of specific information about
individual California spotted owls moving between the Sierra Nevada and
California spotted owl habitat in coastal and southern California
(Service 2022, p. 18).
As discussed above in Background, there are few genetic studies on
the California spotted owl. However, existing analyses provide evidence
that gene flow between the two parts of the range is limited and may
have been restricted to historical asymmetrical gene flow from areas in
the central California coast to the Sierra Nevada (Barrowclough et al.
2005, p. 1113), although the study acknowledges that more data are
needed to inform this conclusion. Our DPS policy notes that we do not
consider it appropriate to require absolute reproductive isolation as a
prerequisite to recognizing a distinct population segment. As the
policy states, this would be an impracticably stringent standard, and
one that would not be satisfied even by some recognized species that
are known to sustain a low frequency of interbreeding with related
species.
Therefore, because the two populations are markedly separated from
each other, we have determined that both the Sierra Nevada and the
coastal and southern California parts of the range both individually
meet the condition for discreteness under our DPS Policy.
Significance
Under our DPS Policy, once we have determined that a population
segment is discrete, we consider its biological and ecological
significance to the larger taxon to which it belongs. This
consideration may include, but is not limited to: (1) Evidence of the
persistence of the discrete population segment in an ecological setting
that is unusual or unique for the taxon, (2) evidence that loss of the
population segment would result in a significant gap in the range of
the taxon, (3) evidence that the population segment represents the only
surviving natural occurrence of a taxon that may be more abundant
elsewhere as an introduced population outside its historical range, or
(4) evidence that the discrete population segment differs markedly from
other populations of the species in its genetic characteristics.
For the California spotted owl, we first considered evidence that
loss of a population segment would result in a significant gap in the
range of the taxon. As discussed above, the southwestern and
northeastern parts of the range are separated by approximately 40 km
(25 mi). The loss of the coastal and southern California parts of the
range would result in the loss of the entire southwestern part of the
species' range and decrease species redundancy and ecological and
genetic representation, thus decreasing the species' ability to
withstand demographic and environmental stochasticity. The loss of the
Sierra Nevada range would result in the loss of 70 percent of the
species' range, also reducing the species' ability to withstand
demographic and environmental stochasticity. Therefore, the loss of
either part of the range would result in a significant gap in the range
of the California spotted owl.
We then considered evidence whether either of the discrete
population segments occur in an ecological setting that is unusual or
unique for the taxon. In the Sierra Nevada, a majority of California
spotted owls occur within mid-elevation mixed-conifer and mixed-
evergreen forest types, with few occurring in the lower elevation oak
woodlands of the western foothills (Guti[eacute]rrez et al. 2017, p.
109). As described above, in coastal and southern California,
California spotted owls are found in riparian/hardwood forests and
woodlands, live oak/big cone fir forests, and redwood/California laurel
forests, more so than the mixed-conifer communities (Guti[eacute]rrez
et al. 2017, p. xxvi). Use of these other communities is specific and
unique to owls in these areas. What is considered a large tree in
southern California may not be comparable to what is considered a large
tree in the Sierra Nevada. California spotted owls use a subset of
larger trees or snags as their nest trees, with the average nest tree
measuring 124 cm (49 in) dbh and 31 m (103 ft) tall in the Sierra
Nevada (Guti[eacute]rrez et al. 2017, p. 50). In southern California,
use of platform or old raptor nests is more common; thus, owls with
these types of nests were observed using trees as small as 33 cm (13
in) dbh (Tanner 2022, pers. comm.) with mean values of 75.0 cm (29.5
in) dbh (LaHaye et al. 1997, p. 45). Therefore, we conclude that, for
the two populations of California spotted owls, each persists in a
unique ecological setting for the species.
The evidence that a significant gap in the range of the taxon would
result from the loss of either discrete population segment meets the
significance criterion of the DPS Policy. Additionally, there is
evidence that the coastal and southern California and the Sierra Nevada
parts of the range have persisted in a unique ecological setting for
the species. Therefore, under the Service's DPS Policy, we find that
the Sierra Nevada and the coastal and southern California parts of the
California spotted owl's
[[Page 11608]]
range are significant to the taxon as a whole.
Distinct Population Segment Conclusion
Our DPS Policy directs us to evaluate the significance of a
discrete population in the context of its biological and ecological
significance to the remainder of the species to which it belongs. Based
on an analysis of the best available scientific and commercial data, we
conclude that both parts of the California spotted owl's range are
significant, because loss of either part would result in a significant
gap in the range of the taxon, and because the population segments
represent evidence that both parts of the range have persisted in a
unique ecological setting for the species. Therefore, we conclude that
both the Sierra Nevada and the coastal and southern California parts of
the California spotted owl's range are both discrete and significant
under our DPS Policy and are, therefore, uniquely listable entities
under the Act.
Based on our DPS Policy (61 FR 4722; February 7, 1996), if a
population segment of a vertebrate species is both discrete and
significant relative to the taxon as a whole (i.e., it is a distinct
population segment), its evaluation for endangered or threatened status
will be based on the Act's definition of those terms and a review of
the factors enumerated in section 4(a) of the Act. Having found that
both parts of the California spotted owl's range meet the definition of
a distinct population segment, we evaluate the status of both the
Sierra Nevada DPS and the Coastal-Southern California DPS of the
California spotted owl to determine whether either meets the definition
of an endangered or threatened species under the Act.
Regulatory and Analytical Framework
Regulatory Framework
Section 4 of the Act (16 U.S.C. 1533) and the implementing
regulations in title 50 of the Code of Federal Regulations set forth
the procedures for determining whether a species is an endangered
species or a threatened species, issuing protective regulations for
threatened species, and designating critical habitat for endangered and
threatened species. In 2019, jointly with the National Marine Fisheries
Service, the Service issued a final rule that revised the regulations
in 50 CFR part 424 regarding how we add, remove, and reclassify
endangered and threatened species and the criteria for designating
listed species' critical habitat (84 FR 45020; August 27, 2019). On the
same day, the Service also issued final regulations that, for species
listed as threatened species after September 26, 2019, eliminated the
Service's general protective regulations automatically applying to
threatened species the prohibitions that section 9 of the Act applies
to endangered species (84 FR 44753; August 27, 2019).
The Act defines an ``endangered species'' as a species that is in
danger of extinction throughout all or a significant portion of its
range, and a ``threatened species'' as a species that is likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The Act requires that we
determine whether any species is an endangered species or a threatened
species because of any of the following factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
These factors represent broad categories of natural or human-caused
actions or conditions that could have an effect on a species' continued
existence. In evaluating these actions and conditions, we look for
those that may have a negative effect on individuals of the species, as
well as other actions or conditions that may ameliorate any negative
effects or may have positive effects.
We use the term ``threat'' to refer in general to actions or
conditions that are known to or are reasonably likely to negatively
affect individuals of a species. The term ``threat'' includes actions
or conditions that have a direct impact on individuals (direct
impacts), as well as those that affect individuals through alteration
of their habitat or required resources (stressors). The term ``threat''
may encompass--either together or separately--the source of the action
or condition or the action or condition itself.
However, the mere identification of any threat(s) does not
necessarily mean that the species meets the statutory definition of an
``endangered species'' or a ``threatened species.'' In determining
whether a species meets either definition, we must evaluate all
identified threats by considering the species' expected response and
the effects of the threats--in light of those actions and conditions
that will ameliorate the threats--on an individual, population, and
species level. We evaluate each threat and its expected effects on the
species, then analyze the cumulative effect of all of the threats on
the species as a whole. We also consider the cumulative effect of the
threats in light of those actions and conditions that will have
positive effects on the species, such as any existing regulatory
mechanisms or conservation efforts. The Secretary determines whether
the species meets the definition of an ``endangered species'' or a
``threatened species'' only after conducting this cumulative analysis
and describing the expected effect on the species now and in the
foreseeable future.
The Act does not define the term ``foreseeable future,'' which
appears in the statutory definition of ``threatened species.'' Our
implementing regulations at 50 CFR 424.11(d) set forth a framework for
evaluating the foreseeable future on a case-by-case basis. The term
``foreseeable future'' extends only so far into the future as we can
reasonably determine that both the future threats and the species'
responses to those threats are likely. In other words, the foreseeable
future is the period of time in which we can make reliable predictions.
``Reliable'' does not mean ``certain''; it means sufficient to provide
a reasonable degree of confidence in the prediction. Thus, a prediction
is reliable if it is reasonable to depend on it when making decisions.
It is not always possible or necessary to define the foreseeable
future as a particular number of years. Analysis of the foreseeable
future uses the best scientific and commercial data available and
should consider the timeframes applicable to the relevant threats and
to the species' likely responses to those threats in view of its life-
history characteristics. Data that are typically relevant to assessing
the species' biological response include species-specific factors such
as lifespan, reproductive rates or productivity, certain behaviors, and
other demographic factors.
Analytical Framework
The SSA report documents the results of our comprehensive
biological review of the best scientific and commercial data regarding
the status of the species, including an assessment of the potential
threats to the species. The SSA report does not represent our decision
on whether the species should be proposed for listing as an endangered
or threatened species under the Act. However, it does provide the
scientific basis that informs our regulatory decisions, which involve
the further application of standards within the Act
[[Page 11609]]
and its implementing regulations and policies.
To assess California spotted owl viability, we used the three
conservation biology principles of resiliency, redundancy, and
representation (Shaffer and Stein 2000, pp. 306-310). Briefly,
resiliency is the ability of the species to withstand environmental and
demographic stochasticity (for example, wet or dry, warm or cold
years), redundancy is the ability of the species to withstand
catastrophic events (for example, droughts, large pollution events),
and representation is the ability of the species to adapt to both near-
term and long-term changes in its physical and biological environment
(for example, climate conditions, pathogens). In general, species
viability will increase with increases in resiliency, redundancy, and
representation (Smith et al. 2018, p. 306). Using these principles, we
identified the species' ecological requirements for survival and
reproduction at the individual, population, and species levels, and
described the beneficial and risk factors influencing the species'
viability.
The SSA process can be categorized into three sequential stages.
During the first stage, we evaluated the individual species' life-
history needs. The next stage involved an assessment of the historical
and current condition of the species' demographics and habitat
characteristics, including an explanation of how the species arrived at
its current condition. The final stage of the SSA involved making
predictions about the species' responses to positive and negative
environmental and anthropogenic influences. Throughout all of these
stages, we used the best available information to characterize
viability as the ability of a species to sustain populations in the
wild over time. We use this information to inform our regulatory
decision.
The following is a summary of the key results and conclusions from
the SSA report (Service 2022, entire); the full SSA report can be found
at Docket No. FWS-R8-ES-2022-0166 on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Summary of Biological Status and Threats
In this discussion, we review the biological condition of the
California spotted owl and its resources, and the threats that
influence the species' current and future condition, in order to assess
the species' overall viability and the risks to that viability.
We note that the California spotted owl SSA report discusses
California spotted owls at the individual, population, and species
level. The SSA does not make any analysis or conclusions with regard to
policy decisions, such as DPS findings, and does not include mention of
the two populations of the subspecies as DPSs. Instead, the SSA report
provides the biological information that our decisionmakers can then
use to inform those policy decisions. This proposed rule and its
supporting record contain the policy decisions and rationale.
Throughout this Summary of Biological Status and Threats discussion, we
discuss the coastal-southern California population of California
spotted owl, which we identify as the Coastal-Southern California DPS,
and the Sierra Nevada population of California spotted owl, which we
identify as the Sierra Nevada DPS.
California Spotted Owl Needs
Individual Needs
In this section, we assess the best available information to
identify the specific habitat components needed to support individual
fitness at all life stages for California spotted owls. Individual owls
must have adequate nesting, foraging, and roosting habitat to be
successful. For the purpose of the SSA report and this proposed rule,
the components of nesting, foraging, and roosting habitat that we
considered most significant include canopy cover, larger trees, and
habitat heterogeneity. Habitat heterogeneity is important to California
spotted owls as it provides protection from predators and extreme
weather conditions, variable microclimates, and habitat for different
prey species.
We acknowledge that these habitat components are not all-inclusive
and there may be other components of nesting, foraging, and roosting
habitat that are not being considered (such as prey). We also
acknowledge that a history of fire suppression in the western United
States, including throughout the range of both the Sierra Nevada DPS
and the Coastal-Southern California DPS, has caused many ecological
changes that are not fully understood (Mallek et al. 2013, p. 2).
However, we chose to focus on habitat components for which there are
available spatial data across the range of the species. Further, prey
is indirectly considered in our analysis since the primary California
spotted owl prey species also select for high canopy cover and coarse
woody debris (Waters and Zabel 1995, p. 858), which are considered here
as components of habitat heterogeneity. Populations of California
spotted owls require the same habitat components as individuals but at
larger scales.
Multi-layered, or complex, high canopy cover is considered an
important resource for spotted owls because it provides cool shaded
microclimates, camouflage and cover for protection from predators and
extreme weather conditions, and habitat for prey species (Forsman 1975,
pp. 4, 90, 105; Barrows 1981, p. 302; Forsman et al. 1984, p. 5). High
canopy cover from tall trees is associated with higher probability of
successful prey capture by California spotted owls (Zulla et al. 2022,
p. 8) and is an important predictor for California spotted owl nesting
habitat (North et al. 2017, pp. 166, 172-175). Multi-layered high
canopy cover around the nest tree and in territories is an important
factor associated with California spotted owl reproductive success
(Hunsaker et al. 2002, pp. 693-699; Blakesley et al. 2005, pp. 1554,
1558-1562). Areas with canopy cover greater than 70 percent are
considered optimal for California spotted owl nest sites and occupancy
sharply declines when canopy cover is less than 40 percent (Blakesley
et al. 2005, p. 1559; Seamans 2005, pp. iii, 90, 100; Seamans and
Guti[eacute]rrez 2007b, pp. 566, 568; Tempel et al. 2014a, pp. 2089,
2091, 2101; Tempel et al. 2016, pp. 747, 759). Even in southern
California where the habitat is naturally more fragmented with less
canopy cover available, California spotted owls still select for areas
with higher canopy cover relative to what is available (Smith et al.
2002, pp. 142-143). Further, California spotted owls in Yosemite
National Park had territory centers with average values of 40 percent
canopy cover in burned forests (Schofield et al. 2020, pp. 4-5).
The presence of large trees, defined as trees that are greater than
61 cm (24 in) dbh (Seamans and Guti[eacute]rrez 2007b, pp. 566, 571-
574; Tempel et al. 2014b, p. 2094; Jones et al. 2018, p. 344), is
important for California spotted owl foraging, roosting, and nesting.
California spotted owls tend to forage and roost in large trees, likely
due to the canopy cover provided by large trees and the important
resources such as shelter and food that large trees provide for prey
species (Laymon 1988, pp. 47, 71, 77, 100; Verner et al. 1992, pp. 9-
10, 60, 88; Moen and Guti[eacute]rrez 1997, pp. 1281, 1284). The
presence of tall (>48 m (157 ft)) trees, and the canopy cover they
provide, is the best predictor for California spotted owl occupancy,
and areas with a high density of large trees are considered high-
quality habitat (Blakesley et al. 2005, pp. 1554, 1558-1562; North et
al. 2017, pp. 166, 171-176). California spotted owls use a
[[Page 11610]]
subset of large trees or snags as their nest trees (LaHaye et al. 1997,
pp. 42, 47; Blakesley et al. 2005, pp. 1554, 1558-1562;
Guti[eacute]rrez et al. 2017, p. 50), and the nest tree itself is
critical for California spotted owl reproductive success because it
provides the space and structure needed for nests, along with
protection from predators and inclement weather. California spotted
owls do not build their own nests but rely on larger trees that provide
multi-layered high canopy cover with open cavities (created as a result
of fallen branches, woodpeckers, etc.), broken tops, platforms, and old
raptor nests (Guti[eacute]rrez et al. 2020, ``Habitat'' and
``Breeding'' sections). The nest tree chosen within a territory is
typically one of the oldest and largest live or dead trees within the
nesting territory with many defects like cracks, disease scars, or
decaying wood (Verner et al. 1992, pp. 6, 60, 71; North et al. 2000, p.
797).
The preferential use of mature forests with high canopy cover and
large trees is well-known for California spotted owls (Guti[eacute]rrez
et al. 2017, p. iii). However, there have been several recent studies
showing the importance of other habitat types, habitat edges, and
habitat heterogeneity (Atuo et al. 2019; Hobart et al. 2019; Kramer et
al. 2021b; Zulla et al. 2022; Wilkinson et al., in prep.). California
spotted owl occupancy, colonization, adult survival, and reproductive
success are all positively associated with the proportion of
structurally complex forests (Franklin et al. 2000, p. 539; Blakesley
et al. 2005, p. 1562; Tempel et al. 2014b, p. 2089; Tempel et al. 2016,
p. 747). The biological and physical components that create habitat
heterogeneity and complex structure are areas of multi-layered high
canopy cover, large trees, coarse woody debris, understory and mid-
story vegetation, patches of burned habitat, riparian habitat, large
diameter standing dead trees (snags), and some open areas within a
California spotted owl's home range.
Coarse woody debris (fallen dead trees and the remains of large
branches on the ground) is an important habitat feature for California
spotted owls because it provides food, shelter, and protection for
California spotted owl prey species, especially woodrats (Waters and
Zabel 1995, pp. 861-862; Pyare and Longland 2002, pp. 1016-1017; Innes
et al. 2007, pp. 1523, 1526; Kelt et al. 2013, p. 1208). Coarse woody
debris in areas of multi-layered high canopy cover is conducive for
fungal growth, a food source for many California spotted owl prey
species (Verner et al. 1992, pp. 71-72; Pyare and Longland 2002, pp.
1016-1017). Rates of prey capture by California spotted owls are
observed to be higher in taller multilayered forests, in areas with
higher vegetation heterogeneity, and near forest-chapparal edges
(Wilkinson et al. in prep., p. 2). There are a variety of habitats
within a heterogeneous landscape that California spotted owls use and
which may provide specific resources. The size of a California spotted
owl's home range increases as the heterogeneity, or number of different
vegetation patches, increase (Williams et al. 2011, p. 333); the
hypothesis is that there may be an optimal point of habitat
heterogeneity for California spotted owls beyond which territory
quality declines (Williams et al. 2011, p. 333).
Population Needs
Populations of California spotted owls must have adequate amounts
of nesting, foraging, and roosting habitat containing the habitat
components described above in sufficient amounts and the appropriate
configuration on the landscape to support a stable or increasing growth
rate. They also need connectivity between territories and home ranges.
Populations meeting these requirements are better able to withstand
stochastic events. In many instances, however, data are insufficient or
completely lacking regarding a population's size and growth rate. In
the absence of such data, we examine other characteristics that may
serve as surrogate indicators of general population health and,
subsequently, resiliency. Essentially, an assessment of the
availability of a species' identified needs (suitable habitat, food,
breeding sites) may allow us to make assumptions about the potential
resiliency of any given population. However, unless there is a
documented positive correlation between the availability of species'
needs and a population's known demographic condition, the uncertainty
regarding such assumptions must be made clear.
In the SSA report, we describe the demographic factors that are
considered important for California spotted owls, including natal
dispersal, survival, fecundity, occupancy, and population growth. We
describe the importance of each demographic factor to California
spotted owl persistence and how the individual needs influence these
factors.
There is little available information about dispersal and dispersal
habitat between the defined California spotted owl populations and
analysis units within the SSA report and this proposed rule. Dispersal
habitat is described for northern spotted owl as 50 percent of the
forest matrix outside of activity centers in stands with an average of
28 cm (11 in) dbh and 40 percent canopy closure (Thomas et al. 1990, p.
15). This contrasts with dispersal for Mexican spotted owls, which may
move across large areas of unforested habitat to access suitable
habitat on different mountain ranges (Guti[eacute]rrez et al. 1995, p.
5; Guti[eacute]rrez et al. 2017, p. 242). It is unknown how far
California spotted owls will disperse across unsuitable habitat to find
a new territory, but adult northern spotted owls have been found to
occasionally move long distances if forced out of a territory (Forsman
in litt. 2018, p. 22).
For dispersal to be successful, many of the individual needs must
be present within the areas to which California spotted owls disperse.
Canopy cover, large trees, and coarse woody debris all must be
available in sufficient amounts and the appropriate configuration on
the landscape (habitat heterogeneity) for juveniles or sub-adults to
successfully settle into a territory to begin breeding.
Survival for California spotted owls is closely linked to
population growth and is important for maintaining population
resiliency (Seamans and Guti[eacute]rrez 2007a, p. 57; Blakesley et al.
2010, p. 27). Adult California spotted owls have high annual survival
rates ranging from 0.796-0.814 in different study areas within analysis
units in southern California (LaHaye et al. 2004, p. 1056; Franklin et
al. 2004, p. 22), and 0.811-0.891 in study areas within analysis units
in the Sierra Nevada (Blakesley et al. 2001, p. 671; Franklin et al.
2004, p. 22; Blakesley et al. 2010, p. 10; Tempel et al. 2014a, p. 92).
In comparison, juvenile survival is difficult to estimate due to
dispersal, and has been found to be low, ranging from 0.087-0.333 in
study areas within analysis units in the Sierra Nevada (Blakesley et
al. 2001, p. 671; Tempel et al. 2014a, p. 92), and 0.368 for southern
California (LaHaye et al. 2004, p. 1056). For northern spotted owl,
juveniles tend to have high mortality during the dispersal phase
(Miller 1989, pp. 41-44; Forsman et al. 2002, p. 18).
All the individual needs discussed above influence survival. For
example, survival is related to the amount of forest dominated by
medium to large trees, high canopy cover, and habitat complexity
(Blakesley et al. 2005, p. 1554; Tempel et al. 2014b, pp. 2089, 2098;
McGinn et al. 2022, p. 9). In northern spotted owls, habitat
heterogeneity is correlated with higher survival rates (Franklin et al.
2000, p. 539).
Fecundity is defined as the ability to produce offspring and is
measured by the number of viable female offspring
[[Page 11611]]
that an individual can produce over a specific time period. Annual
reproductive output, measured by presence or absence of offspring in a
nest, for female California spotted owls in a demographic study in the
Sierra Nevada was found to range from 0.478-0.988 (Blakesley et al.
2010, p. 1). Reproduction throughout all the demographic studies has
ranged from no reproduction within a study area to nearly all birds
reproducing in a study area in a particular year (Franklin et al. 2004,
pp. 32-33; Seamans and Guti[eacute]rrez 2007a, p. 65; Blakesley et al.
2010, p. 17; MacKenzie et al. 2012, p. 597; Tempel et al. 2014a, p. 91;
Stoelting et al. 2015, p. 46). Fecundity, measured as female young
produced per female annually, has been found to range from 0.284-0.409
in the Sierra Nevada and to be 0.362 in southern California (Franklin
et al. 2004, pp. 11, 23).
Many of the individual needs discussed above influence fecundity.
Reproductive output decreases as non-forest habitat increases within
the area around the nest, and nest success increases as the presence of
large remnant trees within the nest stand increases (Blakesley et al.
2005, p. 1554). Reproduction is positively correlated to the foliage
volume above the nest tree (North et al. 2000, p. 797), although
habitat heterogeneity is also important for reproduction (Franklin et
al. 2000, p. 539; Tempel et al. 2014b, p. 2089; McGinn et al. 2022, p.
9) and foraging (Zulla et al. 2022, pp. 7-8). Annual variation in
weather also plays a role in reproductive success (North et al. 2000,
p. 797; Seamans and Guti[eacute]rrez 2007a, p. 57; MacKenzie et al.
2012, p. 597; Stoelting et al. 2015, p. 46). For example, California
spotted owls experienced increased fecundity when a dry breeding season
followed a previously wet year (LaHaye et al. 2004, pp. 1056, 1062).
Although survival of breeding California spotted owls is an important
factor that is closely connected to population growth, reproductive
output may be more influential to population growth because it varies
more than adult survival (Blakesley et al. 2001, p. 667; Seamans and
Guti[eacute]rrez 2007a, p. 57).
In the SSA report and this proposed rule, we define California
spotted owl occupancy as the stable (not transient) presence of at
least one adult within a territory. California spotted owls select and
defend territories in which they spend most of their life. California
spotted owl pairs will only reproduce once they have established an
occupied territory. The measure of occupancy has been found to be
strongly correlated with regional abundance of California spotted owls
and can provide reliable inferences on population trends (Tempel and
Guti[eacute]rrez 2013, pp. 1093-1093).
Many of the individual needs discussed above need to be present in
order for California spotted owls to occupy a territory. Occupancy is
generally higher and more consistent with an increasing proportion of
the territory containing large trees and high canopy cover (Blakesley
et al. 2005, p. 1554; Seamans and Guti[eacute]rrez 2007b, p. 572;
Roberts et al. 2011, p. 610; Tempel et al. 2014b, p. 2089;
Guti[eacute]rrez et al. 2017, p. vxii). As the proportion of forest
types that are not used for nesting (smaller, similar-aged young trees)
increases, occupancy tends to decrease (Blakesley et al. 2005, pp.
1554, 1560).
In the SSA report and this proposed rule, we define California
spotted owl population growth as the change in the number of
individuals within a particular study area, which correspond to our
analysis units. Population growth is determined by the demographic
factors of survival, fecundity, and occupancy, with fecundity likely
the most influential because it is more variable (Blakesley et al.
2001, p. 667; Seamans and Guti[eacute]rrez 2007a, p. 57; Seamans and
Guti[eacute]rrez 2007b, p. 566; Blakesley et al. 2010, p. 27; Tempel
and Guti[eacute]rrez 2013, pp. 1093-1094; Guti[eacute]rrez et al. 2017,
p. 99). Population growth is variable throughout study areas in the
Sierra Nevada DPS where we have available information, with documented
declines ranging from -50 percent to -31 percent in some study areas
and a population increase of 25 percent in another (Tempel et al.
2014a, pp. 86, 90-92; Conner et al. 2016, p. 15). The only available
demographic data for the Coastal-Southern California DPS is from the
San Bernardino National Forest. A population decline of -9 percent was
observed from 1987-1998, with more recent occupancy analyses showing
further declines in population size (LaHaye et al. 2004, pp. 1056,
1064; Tempel et al. 2022, p. 20, table 5). All individual needs
described above need to be present for positive California spotted owl
population growth.
Species Needs
At the species level, we assess the redundancy and representation
of the entire California spotted owl's range to better understand the
viability of the species. For the California spotted owl, we evaluate
redundancy by considering the number of resilient populations
distributed across the species' range. Having resilient populations
distributed across the range increases the species' ability to
withstand catastrophic events.
For this species, we evaluate representation by considering the
distribution of populations across their various ecological settings
and whether those populations are able to maintain adequate amounts of
genetic diversity. Having a variety of ecological settings that the
species can occupy and a breadth of genetic diversity increases the
species' ability to withstand and adapt to long-term environmental
changes.
Threats
Following are summary evaluations of eight threats analyzed in the
SSA report for the California spotted owl: wildfire (Factor A), tree
mortality (Factor A), drought (Factor A), climate change (Factor A),
fuels reduction and forest management (Factor A), competition and
hybridization with barred owls (Strix varia) (Factor E), rodenticides
(Factor E), and development (Factor A). We also evaluate existing
regulatory mechanisms (Factor D) and ongoing conservation measures.
In the SSA report, we also considered four additional threats:
Overutilization due to recreational, educational, and scientific use
(Factor B); disease (Factor C); predation (Factor C); and recreation
(Factor E). We concluded that, as indicated by the best available
scientific and commercial information, these threats are currently
having little to no impact on the California spotted owl and thus the
overall effect of these threats now and into the future is expected to
be minimal. Therefore, we will not present summary analyses of those
threats in this document, but we considered them in the current and
future condition assessments in the SSA report, and we will consider
them in our determination of the species' status. For full descriptions
of all threats and how they impact the species, please see the SSA
report (Service 2022, pp. 25-68).
For the purposes of this assessment, we consider the foreseeable
future to be the amount of time on which we can reasonably determine a
likely threat's anticipated trajectory and the anticipated response of
the species to those threats. For this proposed rule, we consider the
foreseeable future to be 40-50 years. This time period represents our
best professional judgment of future conditions related to climate
change for California, the California spotted owl's generation time,
and the regeneration time of medium to large trees.
Wildfire
Fire is a natural part of California spotted owl habitat (Verner et
al. 1992, pp. 247-248) and is necessary for maintaining heterogenous
forests and
[[Page 11612]]
overall habitat heterogeneity. Wildfire and associated tree mortality
can be beneficial or detrimental for the California spotted owl
depending on scale and severity. Fires with predominantly low to
moderate severity burn patterns, with small patches of high-severity
fire scattered throughout the fire perimeter, can increase habitat
heterogeneity, ultimately result in higher prey densities, increase
amounts of forest edge for California spotted owl foraging, and provide
for unburned refugia within the fire perimeter that have higher tree
survival and more vegetative cover during the immediate postfire years
(Roberts et al. 2011, p. 610; Lee et al. 2012, p. 792; Bond et al.
2013, pp. 114, 122; Eyes et al. 2017, p. 384; Blomdahl et al. 2019, pp.
1046, 1048, 1049). There is also evidence to suggest that more
pyrodiverse (spatial or temporal variability in fire effects; Jones and
Tingley 2021, p. 1) landscapes support greater habitat heterogeneity,
which may promote greater biodiversity (Steel et al. 2021, pp. 7-8;
Stephens et al. 2021, p. 5). For example, in areas where woodrats are
the primary prey species, a juxtaposition of mature forests and open
canopy patches promotes higher prey diversity and abundance, and
northern spotted owls preferentially select for these areas (Zabel et
al. 1995, p. 433; Ward and Noon 1998, p. 79; Franklin et al. 2000, p.
539; Zabel et al. 2003, p. 1027).
Although burned areas can reduce the amount of canopy cover
available, California spotted owls forage on the edge of and within
areas that have been burned at a range of severities (Bond et al. 2009,
p. 1116; Bond et al. 2016, p. 1290; Eyes et al. 2017, p. 375) although
typically avoiding larger areas of high-severity fire (Jones et al.
2016a, p. 304; Eyes et al. 2017, p. 383). Thus, many researchers
advocate for the use of ecologically beneficial fire to help sustain
California spotted owl habitat and report that low to moderate severity
fire minimizes the effects of future high-severity wildfire (Stephens
et al. 2019, pp. 395-396; Stephens et al. 2020, entire; Stephens et al.
2021, p. 5; Taylor et al. 2022, p. 4).
In contrast, large-scale, high-severity fires have a detrimental
effect on both the California spotted owl and its habitat. Large-scale
high-severity fire (often referred to as a megafire) is generally
defined as over 10,000 ha (24,711 ac) of area burned with 75-100
percent canopy mortality (Jones et al. 2016a, p. 300; Linley et al.
2022, pp. 6, 8). Megafires can degrade or destroy California spotted
owl habitat, completely incinerating large trees and canopy cover (Eyes
2014, p. ii; Roberts et al. 2015, pp. 112-115; Jones et al. 2016a, pp.
300-305). Habitat suitability for northern spotted owls decreased
postfire and depended on fire severity (higher fire severity resulted
in greater declines of habitat suitability) (Wan et al. 2020, p. 7);
thus, megafires have a greater potential to alter the availability of
suitable habitat.
The loss of habitat from large-scale, high-severity fires also
results in direct impacts to California spotted owl individuals and
populations. As megafires alter the number of large trees (including
nest trees), multi-layered high canopy cover, habitat heterogeneity,
and patch size, California spotted owl dispersal, fecundity, and
occupancy are subsequently reduced. It has been observed that large
patches of high-severity fire significantly reduce colonization
(dispersal), occupancy, and habitat use across the California spotted
owl's range (Eyes 2014, p. 42; Tempel et al. 2014b, p. 2089; Jones et
al. 2016a, pp. 300, 303-305; Eyes et al. 2017, pp. 381, 384; Jones et
al. 2019, p. 26; Jones et al. 2020, entire; Schofield et al. 2020, pp.
5-6; Jones et al. 2021a, p. 5; Tempel et al. 2022, p. 13) and for other
subspecies (Rockweit et al. 2017, entire; Lesmeister et al. 2019, p.
13; Duchac et al. 2021, p. 12). Fires may cause direct mortality to
eggs and juveniles during the nesting season, and fast-moving fires
also have the potential to cause direct mortality to adult California
spotted owl individuals (Jones et al. 2016a, p. 305). No data are
available on how many California spotted owls are killed annually by
direct impacts of large-scale, high-severity fire. Although most birds
are able to move to escape direct morality from fires, smoke from fires
can impact birds by damaging their lungs (Verstappen and Dorrestein
2005, p. 139). While many species have existed with frequent fire over
evolutionary time, megafires and extreme smoke events are novel
influences that may act as an additional selective pressure on certain
species (Nimmo et al. 2021, p. 5689). There is limited research on the
effects of wildfire smoke on wildlife in general, but there is clear
evidence that smoke can have both acute and chronic health impacts on a
variety of taxa, which may ultimately affect demographic rates
(Sanderfoot et al. 2021, p. 13).
As discussed above, high-severity fire has negative effects on
individual California spotted owls and their habitat, ranging from
reduced occupancy to direct mortality of individuals. However, several
publications conclude that spotted owls will continue to use areas
burned at high-severity and, therefore, there are no negative effects
of high-severity fire for California spotted owls (Lee and Bond 2015,
entire; Hanson et al. 2018, entire; Hanson et al. 2021, entire; Lee
2018, entire). We have reviewed these publications and acknowledge this
disagreement in the literature. However, our review of all the best
available science, including those sources that conclude no negative
effects, has led us to agree with the vast majority of science, which
concludes that overall spotted owls avoid large patches of high-
severity fire and that high-severity fire is increasing throughout
California and the western United States. For more analysis on the
conflicting results of these studies and our analysis, please see the
SSA report (Service 2022, pp. 27-28).
Current conditions in the California spotted owl's range may
contribute to ongoing fire risk, and depending on the portion of the
range and the land manager, fire management activities may vary.
Decades of fire suppression have led to overall higher canopy cover
from small and medium trees, higher dead biomass density, and more
surface fuels in forests of the western United States (Verner et al.
1992, pp. 247-248; Agee and Skinner 2005, p. 83). The historical fire
return interval for the Sierra Nevada was around 11-16 years, but fire
suppression over the last 100 years has led to a change in fire
behavior of larger, more severe fires in recent years (Safford and
Stevens 2017, pp. v-vi). The multi-layered high canopy cover and
biomass provide important habitat for California spotted owls but also
tend to increase the vulnerability of forests to high-severity fire
(Verner et al. 1992, pp. 251-258; Agee and Skinner 2005, p. 83) in
present day fire-suppressed forests. The higher fuel loads,
particularly large, dead wood (like snags and logs), tend to burn at
higher severity as densities increase (Lydersen et al. 2019, p. 7). In
a recent megafire, dead biomass directly contributed to the fire
effects observed, as areas with high amounts of dead biomass pre-fire
burned at high severity (Stephens et al. 2022, p. 8).
On top of the higher fuel loads, extended droughts and longer
wildfire seasons have led to larger and more severe fires in the
California spotted owl's range and throughout western North America
(Miller and Safford 2012, p. 41; Mallek et al. 2013, p. 1; Nigro and
Molinari 2019, p. 20; Parks and Abatzoglou 2020, p. 4; Safford et al.
2022, p. 12). In 2020 and 2021, more than 1 million ha (2.4 million ac)
burned in California, resulting in more area burned over these 2 years
than in the past 7 years of all California fires
[[Page 11613]]
combined (Safford et al. 2022, p. 5). An increase in high-severity fire
changes how fire interacts with important habitat features for
California spotted owls. For example, fire often killed, but left
standing, trees that would subsequently serve as locations for
California spotted owl nests. However, large patches of high-severity
fire burn hotter and can end up entirely consuming the features
important to California spotted owls. Between the years of 2000 and
2014, 7 percent of suitable California spotted owl nesting habitat (a
total of 85,046 ha (210,153 ac) out of 1,166,560 ha (2,882,633 ac)) was
burned either partially at moderate severity (typically 25-50 percent
tree basal area mortality) or entirely at high severity (typically >75
percent tree basal area mortality), causing >=50 percent tree basal
area mortality and reducing canopy cover to <25 percent (Stephens et
al. 2016, pp. 1, 9).
The size and severity of a fire determines how much it will impact
California spotted owls at the population level. If a high-severity
fire occurs in a large enough area, it can eliminate entire territories
or home ranges of California spotted owls, displacing individuals that
may or may not establish a new territory (Jones et al. 2016a, pp. 300-
305). Site occupancy by California spotted owls after wildfire appears
to be a function of the amount of suitable habitat remaining after the
fire (Guti[eacute]rrez et al. 2017, p. xxiii). If habitat becomes
unsuitable, it takes decades for large trees to reestablish on the
landscape. Based on fire activity and anticipated trends over the next
75 years, the cumulative amount of nesting habitat burned at >=50
percent tree basal area mortality will exceed the total existing
habitat in the Sierra Nevada (Stephens et al. 2016, pp. 1, 12). In
other words, the loss of suitable California spotted owl habitat would
exceed the rate of new forest growing post-fire (Stephens et al. 2016,
pp. 11-13). Thus, future habitat persistence for California spotted
owls is concerning given that high-severity fire appears to be
increasing across all lands (both public and private) occupied by
California spotted owls and throughout the western United States (Parks
and Abatzoglou 2020, pp. 4-5). When private lands are considered
separately, the odds of high severity fire occurring on industrially
managed forests and adjacent lands were 1.8 and 1.4 times higher,
raising some concern over California spotted owl persistence on private
lands (Levine et al. 2022, p. 4).
In the Sierra Nevada, the proportion of high severity fire
throughout the California spotted owl's range has dramatically
increased in recent years. The proportion of high-severity fire in
California montane forests in 2020 was on average 43-76 percent higher
than the combined average between 1984 and 2008, and was three to six
times higher than the estimates of pre-Euroamerican settlement (Safford
et al. 2022, p. 17). Between 1984-2019, 1,084,171 ha (2,679,044 ac;
55.7 percent) burned throughout the California spotted owl range in the
Sierra Nevada with 317,605 ha (784,820 ac; 46.6 percent) burned at high
severity (Keane in litt. 2022, p. 3). In contrast, between 2020 and
2021, 862,625 ha (2,131,593 ac; 44.3 percent) burned throughout the
California spotted owl's range with almost 363,812 ha (899,000 ac; 53.4
percent) of that at high severity (Keane in litt. 2022, p. 3). This
comparison illustrates how megafires in 2020 and 2021 burned more
habitat at high severity in 2 years than fires over the past three and
a half decades. In addition, between 1984 and 2021, 50 percent of
California spotted owl PAC acres have been impacted by wildfire, with
56 percent of that total burned in 2020 and 2021. Further, of the 56
percent that burned between 2020 and 2021, 65 percent burned at high
severity (Keane in litt. 2022, p. 5). Because California spotted owls
are displaced from areas where the entire PAC or majority of the PAC
has burned at high severity, it is unlikely the species will continue
to persist in these areas until the habitat can recover, which can take
decades.
We conducted a fire severity analysis within the entire California
spotted owl's range; details of the methodology used in this analysis
are available in the SSA report (Service 2022, pp. 29-30). Of the
California spotted owl's range, approximately 47 percent burned between
1984 and 2021, with 15 percent at high severity. Most of the area
burned at high severity occurred in 2020 and 2021, with 2 percent and 4
percent, respectively (Service 2022, table 3). Additionally, based on
an existing dataset from the California Department of Forestry and Fire
Protection of the potential threat of future wildfire in California,
the majority of the California spotted owl's range occurs within the
very high wildfire threat category (Service 2022, figure 8). Much of
the coastal-southern California population of the California spotted
owl falls within the extreme fire risk. This dataset contains fire
information through 2014, and so does not consider how the recent fires
from 2014 to 2021 affect future fire threat. Overall, we expect that
the pattern of both area burned and wildfire severity will continue or
increase into the future due to the effects of climate change.
Some regulatory mechanisms and conservation measures can reduce the
potential severity or scale of wildfires. Wildfire fuel reduction
treatments, such as prescribed fire and mechanical thinning, can reduce
the amount or degree of spotted owl habitat loss from a high-severity
fire, and a balanced approach to fuel reduction treatments may ensure
suitable California spotted owl habitat is maintained (Jones et al.
2016a, p. 305; Service 2017, pp. 24-25; Chiono et al. 2017, p. 1; Jones
et al. 2021a, entire). The 2004 USFS Sierra Nevada Forest Plan
Amendment has a goal of actively restoring fire-adapted ecosystems by
reducing unnaturally dense conditions, and there are also measures in
place in the framework to avoid disturbance within California spotted
owl PACs to the greatest extent possible (USFS 2004, pp. 34-35). Fuel
reduction treatments are actively taking place on USFS land, but
special considerations, including the timing of treatments to avoid the
breeding season and the methods that are used, are evaluated to avoid
impacts to owls within PACs. In 2017 and in 2020, an MOU was signed by
Sierra Pacific Industries, California Department of Forestry and Fire
Protection, National Fish and Wildlife Foundation, and the USFS to
coordinate on certain actions that may contribute to forest fuel
reductions and California spotted owl conservation. The purpose of the
MOU is to try to minimize the threat of large-scale, high-severity fire
while still providing quality habitat for California spotted owls.
However, large-scale, high-severity fire cannot be completely addressed
by regulatory mechanisms. Fuel reduction treatments may not prevent
catastrophic damage in an extreme fire event; however, when fire is a
part of the fuel reduction treatment, future fire severity can be
reduced and more fire treatments should be included to achieve fuels
reduction goals, including areas surrounding spotted owl nests and
riparian corridors (North et al. 2021, pp. 527, 529; Taylor et al.
2022, p. 4).
High-severity fire is likely to continue to be a threat into the
future for California spotted owls. Although some individuals could be
harmed or killed by large fires, the primary impact of this threat is
habitat-based. These habitat changes also affect demographic
parameters: following high severity fires, colonization declines and
territory extinction increases, leading to overall declines in
occupancy (Tempel et al. 2022, pp. 13-16). Overall, large-scale, high-
severity fire is currently and will
[[Page 11614]]
likely continue to be a threat throughout the range of the California
spotted owl, including for both the Sierra Nevada and the coastal-
southern California populations.
Tree Mortality
Widespread increases in tree mortality have been occurring in
California due to drought, disease, and bark beetles above historical
levels of mortality (van Mantgem et al. 2009, pp. 521-523; Asner et al.
2015, p. 249; McIntyre et al. 2015, p. 1458; Preisler et al. 2017, p.
166). When tree stand densities are too high compared to available
resources (water, light, nutrients), trees become stressed due to
competition for resources and thus are more vulnerable to mortality
(USFS 2017, p. 9). Large trees are often especially prone to drought,
disease, and beetle-related mortality (Smith et al. 2005, p. 266;
Mueller et al. 2005, p. 1085; Allen et al. 2010, p. 668; McIntyre et
al. 2015, p. 1458). Increased tree mortality may be contributing to
loss of California spotted owl habitat (Guti[eacute]rrez et al. 2017,
p. 137), but the magnitude of the impacts on California spotted owls is
uncertain. Large-scale tree mortality reduces the availability of
canopy cover and large trees, potentially resulting in California
spotted owl population declines because of reduced habitat available
for dispersal and occupancy. However, some tree mortality events can
have some positive effects on California spotted owl habitat, as these
events contribute to habitat heterogeneity and the availability of
coarse woody debris for prey species.
Between 2010 and 2016, an estimated 102 million trees died across
about 3,106,367 ha (7,676,000 ac) throughout California (Tree Mortality
Task Force 2017, p. 2). By February 2019, total tree mortality in
California increased to an estimated 147 million dead trees (Cal Fire
and USFS 2019, p. 1). The latest estimate shows that between 2010 and
2021, the drought combined with subsequent beetle attacks resulted in
approximately 173 million dead trees in California with approximately
3.3 percent of the surveyed forest area in 2021 showing signs of
elevated mortality (USFS 2021, p. 5). The tree mortality events are
particularly severe in the southern Sierra Nevada area. Most of the
tree mortality observed is due to effects from the 2012-2016 drought,
with less mortality occurring from 2018-2021; however, another drought
period started in 2020 (USFS 2021, p. 5).
In 2015, the Governor of California declared a state of emergency
due to the unprecedented number of dead and dying trees in the State.
In response, the California Tree Mortality Task Force, which is now the
Forest Mortality Working Group within the California Wildfire and
Forest Resilience Task Force, was created to coordinate emergency
protective actions and monitor ongoing conditions. The group collects
and manages the tree mortality data, provides recommendations to land
managers, presents grants for research funding, and provides public
outreach. The task force will likely continue to provide the services
listed into the future due to the ongoing and large-scale nature of the
tree mortality events in California.
Regulatory mechanisms and management actions could provide some
protection from the effects of tree mortality. Efforts to restore
historical forest conditions and reduce stand densities through fuels
reduction treatments (mechanical thinning, prescribed fire, etc.) may
indirectly contribute to reducing future tree mortality by reducing
competition. Further, the goal should be to eliminate the excessive
levels of tree mortality currently being observed in the landscape and
not limit all tree mortality, as tree mortality is a natural part of
the forest ecosystem and ultimately creates features important to
California spotted owls (snags, tree cavities). Tree mortality is
likely to continue throughout the range of the California spotted owl
due to predicted increases in drought conditions that will likely
continue to weaken trees and make them susceptible to bark beetles and
disease (Millar and Stephenson 2015, pp. 823-826; Young et al. 2017,
pp. 78, 85). Excessive tree mortality is likely to continue to be a
threat into the future for the California spotted owl.
Drought
California has experienced extreme drought conditions in 2007-2009
and 2012-2016 (Williams et al. 2015, pp. 6823-6824; CDWR 2021, p. 4),
and as of May 2022, a majority of the California spotted owl's range is
considered in severe to moderate drought (CDWR 2022, entire).
Anthropogenic warming likely contributed to more recent drought
anomalies and increases the overall likelihood of extreme droughts in
California into the future (Williams et al. 2015, pp. 6819, 6826; CDWR
2022, entire).
Drought conditions can negatively impact the California spotted
owl's ecological needs. As described above, drought conditions
contribute to tree mortality, which reduces canopy cover, likely
leading to a decline in occupancy. Further, drought conditions likely
reduce the availability of prey species (Franklin et al. 2000, p. 589;
Glenn et al. 2010, p. 2549; Glenn et al. 2011, p. 174). Drought and hot
temperatures in the previous summer are linked to lower reproductive
success in California spotted owls (LaHaye et al. 2004, p. 1066) and
lower survival and recruitment in northern spotted owls in the next
breeding season (Glenn et al. 2011, pp. 159, 174). Inversely, increases
in precipitation either before or after the nesting season are linked
to increased survival and fecundity in all three subspecies of spotted
owls (Seamans et al. 2002, p. 321; LaHaye et al. 2004, pp. 1056, 1064;
Glenn et al. 2011, pp. 159, 174). Thus, drought likely negatively
impacts the California spotted owl's habitat components, and its
demographic needs of dispersal, survival, fecundity, and occupancy. No
regulatory mechanisms or conservation measures in place ameliorate the
direct impacts of drought. It is likely that drought conditions will
continue to be a threat into the future across the California spotted
owl's range and will likely worsen due to the effects of climate
change.
Climate Change
Scientific measurements spanning several decades demonstrate that
changes in climate are occurring and that the rate of change has been
faster since the 1950s. There is strong scientific support for
projections that warming will continue through the 21st century, and
that the magnitude and rate of change will be influenced substantially
by the extent of greenhouse gas emissions (Meehl et al. 2007, pp. 760-
764, 797-811; Ganguly et al. 2009, pp. 15555-15558; Prinn et al. 2011,
pp. 527, 529; IPCC 2013, pp. 19-23).
Projected changes in climate and related impacts can vary
substantially across and within different regions of the world (IPCC
2013, pp. 15-16). Therefore, we used downscaled projections from
California's Fourth Climate Change Assessment, including the following
four regional assessments that cover the California spotted owl's
range: Sierra Nevada (Dettinger et al. 2018, entire), the Central Coast
Region (Langridge 2018, entire), Los Angeles (Hall et al. 2018,
entire), and San Diego (Kalansky et al. 2018, entire). Ten global
climate models were used for all four regional assessments, and each
model considered two different emissions scenarios, one in which
greenhouse gas emissions continue to increase into the next century
(RCP 8.5) and one in which greenhouse gas emissions stabilize by mid-
century and then decline to levels
[[Page 11615]]
seen in the 1990s by the end of the century (RCP 4.5) (Dettinger et al.
2018, pp. 15, 17; Hall et al. 2018, p. 9; Kalansky et al. 2018, p. 18;
Langridge 2018, p. 12).
Under both emissions scenarios, projected annual average
temperatures throughout the California spotted owl's range are
projected to increase. The largest increases under both emissions
scenarios and timeframes are projected for the eastern portions of the
Sierra Nevada (Dettinger et al. 2018, p. 17, figure 2.3). Projected
changes will result in greater temperatures than historically
experienced in the Sierra Nevada, and this degree of temperature change
will likely result in a shift in the rain to snow transition by 1,500-
3,000 feet (Dettinger et al. 2018, pp. 17, 20). Projected temperature
increases are more pronounced in the inland portions of the Central
Coast Region, with the ocean acting as a buffer for coastal areas
(Langridge 2018, p. 14, figure 4). In addition, the average number of
extremely hot days (defined as days that exceed the 98th percentile of
observed, historical (1961-1990) daily maximum temperatures between
April 1 and October 31) are expected to increase throughout the Central
Coast Region (Langridge 2018, pp. 14-15, table 4).
Regional assessments covering southern California include the Los
Angeles and San Diego Regional Assessments (Hall et al. 2018, entire;
Kalansky et al. 2018, entire). Projected annual average maximum
temperatures throughout the Los Angeles Region increase under both
emissions scenarios (Hall et al. 2018, p. 10, figure 2). For the San
Diego Region, projected annual average maximum and minimum temperatures
also increase under both emissions scenarios. Similar to the Central
Coast Region, these changes will be more pronounced in the interior
portions of the Los Angeles and San Diego Regions (Hall et al. 2018, p.
11, figure 3).
In addition to temperature projections, the regional assessments
for California's Fourth Climate Change Assessment also considered
future changes in precipitation, both the amount and the timing. Within
the Sierra Nevada Region, changes in precipitation are projected to be
relatively small and will vary depending on the area. In general,
average annual precipitation in the southern portion of the Sierra
Nevada Region is projected to stay similar or decrease by 5 percent,
regardless of emission scenario. In other portions of the Sierra Nevada
Region, particularly along the eastern side, the amount of
precipitation is projected to increase by up to 10 percent. In addition
to projections showing the northern portions of the range will receive
more precipitation than southern portions, areas at higher elevations
are also more likely to receive an increase in precipitation. Although
the average change in precipitation is projected to be small, the
models show there will be an increase in extreme conditions with more
dry days overall interspersed with higher intensity precipitation
events, when they do occur (Dettinger et al. 2018, p. 19). Further, in
some areas more precipitation will fall as rain instead of snow, as the
rain to snow transition is projected to shift by 457-914 m (1,500-3,000
ft) (Dettinger et al. 2018, pp. 17, 20).
Similar to the Sierra Nevada Region, interannual variability within
the Central Coast Region is expected to increase with more dry days
overall, but more precipitation when rain events do occur (Langridge
2018, p. 16). In southern California, the amount of precipitation in
the Los Angeles and San Diego Regions is highly variable (Hall et al.
2018, p. 12, figure 5; Kalansky et al. 2018, p. 24). Similar to other
regions, projections for the Los Angeles and San Diego Regions show an
increase in extreme conditions such as high-intensity precipitation
events, known as atmospheric rivers, and severe drought conditions
(Hall et al. 2018, pp. 13-14, figure 6; Kalansky et al. 2018, pp. 24-
25, figures 7 and 9).
Because the California spotted owl has a wide geographic range and
the projected changes in climate vary across the range, the effects
those changes will have on the species and its habitat will vary.
Future climate projections of Sierra Nevada vegetation distribution
indicate that low- and mid-elevation forests are vulnerable to
conversion to unsuitable habitat for California spotted owls, such as
shrublands and grasslands (Guti[eacute]rrez et al. 2017, p. 215). These
changes in climate may also include potential shifts in forest
communities upslope, which would have impacts on both the California
spotted owl's habitat and prey habitat (Guti[eacute]rrez et al. 2017,
pp. 132, 215, 288). This potential upslope shift in suitable habitat
may mitigate some climate-induced habitat threats over ecological time,
although it would require many decades for suitable large nest trees to
develop in areas where they do not currently exist (Guti[eacute]rrez et
al. 2017, p. 215). These differences in net habitat loss versus net
habitat gained under future climate scenarios will likely depend not
only on the rate of warming but also how individual plant and prey
species respond (Seamans and Guti[eacute]rrez 2007a, p. 61).
Changing climatic conditions may have direct impacts on California
spotted owl physiology, survival, reproduction, recruitment, or
population growth. The thermal neutral zone (the range of temperatures
tolerated by a warm-blooded animal) for California spotted owls is
18.2-35.2 [deg]C (64.8-95.4 [deg]F) (Weathers et al. 2001, p. 682).
Above this zone, California spotted owls experience heat stress
(Weathers et al. 2001, p. 678). The relatively low thermal neutral zone
may make California spotted owls more susceptible to increased
temperatures or cause behavioral or habitat shifts to cooler
microclimates on the landscape. Behaviorally, California spotted owls
can select cooler microclimates for roosting, especially within warmer
forest stands (McGinn et al. in review, p. 2). Changing climatic
conditions may also have indirect impacts including changes in habitat
and prey distribution, abundance, and quality. California spotted owls
must be able to adjust to the changing climate through behavioral
changes, spatial shifts, or adaptation in order to persist. Under
projected warming conditions in the future, cooler microclimate refugia
are likely to be critically important for the persistence of California
spotted owl individuals and populations (McGinn et al. in review, p.
3). It is likely that climate change will reduce the quantity and
quality of California spotted owl habitat, which would likely result in
population impacts, including a decrease in dispersal, fecundity, and
occupancy. Both the habitat components and demographic factors of
California spotted owls will likely be impacted by climate change, but
the full extent of impacts climate change may have on California
spotted owls is poorly understood (Wan et al. 2018, p. 690).
Climate modeling specific to the central Sierra Nevada portion of
the California spotted owl's range has shown that maintaining high
canopy cover, especially at higher elevations, will be important for
California spotted owls to persist into the future, as high canopy
cover helps maintain future refugia for individuals to select for
cooler microclimates (Jones et al. 2016b, entire). Under both a low
climate change prediction scenario (RCP 2.6) and a high climate change
scenario (RCP 8.5), California spotted owl occupancy decreases in
comparison to baseline climate conditions (Jones et al. 2016b, p. 901).
However, this model did not consider projected increases in frequency
and size of high-severity fires due to climate change, which would
likely result in more significant declines
[[Page 11616]]
in occupancy than predicted by the model (Jones et al. 2016b, p. 903).
Earlier modeling of spotted owl response to projected climate changes
show that different subspecies and populations of spotted owls are
anticipated to respond differently across their ranges (Peery et al.
2011, p. 14).
The climate change projections described above suggest increasing
interannual climate variability throughout the range of the California
spotted owl. Interannual climate variability is defined as when annual
weather patterns differ from historical average climate, including
prolonged drought conditions, heavy rain conditions, and higher or
lower than average temperatures. Interannual climate variability has
been shown to have impacts on the survival and reproductive success of
California spotted owls. Drought conditions and hot temperatures during
the summer have been found to reduce fecundity in California spotted
owls during the next breeding season (LaHaye et al. 2004, p. 1056).
Increases in precipitation either before or after the nesting season
are linked to increased survival and fecundity, whereas increased
precipitation during the nesting season reduces reproductive success
(North et al. 2000, p. 804; LaHaye et al. 2004, pp. 1056, 1064). It is
hypothesized that northern spotted owls exhibit a bet-hedging
reproduction strategy and that an absence of reproduction is linked to
environmental conditions (Franklin et al. 2000, pp. 539, 576).
California spotted owls likely have a similar bet-hedging reproductive
strategy (Stoelting et al. 2015, p. 46; Guti[eacute]rrez et al. 2017,
pp. 14-15). California spotted owls are sensitive to warm temperatures
and, therefore, may be physiologically sensitive to weather patterns
with increased temperatures (Weathers et al. 2001, p. 684).
Temperature, either too hot or too cold, may affect spotted owls
directly by increasing energy demands (Guti[eacute]rrez et al. 2017, p.
20). This increase may have direct impacts on the physiology of spotted
owls or on breeding if mates must bring more food to the nest for the
female to survive. Increased interannual climate variability due to
climate change will likely impact the California spotted owl throughout
its range, which would result in lower fecundity.
Regulatory mechanisms and management actions that are or could
potentially provide some protection from the effects of climate change
include the Clean Air Act (42 U.S.C. 7401 et seq.) and the California
Global Warming Solutions Act. Both address climate change by reducing
greenhouse gas emissions within the United States and California,
respectively. There are no regulatory mechanisms or management actions
that fully address the effects of the climate change.
The effects of climate change will continue to impact California
spotted owls into the future by exacerbating the negative influencing
factors described above, especially extreme weather events such as
prolonged drought and severe storms. The loss or reduction of suitable
habitat throughout the California spotted owl's range will likely
reduce the subspecies' reproduction, occupancy, survival, recruitment,
and population growth.
Fuels Reduction and Forest Management
Forest management has long been a controversial topic regarding
species that require old growth forest habitat, including the spotted
owl (Guti[eacute]rrez 2020, p. 337). With the increasing frequency and
extent of high-severity fire in California in recent decades, fire
mitigation has become a key issue for spotted owl management and
conservation. The goal of fuels management is to reduce the buildup of
fuels in forests that contribute to these large-scale, high-severity
fires, which can effectively mitigate subsequent fire behavior and
their effects, even under extreme weather (Hessburg et al. 2021, p. 7;
Prichard et al. 2021, p. 9). The long-term benefits of properly managed
fuel treatments for reducing the risk of severe wildfire are likely to
outweigh the short-term negative impacts to spotted owl habitat (Ager
et al. 2007, pp. 54-55; Roloff et al. 2012, p. 7; Jones et al. 2021b,
pp. 4-5). These trade-offs are complex and ultimately depend on the
extent that treatments have negative impacts to owl habitat and the
magnitude of effects from subsequent wildfires (Jones et al. 2021b, p.
2). Fuels reductions and forest management practices vary throughout
the California spotted owl's range. Below, we discuss clearcutting,
mechanical thinning, salvage logging, and prescribed fire, and the
positive and negative influences that these practices can have on the
species.
Clearcutting, sometimes referred to as even-aged management, is
defined as an even-age regeneration or harvest method that removes all
trees in the stand, producing a fully exposed microclimate for the
development of a new age class in one entry (Guti[eacute]rrez et al.
2017, p. 292). The natural range of variation for forest gaps in the
Sierra Nevada has been found to range from 0.03-1.17 ha (0.07-2.89 ac)
(Safford and Stevens 2017, p. 140), and within the SSA report and this
proposed rule, clearcutting refers to complete removal greater than the
natural range of variation.
Clearcutting is a mostly historical threat to California spotted
owls, although it still occurs in some areas of the Sierra Nevada. By
removing entire stands of trees, clearcutting reduces the amount of
large trees, high canopy cover, and coarse woody debris available for
California spotted owls. Commercial timber harvest no longer occurs
within the California spotted owl's range on public lands in the
Coastal-Southern California DPS (Guti[eacute]rrez et al. 2017, p. 254).
Clearcutting also does not occur on USFS lands on the eastern side of
the Sierra Nevada range (Boatner in litt. 2022). Clearcutting still
occurs on private timber harvest lands but is limited to 8.1-ha (20-ac)
parcels by California State forest practice rules (California Code of
Regulations (CCR), title 14, article 3 (14 CCR 913 et seq.)).
Additionally, there must be at least 91.44 m (300 ft) of forested area
between clearcuts, and adjacent lands cannot be cut for at least 5
years (14 CCR 913 et seq.). Even with the reduction of clearcutting in
recent history, it will take decades or centuries for large trees to
grow back from the past removal practices; therefore, there are
residual effects that may be impacting California spotted owl
populations and the habitat that is available (Jones et al. 2018, p.
1). California spotted owls may use clearcut habitat, likely for
foraging activities, but these areas are used significantly less than
high canopy cover and large tree areas (Atuo et al. 2019, pp. 295, 301-
302).
Mechanical thinning is a forest management strategy to thin trees
either in even or uneven-aged stands by removing trees in rows, strips,
or by using fixed pacing intervals, usually implemented to meet forest
management objectives. It can be done for commercial harvest of trees
or to reduce fuel loads to decrease the likelihood of large-scale,
high-severity fires (Guti[eacute]rrez et al. 2017, p. 292). Within the
SSA report and this proposed rule, we use ``mechanical thinning'' to
include both individual tree selection (new age classes are created in
uneven-aged stands by removing individual trees of all size classes
more or less uniformly throughout the stand to achieve desired stand
structure) and group tree selection (treatment involves salvage harvest
in a stand where small groups of trees are harvested because of tree
mortality due to windstorm, wildfire, insects, disease, or other
animals).
Mechanical thinning is actively used to manage forests occupied by
California
[[Page 11617]]
spotted owls and can have positive or negative impacts on the
California spotted owl's habitat and demographics depending on the
specific methods used. The 2004 Sierra Nevada Forest Plan Amendment
promotes reducing, using methods including mechanical thinning,
unnaturally dense forest conditions on the landscape to reduce the risk
of large-scale, high-severity fire (USFS 2004, pp. 34-35). Minimal area
is treated mechanically, especially when compared to area burned by
wildfire (566,560 ha (1,400,000 ac) burned between 2017-2020 versus
61,852 ha (152,842 ac) previously treated; North et al. 2021, p. 524).
Treatments are located to avoid California spotted owl activity centers
to the greatest extent possible (USFS 2004, pp. 34-35), which often
leaves the PACs untreated and potentially vulnerable to stand-replacing
fires (Stephens et al. 2019, p. 395). Further, strategic thinning can
promote forest resiliency, but removing some large, fire-intolerant
tree species like fir and cedar may be necessary to promote future
resilience of forested habitat (Stephens et al. 2020, entire; North et
al. 2021, p. 530).
Resilience of California spotted owl habitat results from low stand
densities, which reduces competition and allows trees to grow, so more
intensive fuels treatments (mechanical thinning and prescribed fire)
may be needed to achieve historically lower levels of tree densities
(North et al. 2022, p. 6). When conducted outside California spotted
owl activity centers, mechanical thinning will likely reduce the amount
of damage the habitat may experience due to high-severity fire while
also minimizing short-term habitat impacts (Stephens et al. 2014, p.
904; Tempel et al. 2015, p. 1; Chiono et al. 2017, p. 1). Strategic
mechanical thinning to reduce fuel loads and reduce the risk of large-
scale, high-severity fire, while also maintaining the necessary forest
structure components of large trees, multi-layered high canopy cover,
habitat heterogeneity, and coarse woody debris, will be important for
California spotted owl management into the future (Jones et al. 2016a,
p. 305; Tempel et al. 2016, p. 305; Jones et al. 2019, p. 22).
Strategically placed landscape fuel treatments can decrease future fire
severity while also increasing seedling densities (Tubbesing et al.
2019, p. 54). Many studies emphasize the importance of scaling-up fuel
reduction treatments (mechanical thinning and prescribed fire) and
suggest an increased benefit of treating within California spotted owl
territories for long-term persistence, although positive effects would
not be observed until mid-century and treatments should still strive to
maintain large trees and high canopy cover forest (Jones et al. 2021b,
p. 3; Safford et al. 2022, p. 17).
This fuels management technique has little to no impact on
occupancy if carried out in a strategic way (for example, maintaining
some patches of high canopy cover mixed with patches of moderate canopy
cover to provide for the primary habitat of California spotted owls and
incorporating limited operating periods that restrict activities from
occurring during the critical nesting period) (Tempel et al. 2016, p.
747). However, mechanical thinning can decrease California spotted owl
occupancy and is negatively correlated with reproduction (Tempel et al.
2014a, p. 2089; Stephens et al. 2014, p. 903; Tempel et al. 2022, p.
19). Although one study detected some negative effects of fuels
reduction treatments on California spotted owls in southern California,
the authors suggested that occupancy declines were small compared to
the potential negative effects of fire (Tempel et al. 2022, p. 22).
Similarly, there is evidence of reduced foraging in fuel treatment
areas that have a moderate to high proportion of forest gaps with
little to no canopy cover (Gallagher et al. 2018, pp. 487, 494-499).
Forest thinning has complex effects on both California spotted owls and
their mammalian prey species. Thinning may have negative short-term
effects on prey species by increasing the risk of predation by removing
above-ground cover and reducing canopy connectivity, and thinning may
remove suitable nesting substrates; however, there may be positive
effects in the long term (over decades) by promoting growth of the
midstory layer of trees that is favorable to certain mammalian prey
species (Wilson and Forsman 2013, p. 79).
Salvage logging is a practice where damaged or dying trees are
removed to recover their economic value and promote forest health
(Guti[eacute]rrez et al. 2017, p. 293; Jones et al. 2020, p. 11).
Salvage logging often occurs after natural disturbances such as
wildfires, disease, and insect infestation (Lindenmayer et al. 2008, p.
4). Post-fire fuels treatment that includes the removal of smaller
trees and surface and ladder fuels is not generally considered a threat
to California spotted owls relative to the threat posed by megafires
(Jones et al. 2021b, p. 7). Negative effects of salvage logging have
been documented for wildlife, vegetation, and soils, but there is a
paucity of literature on the subject, which may lead to inaccurate
comparisons when studies occur across varied geographic regions;
nevertheless, the negative effects may be mediated by altering
equipment, timing of operations, and harvest prescriptions to leave
more large snags (Nemens et al. 2019, entire). California spotted owls
inhabit areas of low-medium severity fire, patchy high-severity fire,
and areas with dead trees; therefore, salvage logging likely reduces
the amount of habitat available for California spotted owls
(Guti[eacute]rrez et al. 2017, p. 276). Salvage logging can result in
short-term decreased vegetation regrowth (Wagenbrenner et al. 2015, p.
176), which would likely impact prey species for California spotted
owls. However, salvage logging does not appear to make much difference
in long-term vegetation regrowth, so salvage logged areas have the
potential to again become suitable habitat after the centuries it takes
to establish large trees in the area (Peterson and Dodson 2016, p. 56).
Salvage logging in certain instances may also be necessary to reduce
future fire severity as high levels of dead biomass are associated with
high-severity fire (Lydersen et al. 2019, p. 7; Stephens et al. 2022,
p. 8); salvage logging may also be required for restoration personnel
to safely access an impacted site for re-planting activities (Sawyer in
litt. 2022).
The California spotted owl's response to salvage logging appears to
be at least partly dependent on the characteristics of the fire after
which it occurs, which can make it difficult to analyze these
relationships (detailed in Jones et al. 2019). For example, salvage
logging that occurs within a large, burned area is less likely to
negatively impact spotted owls relative to salvage logging that occurs
within a smaller burned area (Jones et al. 2020, p. 12). There is some
evidence that northern spotted owl (Clark et al. 2012, p. 15) and
California spotted owl occupancy decreases with salvage logging (Lee et
al. 2013, p. 1327; Lee and Bond 2015, p. 228; Hanson and Chi 2021, p.
5), while other evidence suggests that salvage logging has no effect on
California spotted owl persistence or colonization (Jones et al. 2021b,
p. 5). Salvage logging can be a threat to California spotted owls when
their habitat components of large trees, coarse woody debris, and
habitat heterogeneity are removed from the landscape, resulting in a
decrease in occupancy at the population level. The 2004 Sierra Nevada
Forest Plan Amendment prohibits salvage harvest in California spotted
owl PACs unless a biological evaluation determines that the areas
proposed for harvest have been rendered unsuitable for the purpose they
were intended (i.e., California
[[Page 11618]]
spotted owl habitat) by a catastrophic stand-replacing event (USFS
2004, pp. 52-53).
Prescribed fire or cultural burning as a tool for ecosystem
management had been used for millennia by Native Americans; with the
colonization of North America, Europeans introduced a culture of fire
suppression onto the landscape (Marks-Block et al. 2021, p. 3).
Wildfire suppression is still the dominant management practice over
prescribed or controlled burning across much of western North America
(Stephens et al. 2019, p. 391). Between 2017 and 2020, approximately
49,000 ha (120,000 ac) per year were treated with prescribed burning
across Federal, State, and Tribal lands in California (Gabbert 2022,
entire). The State of California recently released a report outlining a
plan to increase the use of ``beneficial fire'' to 162,000 ha (400,000
ac) annually by 2025 (California Wildfire & Forest Resilience Task
Force 2022, p. 3). Spotted owls can persist in low- and moderate-
severity fire areas with similar probabilities to unburned landscapes
(Roberts et al. 2011, p. 617), demonstrating their adaptation to a
natural fire regime (Verner et al. 1992, pp. 247-248; Stephens et al.
2019, p. 394). However, studying the relationship between spotted owls
and prescribed fire alone is difficult because there are usually
confounding factors of past timber harvest or salvage logging (Clark et
al. 2012, p. 15). Prescribed ``ecologically beneficial'' fire is an
important tool for protecting nesting and roosting habitat from
catastrophic fires and for maintaining diverse California spotted owl
habitat throughout the landscape (Roberts et al. 2011, p. 617; Stephens
et al. 2019, p. 394).
Fuels reductions and forest management practices within the
California spotted owl's range include clearcutting, mechanical
thinning, salvage logging, and prescribed fire. Depending on the method
used and how it is implemented, fuels reductions and forest management
practices can have both positive and negative influences on the
species. The existing regulatory mechanisms and conservation measures
do not completely ameliorate the negative impacts of fuels reductions
and forest management practices to California spotted owls; however,
land management direction, including the Sierra Nevada Forest Plan
Amendment, includes protective standards and guidelines that must be
adhered to while conducting management activities in California spotted
owl habitat.
Fuels reduction in some form is necessary to ensure California
spotted owl habitat persistence because long-term gains in habitat
protection outweigh the short-term negative effects, especially when
conservation measures are implemented appropriately (Jones et al.
2021a, p. 2; Jones et al. 2021b, entire; North et al. 2022, entire;
Safford et al. 2022, entire). Differences in forest management may help
explain why California spotted owl populations occurring in some mixed
ownership landscapes have higher occupancy, density, and probability of
reproduction compared to public land (Roberts et al. 2017, p. 113;
Hobart et al. 2019, p. 198; SPI et al. 2022, pp. 9, 17). The need to
increase the pace and scale of fuels reduction efforts is recognized
across agencies, and, recently, the Department of the Interior
announced funding through the Bipartisan Infrastructure Law
(Infrastructure Investment and Jobs Act, Pub. L. 117-58, 135 Stat. 429)
to increase fuels treatments across the United States (DOI 2022,
entire). The USFS also identified preliminary projects to address fuel
reduction projects through its wildfire crisis landscape investments,
and two projects are expected in the near term within the California
spotted owl's range that include mechanical thinning and prescribed
fire (Tahoe National Forest and the Stanislaus National Forest; USFS
2022a, entire). Fuels reductions and forest management practices will
likely continue to have varied effects on California spotted owls
throughout the species' range.
Competition and Hybridization With Barred Owls
The barred owl is a closely related species to the spotted owl,
native to eastern North America (Mazur and James 2000, ``Introduction''
section). Since the 1960s, the barred owl has been extending its range
westward, first coming in contact with northern spotted owls and more
recently moving into the California spotted owl's range (Peterson and
Robins 2003, p. 1162; Livezey 2009, p. 49; Keane et al. 2018, p. 5).
Barred owls were first detected in northwestern California in 1982
(Evens and LeValley 1982, p. 890), the Sierra Nevada in 1991 (Dark et
al. 1998, p. 53), and along the coast as far south as Marin County in
California by 2002 (Jennings et al. 2011, p. 105).
Barred owls and spotted owls have similar habitat requirements,
with old forests representing high-quality habitat for both, although
barred owls use a broad mix of forest types (Wiens et al. 2014, pp. 14,
32). Because barred owls have more habitat flexibility than spotted
owls, there is potential for barred owls to expand into spotted owl
habitat through corridors of lower quality habitat. For example, recent
barred owl sightings from Davis, California (eBird 2022, entire),
suggest that barred owls could expand across the Central Valley into
California spotted owl habitat from the west in addition to the more
likely pathway through forests in the Sierra Nevada. Although the
California spotted owl's range has a gap between the Sierra Nevada DPS
and the Coastal-Southern California DPS, barred owls may be able to
colonize the coastal-southern California spotted owl's range because of
the barred owl's ability to use other forest types. Detections of
barred owls in coastal forests in the Santa Cruz Mountains in San Mateo
County, California, an area without known occurrences of the California
spotted owl, suggests a pathway towards connectivity to the coastal
portion of the California spotted owl's range.
Barred owls are aggressively outcompeting and displacing spotted
owls on the landscape (Wiens et al. 2014, p. 1; Guti[eacute]rrez et al.
2017, p. xvi; Long and Wolfe 2019, entire). Barred owls are larger than
spotted owls (Guti[eacute]rrez et al. 2007, pp. 185-186) and
behaviorally dominant (Van Lanen et al. 2011, pp. 2197-2198). Although
diet overlaps between the two species, with both predominantly feeding
on nocturnal mammals, barred owls are generalists that consume many
more prey species in comparison to spotted owls (Wiens et al. 2014, pp.
24-25; Kryshak et al. 2022, pp. 12-13).
Competition between the two species results in negative effects to
the survival, productivity, and recruitment of northern spotted owls
(Dugger et al. 2016, pp. 69-91), and barred owls have been described as
demographically superior to northern spotted owls because they have
higher survival estimates and produced, on average, 4.4 times more
young than northern spotted owls over a 3-year period (Wiens et al.
2014, p. 28). The presence of barred owls has caused lower detection
rates and occupancy probabilities in northern spotted owls (Olson et
al. 2005, p. 918; Crozier et al. 2006, p. 760; Kroll et al. 2010, p.
1264; Yackulic et al. 2012, p. 1953; Yackulic et al. 2014, p. 265).
Although there is some evidence that lower detection rates may be in
part due to northern spotted owls responding less frequently in the
presence of barred owls (Crozier et al. 2006, p. 760), the negative
effects of barred owls on spotted owls are clear.
Although there is no evidence of barred owls wounding or killing
northern spotted owls (Wiens et al. 2014, p. 33), competition
ultimately has
[[Page 11619]]
population-level effects because of impacts to occupancy and
reproduction. Additionally, barred owls can hybridize with spotted owls
(Guti[eacute]rrez et al. 2017, p. 211). There are likely broader
impacts on the ecosystem from the barred owl's range expansion, such as
an imbalance in predator/prey relationships, causing even greater
impacts to spotted owl interspecific competition (Holm et al. 2016, p.
615). Because of the wide and diverse diet of barred owls in comparison
to spotted owls, barred owls will not be ecological replacements to the
spotted owls that they displace, and this could have widespread
ecological impacts (Kryshak et al. 2022, pp. 15-16).
Barred owl detections within the California spotted owl's range
have continued to increase. From 1989 to 2013, 51 barred owls and 27
barred owl/spotted owl hybrids had been detected in the Sierra Nevada
(Guti[eacute]rrez et al. 2017, p. xxv). By 2017, the number of barred
and barred owl/spotted owl hybrid detections in the Sierra Nevada
increased to approximately 145 (Keane et al. 2018, p. 7), with another
2.6-fold increase between 2017 and 2018 (Wood et al. 2020, p. 4). Even
these seemingly low numbers of barred owls in the California spotted
owl's range are of concern, given that in the northern spotted owl's
range, replacement of northern spotted owls began at a slow rate in the
early years of the expansion, followed by a rapid rate of replacement
once the barred owl population reached a critical mass (Forsman in
litt. 2018, p. 1). As shown, over the last 10 years in particular,
barred owl detections throughout the California spotted owl's range
have increased at a higher rate (Service 2022, figure 11).
Experimental barred owl removal studies were first initiated and
are currently ongoing in the northern spotted owl's range (e.g., Diller
et al. 2012, entire; Wiens et al. 2020, entire). In Washington and
Oregon, removals successfully decreased site use by barred owls and
increased northern spotted owl use within treatment areas (Wiens et al.
2021, entire). Further, successful barred owl removals can result in
competitive release for spotted owls (Wiens et al. 2021, pp. 4-5)
(competitive release describes a situation in which one of two similar
species competing for the same resources is removed, allowing the
remaining species to use more of the resources; this is generally
considered beneficial for the remaining species). In another (smaller)
example of barred owl removals within the northern spotted owl's range,
after nine barred owls were removed from historical northern spotted
owl sites, all sites were re-occupied by northern spotted owls within a
year of removal: four by the original residents and five by new
residents (Diller et al. 2012, p. 405). However, barred owls again
replaced the northern spotted owls at three sites within 1-4 years of
the northern spotted owls reoccupying those territories (Diller et al.
2012, p. 405). Overall, evidence to date indicates some measure of
success for northern spotted owls related to barred owl removal efforts
in at least some cases. However, species experts caution that forest
conditions, densities of barred owls, and numbers of spotted owls would
all factor into whether or not similar results could be obtained in
other areas (Wiens et al. 2020, p. 1).
Experimental barred owl removal studies have also recently been
initiated in the California spotted owl's range, specifically in the
Sierra Nevada (Hofstadter et al. 2022, entire). In 2017, a California
spotted owl conservation assessment concluded that control measures for
barred owls in the California spotted owl's range were likely to be
more successful and cost efficient while densities of barred owls are
still relatively low in the California spotted owl's range, and that if
control measures were not taken, barred owls would most likely replace
California spotted owls on the landscape in the future (though the
timescale of this replacement was uncertain) (Guti[eacute]rrez et al.
2017, pp. xxxi, xxv; see also Wood et al. 2020, pp. 5-7). Within the
California spotted owl's range, barred owl removal experiments were
initiated in 2018, and have continued through 2022 (Hofstadter et al.
2022, entire). Between 2018 and 2020, researchers removed 76 owls (63
barred owls and 13 hybrids) from the Sierra Nevada, decreasing barred
owl occupancy by a factor of 6.3 down to 0.03 (confidence interval:
0.01-0.04). Experimental removals were guided by passive acoustic
monitoring, which was also used to measure the efficacy of removals.
Partnerships were crucial to the regional-scale removal, with public-
private partnerships allowing access to 92 percent of the California
spotted owl's range in the Sierra Nevada, including almost all known
barred owls in the area and minimizing refugia for barred owls.
California spotted owls rapidly colonized territories where barred owls
were removed: 15 out of 27 territories were recolonized by California
spotted owls within 1 year of barred owl removals, with successful
breeding documented in five of these territories (Hofstadter et al.
2022, pp. 4-5). Early and effective experimental removals of barred
owls within the California spotted owl's range in the Sierra Nevada has
dampened the urgency of this threat, but the potential for continued
and persistent expansion into the range remains. Funding is currently
available to continue barred owl removal experiments in the California
extent of the Sierra Nevada through 2024 (Peery in litt. 2022).
However, continued barred owl monitoring and experimental removal would
likely need to continue into the future (Hofstadter et al. 2022, p. 6).
Management options are currently being evaluated for potential future
implementation.
Regulatory mechanisms and management actions that are providing or
could potentially provide some protection from the effects of barred
owl expansion include management teams, management plans, and habitat
conservation plans (HCPs) that coordinate, fund, and implement the
experimental removals described above. However, barred owls are a
significant threat to the persistence of California spotted owls, and
we expect the magnitude of the threat to increase into the foreseeable
future, particularly if management efforts are not continued.
Rodenticides
Exposure of nontarget wildlife to anticoagulant rodenticides
threatens many species, including California spotted owls, likely
because of ingestion of exposed prey animals, known as secondary
exposure (Gabriel et al. 2018, p. 5; Franklin et al. 2018, p. 2).
Secondary exposure to anticoagulant rodenticides in predators such as
raptors can be lethal, with higher levels causing severe blood loss and
internal hemorrhaging that can result in organ failure and death (Gomez
et al. 2022, p. 147). Although this threat has potential impacts to
individuals, the loss of just a few individuals may reduce survival and
the population growth rate because the California spotted owl is a
long-lived species with low reproductive rates. This threat would be
particularly detrimental if a parent were exposed during the breeding
season because hatchlings and juveniles rely on parental care to
survive, so the loss of just one parent would likely result in the loss
of offspring as well.
Rates of mortality in free-living wild birds due to anticoagulant
rodenticides are often unknown due to the difficulty of linking
exposure to death and the lack of understanding of toxicity thresholds
in different species (Gomez et al. 2022, pp. 147-148). Documentation of
anticoagulant
[[Page 11620]]
rodenticides in ovaries of female barred owl suggests the possibility
for in-utero transfer to chicks (Hofstadter et al. 2021, pp. 7-8). Sub-
lethal effects of anticoagulant rodenticides in other owl species
include reduced clutch size, brood size, fledging success, slower
clotting time, residual transfer to eggs, anemia, and impaired
mobility; however, these impacts have not yet been documented in
spotted owls (Rattner et al. 2012, p. 832; Salim et al. 2014, p. 113;
Gabriel et al. 2018, p. 7; Gomez et al. 2022, p. 148).
Although there is little information specific to California spotted
owls regarding the exposure rates and resulting impacts of
rodenticides, available literature on other species suggests the
potential for widespread exposure. Exposure of nontarget species to
anticoagulant rodenticides is commonly associated with agricultural or
urban settings, but exposure in forest settings in northern California
is detrimental to northern spotted owls and barred owls (Gabriel et al.
2018, p. 5; Franklin et al. 2018, p. 2). Seven out of 10 northern
spotted owl carcasses tested positive for anticoagulant rodenticides,
and 40 percent of 84 barred owls tested in the northern spotted owl's
range had been exposed (Gabriel et al. 2018, pp. 4-5). In another study
using barred owls as a proxy for spotted owls, almost half of barred
owls sampled (n=40) and one northern spotted owl sampled demonstrated
exposure to anticoagulant rodenticides (Wiens et al. 2019, p. 4). High
rates of exposure were also demonstrated in barred owls and barred owl/
spotted owl hybrids in California, with females having higher rates of
exposure than males (Hofstadter et al. 2021, pp. 6-7). Large amounts of
rodenticides and other pesticides have been found on USFS land in the
southern Sierra Nevada (Thompson et al. 2013, pp. 95-99). Approximately
85 percent of fisher (Martes pennanti--a carnivorous predator with
similar habitat requirements as California spotted owls) carcasses
tested in the Sierra National Forest had been exposed to rodenticides
(Gabriel et al. 2012, pp. 1-14; Thompson et al. 2013, pp. 91).
Anticoagulant rodenticide use has increased throughout California
with increases in illegal marijuana cultivation, as anticoagulant
rodenticides are used to control rodent damage to the plants (Franklin
et al. 2018, p. 1). A comparison of marijuana cultivation site
likelihood with northern spotted owl suitable habitat found almost 50
percent overlap between the two (Wengert et al. 2021, p. 10). Although
the number of illegal marijuana growing operations within the
California spotted owl's range is unknown, considering the number of
illegal marijuana growing operations found throughout the State, there
are likely thousands within the California spotted owl's range (Gabriel
et al. 2012, pp. 12-13; Thompson et al. 2013, pp. 95-99; Gabriel et al.
2018, p. 6).
In 2014, the California Department of Pesticide Regulation
restricted the purchase, possession, and use of anticoagulant
rodenticides in the State to purchase and use by a certified pesticide
applicator with a permit issued by the county agricultural commissioner
in order to protect wildlife; however, anticoagulant rodenticides
associated with illegal marijuana grows are more likely the source of
contaminants. If illegal marijuana grows are found, State law
enforcement will shut the operations down, but there is currently no
standardized clean-up protocol and a limited amount of funding to
ensure removal of all rodenticides. Recently there has been an
increased effort to locate and shutdown illegal marijuana grows on
public lands in California called Operation Forest Watch (Department of
Justice 2018, entire). Overall, anticoagulant rodenticides are likely
affecting owls across their range, and we expect this threat will
continue into the foreseeable future.
Development
Anthropogenic land use (including both cultivation and development)
in California is expected to increase 28 percent by 2100 with a
projected 3 percent decrease in overall forest land cover (Sleeter et
al. 2017, pp. 1068, 1075). Urbanization is projected to be a primary
driver of land use and land cover change in California over this time
frame (Sleeter et al. 2017, p. 1076). Urban development is a threat
throughout the range of California spotted owls; however, the threat is
more substantial in the coastal and southern California population
(Sleeter et al. 2017, p. 1081, figures 6 and 7). A majority of
California spotted owl habitat occurs on public lands (approximately 71
percent of total range); therefore, this threat is primarily limited to
a small amount of private lands.
Southern California faces high development demands with specific
threats of wind farms and large reservoirs impacting connectivity
within the California spotted owl's range (Guti[eacute]rrez et al.
2017, pp. 253-254). Loss of riparian areas due to water diversion in
southern California has created barriers to dispersal among small
populations (Guti[eacute]rrez et al. 2017, pp. 253-254). The southern
California area of the California spotted owl's range is fragmented,
with low dispersal between populations, so more development could
further exacerbate fragmentation (LaHaye et al. 2001, p. 692;
Barrowclough et al. 2005, p. 1116; Guti[eacute]rrez et al. 2017, pp.
253-254).
In the Sierra Nevada, low- to mid-elevation development is
considered a threat to the California spotted owl and its habitat
(Verner et al. 1992, pp. 264-265). Low- and mid-elevation zones in the
Sierra Nevada continue to experience human population growth, which may
increase the demand for development. Fifty percent of known California
spotted owl sites on the west slope of the Sierra Nevada are considered
wildland-urban interface and may be vulnerable to further development
(Guti[eacute]rrez et al. 2017, p. 207). The northern Sierra Nevada is
expected to have a higher level of forest harvest compared to other
parts of the California spotted owl's range (Sleeter et al. 2017, p.
1081, figure 7). Overall, development is likely affecting owls across
their range, and we expect this threat will continue into the
foreseeable future.
Conservation Efforts and Regulatory Mechanisms
Mechanisms and actions related to the California spotted owl and
its habitat include State and Federal laws and regulations, federal
incidental take permits, and forest management on USFS lands. In this
proposed rule, we describe the key actions related to the California
spotted owl and its habitat. For a full description of all conservation
efforts and regulatory mechanisms, please see the SSA report (Service
2022, pp. 57-66).
The USFS has been a part of ongoing conservation efforts for
California spotted owls, including the 2004 Sierra Nevada Forest Plan
Amendment, which includes USFS land in the Lassen, Plumas, Tahoe,
Humboldt-Toiyabe, Eldorado, Stanislaus, Sierra, Inyo, and Sequoia
California spotted owl analysis units, and the 2005 Southern California
National Forest Land Management Plans, which includes the Los Padres,
Angeles, San Bernardino, and Cleveland California spotted owl analysis
units. In 2019, the Inyo National Forest completed its own land
management plan, and revised forest plans for the Sierra and Sequoia
National Forests are expected to be final in 2023 (Miller in litt.
2022). Once these plans are finalized, the Inyo, Sierra, Sequoia
National Forests will follow their individual plans and no longer
follow
[[Page 11621]]
the 2004 Sierra Nevada Forest Plan Amendment. All of these are
regulatory documents that provide conservation measures for California
spotted owls on USFS lands (USFS 2004, entire; USFS 2005, entire; USFS
2019a, pp. 43-47; USFS 2022b, pp. 59-68; USFS 2022c, pp. 59-68). The
main goals of these conservation efforts include protection and
management of California spotted owl activity centers and home range
core areas, increasing the frequency of large trees on the landscape,
and increasing structural habitat diversity. The goals relate to
increasing the condition of the species' ecological needs to increase
resiliency and provide conservation efforts related to the threats of
large-scale, high-severity fire; clearcutting; mechanical thinning; and
salvage logging.
The 2004 and 2005 USFS land management plans and the 2019 Inyo
National Forest and 2022 draft versions of the Sierra and Sequoia
National Forest plans maintain the designation of PACs for California
spotted owls, which encompass the best available 121 ha (300 ac) of
habitat in as compact of a unit as possible around a nest tree (USFS
2004, p. 37; USFS 2005, p. 109; USFS 2019a, p. 43; USFS 2022b, p. 61;
USFS 2022c, pp. 61-62). There are special considerations for any land
management activities or projects that may take place within a PAC.
Depending on the plan, management standards and guidelines include
conducting surveys during the planning process of vegetation treatments
where appropriate (i.e., in areas of suitable habitat for California
spotted owls), limiting activities to reducing surface and ladder fuels
through prescribed fire, limiting mechanical treatments to only allow
fuel reduction treatments in some wildland urban defense zones where
prescribed fire is not feasible, identifying maximum size of canopy
gaps created within California spotted owl territories, requiring a
limited operating period for when vegetation treatments can occur, and
limiting the impacts a vegetation treatment can have on a PAC per year
(USFS 2004, pp. 50-51, 54, 60-61; USFS 2005, pp. 7, 82-83; USFS 2019a,
pp. 43-47; USFS 2022b, pp. 63-68; USFS 2022c, pp. 63-68).
In addition to protections, the 2004 Sierra Nevada Forest Plan
Amendment and the 2022 version of the Sierra and Sequoia National
Forest Plans outline desired conditions for PACs and other large
habitat blocks within the home range that include at least two tree
canopy layers, dominant and co-dominant trees with average diameters of
at least 61 cm (24 in) dbh, at least 60 percent to 70 percent canopy
cover, some very large snags (greater than 114 cm (45 in) dbh), and
snag and course woody debris levels that are higher than average (USFS
2004, pp. 37, 39-40; USFS 2022b, pp. 60-61; USFS 2022c, pp. 60-61). As
discussed below, in April 2019, the USFS finalized a new California
spotted owl conservation strategy for the Sierra Nevada (USFS 2019b,
entire). The intention of the strategy is to be used for adaptive
management and to be incorporated into future forest plan updates,
although it is not legally enforceable and does not commit agency
action or inaction.
As described above in ``Fuels Reduction and Forest Management,''
there is disagreement about whether or not measures in these plans,
such as mechanical thinning, are beneficial or detrimental to
California spotted owls, and whether or not protections afforded to
PACs are sufficient to ameliorate impacts to California spotted owls
(John Muir Project of Earth Island Institute and The Wild Nature
Institute 2014, pp. 70-71, 98, 108; Sierra Forest Legacy and Defenders
of Wildlife 2015, pp. 39-40). However, a meta-analysis of California
spotted owl occupancy and forest management practices indicated that
mechanical thinning treatments that maintain canopy cover at 40 percent
or greater would not substantially reduce California spotted owl
occupancy, although canopy cover at 50 percent or above is more
strongly correlated with California spotted owl occupancy (Tempel et
al. 2016, pp. 761-762). Forest management practices from the 2004
Sierra Nevada Framework generally maintain at least 50 percent canopy
cover as well as large trees within PACs, and in the 2005 Southern
California plan, 40-50 percent canopy cover must be maintained. The
2019 Conservation Strategy also maintains a minimum of 50 percent
canopy cover within PACs (USFS 2019b, p. 28). Overall, PACs are
designated to preserve key habitat used by California spotted owls, and
some researchers have concluded that PACs are a key conservation tool
that should continue to be implemented (Berigan et al. 2012, pp. 300,
303). In contrast, other research has shown that PACs can be more
susceptible to the effects of high-severity fire due to the relatively
larger amounts of surface fuel (North et al. 2012, p. 395).
In April 2019, the USFS completed an updated California spotted owl
conservation strategy for the Sierra Nevada national forests (USFS
2019a, entire). The updated strategy includes new scientific
understanding since the 2004 Sierra Nevada Forest Plan Amendment and
will be incorporated into national forest land management plans as they
are updated in the coming years, in accordance with USFS regulations in
title 36 of the Code of Federal Regulations (CFR) at part 219. Until
the revised national forest land management plans can be completed, the
Pacific Southwest Region of the USFS sent a letter of direction to the
Sierra Nevada national forests on April 19, 2019, to provide guidance
on implementing the new conservation strategy in the interim (USFS
2019b, entire). The new conservation strategy gives direction for
increased pace and scale of ecological restoration to provide more
resilient habitat for California spotted owls, while simultaneously
continuing to protect the most important habitat attributes and areas
for California spotted owls.
The three main goals for the 2019 conservation strategy include:
(1) Maintain a well-distributed and stable California spotted owl
population across the Sierra Nevada by minimizing impacts from non-
habitat threats (such as barred owls and contaminants); (2) promote and
maintain well-distributed California spotted owl habitat by developing
key habitat elements and connectivity; and (3) promote California
spotted owl persistence by enhancing habitat resilience to multiple
disturbances, considering climate change. This increased habitat
resilience will lead to improved conditions on the landscape and
greater population resiliency. The new strategy provides adaptive
management and metrics for success in order to ensure the conservation
measures outlined in the plan are beneficial to California spotted
owls.
In addition to the conservation strategy, the USFS is planning to
implement a new monitoring plan using acoustic recording units to cover
the Sierra Nevada portion of the California spotted owl's range. The
goal is to use the information from the new monitoring plan to allow
the USFS to conduct a future California spotted owl occupancy modeling
effort to provide information over a larger portion of the California
spotted owl's range and allow greater potential for inference on broad-
scale effects of restoration and disturbance (USFS 2019c, pp. 14-15).
Elements of the strategy may entail some short-term, localized
reduction in occupancy. These elements allow for more forest management
flexibility in application of fuels reduction and other landscape
treatment projects as compared to the 2004 Sierra Nevada Forest Plan
Amendment both within PACs and on the landscape, as well as more
flexibility in the retirement of
[[Page 11622]]
PACs when they are no longer occupied. Additional flexibility in these
landscape treatments provides access to additional tools to maintain
and restore California spotted owl habitat (USFS 2019a, entire). We
anticipate that the short-term impacts that may occur for the purpose
of fuel reduction and forest health will be outweighed by the long-term
benefit as more sustainable and dynamic habitat is developed through
active management (USFS 2019a, p. 2).
On August 30, 2017, an MOU (hereafter referred to as the Fire MOU)
was signed by SPI, CAL FIRE, National Fish and Wildlife Foundation, and
the USFS, which will impact all lands from Lassen National Forest south
through Stanislaus National Forest. The purpose of the Fire MOU is to
document the agreement between the parties to coordinate on certain
actions to reduce the risk of large-scale, high-severity wildfire
through forest fuels reduction to benefit California spotted owl
conservation. This MOU involves establishing a strategic conservation
framework to help restore and protect areas where California spotted
owls are threatened by habitat degradation due to uncharacteristically
extensive and severe adverse fire effects. The Fire MOU is designed for
signatories to engage in collaborative landscape-level fuels and fire
risk reduction treatments to: (1) Minimize potential fire-related
impacts to California spotted owl activity centers on Federal, State,
and private lands; and (2) better coordinate implementation of fuels
reduction work on Federal, State, and private lands to maximize the
effectiveness of this work. Sites for fuels treatment are selected to
minimize risk to known occupied California spotted owl activity
centers. Measures associated with the Fire MOU include fire management
activities such as increased mechanical thinning that may benefit
California spotted owls by decreasing risk of large-scale, high-
severity fire. If mechanical thinning is planned with consideration of
the California spotted owl's habitat needs, there may be some negative
impacts, but these would be outweighed by reducing the risk of large-
scale, high-severity fire in California spotted owl activity centers
(Jones et al. 2016a, p. 305; Service 2017, pp. 24-25; Chiono et al.
2017, p. 1; Jones et al. 2021b, p. 6).
The USFS, SPI (a private corporation), and CAL FIRE manage forest
lands in California that are frequently adjacent to each other and have
ongoing programs to protect and enhance habitat for fish and wildlife.
On these lands, forest fuels are managed to reduce fire risk and its
potential impacts on wildlife species. Under State law, SPI has the
authority to participate in fire suppression on its own lands, while
CAL FIRE, contract counties, USFS, and other government agencies have
primary fire suppression responsibility for all Federal, State, and
private wildlands in California. The parties also have responsibilities
and interests in the inventory of their respective lands for species
recognized as endangered, threatened, proposed as endangered or
threatened, candidate, and sensitive species by the Federal or State
government. The parties also have responsibility and interest in the
development of appropriate protection measures for these species. Due
to these natural resource challenges, the Fire MOU parties believe it
is important to establish a coordinated, multi-stakeholder agreement to
help protect and enhance forest resources.
Though the Fire MOU was initially set to expire on December 2019,
an amendment was signed in April 2019 to extend the terms of the MOU
through December 2024. In March 2020, a new MOU that supersedes the
2017 MOU and 2019 amendment was signed by the same parties. An
amendment to the 2020 Fire MOU was signed in September 2020 to add a
number of new commercial forest landowners. The terms of the 2020 MOU
are effective through December 2024. The Service is actively engaged
with the signatory parties to discuss fuels reduction efforts and
associated monitoring.
Barred owls have expanded into western North America over the past
several decades, first through the Pacific Northwest and more recently
into the Sierra Nevada. The Service and the USFS are funding
researchers at the University of Wisconsin-Madison to carry out an
ongoing barred owl removal study. The project grant was signed in
August of 2018, and funding has been secured from the Service and
potentially University of Wisconsin-Madison through 2025 (Peery in
litt. 2022). The project addresses several key questions related to the
range expansion of barred owls in the Sierra Nevada and will inform the
development of a scientifically based barred owl management plan.
Specifically, this project: (1) Assesses the current distribution and
density of barred owls; (2) conducts experimental barred owl removals;
(3) tests for reductions in barred owl site occupancy rates; (4)
quantifies spatiotemporal patterns of barred owl recolonization; and
(5) characterizes barred owl dispersal into and within the Sierra
Nevada. This project takes place primarily in the northern and central
Sierra Nevada, including Lassen National Forest, Lassen National Park,
Plumas National Forest, Tahoe National Forest, Eldorado National
Forest, Yosemite National Park, and Sequoia-Kings Canyon National Park.
Additionally, on July 22, 2022, the Service published in the
Federal Register (87 FR 43886) a notice of intent to prepare an
environmental impact statement, initiating a 30-day public scoping
period seeking input on barred owl management in the northern spotted
owl's and California spotted owl's ranges. Preventative barred owl
management for California spotted owls will likely be considered in the
environmental impact statement. Northern spotted owls are the main
focus right now, but barred owls have expanded into northern California
into the California spotted owl's range and are expected to continue to
expand without continued management.
Currently, two HCPs include the California spotted owl. Habitat
conservation plans are planning documents required as part of an
application for an incidental take permit; they can apply to both
listed and non-listed species, including those that are candidates or
have been proposed for listing. They describe the anticipated effects
of the proposed taking; how those impacts will be minimized or
mitigated to the maximum extent practicable; and how the HCP is to be
funded.
Sierra Pacific Industries is the largest private forest land owner
in California, with approximately 744,621 ha (1,840,000 ac) of
timberland in northern California (SPI 2021, p. 1). Sierra Pacific
Industries' habitat conservation plan for both the northern spotted owl
and California spotted owl covers all areas on SPI-managed property
where covered activities will occur within the range of the two spotted
owl subspecies, which is more than 607,028 ha (1,500,000 ac) (SPI 2021,
p. 2). Covered activities under the HCP include timber operations and
other forest management activities. Major activities associated with
the HCP include growing, harvesting, and transporting timber; timber
stand regeneration and improvements; road and landing construction and
maintenance; fuel break construction and maintenance; and monitoring
and research (including for spotted owls) (Service 2020, p. 8).
Implementation of the HCP is not expected to result in direct injury or
mortality of California spotted owls due to the implementation of
conservation measures that will be implemented throughout the 50-year
permit term. These measures will support California spotted owl species
needs and address threats currently affecting the species,
[[Page 11623]]
including reducing the risk of catastrophic fire and eradication of
illegal marijuana plantations (Service 2020, pp. 10-13).
In 2015, SPI began studying barred owls via removal experiments. In
2018, the study was revised to include the following objectives: (1)
assess the genetic differentiation of barred owl populations across
northern and central California, (2) analyze allele frequency changes
on the front of the range expansion, (3) estimate the amount of spotted
owl-barred owl interbreeding (admixture) in each population, and (4)
identify what barred owls are preying on in California. These efforts
are ongoing, and SPI has committed to continue these efforts during the
term of the permit, as feasible. Ongoing research and monitoring
efforts for California spotted owls on SPI land have indicated that
some California spotted owl populations in mixed-ownership landscapes
have higher occupancy, density, and probability of reproduction
compared to California spotted owl populations on public land (Roberts
et al. 2017, p. 113; Hobart et al. 2019, p. 198; SPI et al. 2022, pp.
9, 17).
The Western Riverside County Multiple Species Habitat Conservation
Plan (MSHCP) is one of the largest habitat conservation plans in the
United States, covering 202,343 ha (500,000 ac). The California spotted
owl is currently listed as a ``species not adequately conserved'' under
the MSHCP until an MOU is executed with the USFS that addresses
management of California spotted owls on USFS lands. The MSHCP plan
area includes 21,901 ha (54,119 ac) of modeled habitat for California
spotted owls. If the MOU with the USFS is signed, the loss of 5,223 ha
(12,905 ac) (24 percent) of this modeled habitat is anticipated over
the 75-year permit term. With the low density of California spotted
owls in the plan area, loss of these 5,223 ha (12,905 ac) is not
anticipated to result in direct mortality of adult birds. However, loss
of foraging and nesting habitats to development will cause California
spotted owls in impacted areas to disperse in search of other habitats.
Thus, loss of breeding and foraging habitat may impact overall
population numbers of California spotted owls within the plan area over
the long term by reducing the number of areas suitable for use as
foraging and nesting sites (Service 2004, p. 449). In order to offset
these impacts, the MSHCP will conserve and manage 535 ha (1,321 ac) (2
percent) of modeled habitat for California spotted owls within
additional reserve lands. In total, 16,679 ha (41,214 ac) (76 percent)
of the modeled habitat for California spotted owls will be included in
the MSHCP conservation area. If the MOU with the USFS is signed,
additional monitoring and management would occur in habitat for
California spotted owls within USFS lands included in the MSHCP
conservation area.
Combined Impacts of Threats
The threats discussed above not only act independently, but also
interact with each other. It is important to assess the relationship
between threats because there may be new or exacerbated impacts that
are not considered when a threat is assessed alone. There are a vast
number of ways threats may be interacting with each other, but the SSA
report and this proposed rule only focus on what is currently most
relevant to the viability of the species.
For example, climate change intensifies the threats of large-scale,
high-severity fire; drought; and tree mortality, and it increases
interannual climate variability (Kadir et al. 2013, pp. 132, 137;
Stephens et al. 2018, p. 77). Development in wildland-urban interfaces
also increases the likelihood of large-scale, high-severity fire (Mann
et al. 2016, pp. 14-18). An increase of large-scale, high-severity
fires with changing climate conditions can lead to accelerated, fire-
facilitated conversion of forest edge to non-forested habitat (Parks et
al. 2019, pp. 1, 7). The impacts to the California spotted owl would
likely range from direct physiological impacts to indirect habitat and
prey impacts. The loss of trees due to high-severity fire, drought, and
tree mortality would likely lead to increased salvage logging on the
landscape, further reducing California spotted owl habitat.
Additionally, the expansion of barred owls outcompeting California
spotted owls in combination with timber harvest outside of PACs further
worsens the outlook for habitat availability. Spotted owls living near
the wildland-urban interface may be at a higher risk for exposure to
anticoagulant rodenticides, as is the case for barred owls and hybrids
(Hofstadter et al. 2021, p. 8).
Barred owls are moving south into the California spotted owl's
range, so the northern portion of the Sierra Nevada DPS will likely
experience a greater magnitude of this threat, and earlier in time.
Tree mortality is more concentrated in the Sierra Nevada DPS than other
parts of the landscape and may experience more significant impacts from
this threat. The threat of wildfire is of higher magnitude in the
Coastal-Southern California DPS. Considering the temporal, spatial, and
interactive components of all the threats together is important for
understanding the viability of California spotted owls throughout their
range now and into the future.
Current Condition
For our current condition analysis in the SSA report and this
proposed rule, we considered the status of the two populations of
California spotted owls: the Sierra Nevada population and the coastal-
southern California population. As described above in Background, to
analyze these populations in more detail, we further divided them into
analysis units; however, we recognize that these units do not function
independently, and in areas where the species' distribution is
continuous, like the Sierra Nevada population, impacts to one unit may
result in impacts to an adjacent unit. We assessed the condition of all
California spotted owls' ecological needs where information was
available for each analysis unit, including the demographic factors of
survival, fecundity, occupancy, and population growth, and habitat
components of large trees and canopy cover. In addition, because high-
severity fire has significant effects on the condition of habitat
within an analysis unit, we also incorporated results from our fire
analysis. For each population, we present an overview of the available
information on ecological conditions and threats across the entire
population, our analysis of the demographic factors and habitat
components within each analysis unit to determine current condition,
and a summary assessing population resiliency. In this proposed rule,
for each DPS, we then assess California spotted owl redundancy and
representation under the current condition analysis.
For detailed information on how we determined all demographic and
habitat scores, total scores for each population and analysis unit, and
uncertainties considered in the analysis, please see the SSA report
(Service 2022, pp. 70-77).
Sierra Nevada DPS Current Resiliency
Resiliency is the ability of a species to withstand stochastic
events, the normal year-to-year variations in both environmental
conditions and demographic conditions (Redford et al. 2011, p. 40).
Determined by the size and growth rate of the populations comprising
the species, resiliency can be evaluated to gauge the ability of a
species to weather the natural range of favorable and unfavorable
conditions.
Until recently, California spotted owls and suitable habitat were
relatively
[[Page 11624]]
well-distributed in the Sierra Nevada with few barriers to dispersal
(Guti[eacute]rrez et al. 2017, p. 94): as of 2017, an estimated 1.98
million ha (4.9 million ac) of suitable habitat for California spotted
owls were available in the Sierra Nevada, primarily on Federal lands
(Guti[eacute]rrez et al. 2017, pp. xx, 123). Of that land, 75 percent
is managed by the USFS, 7 percent is managed by the NPS, and 18 percent
is either privately owned or managed by other government agencies
(Guti[eacute]rrez et al. 2017, p. xx). However, recent large,
catastrophic fires have reduced available habitat and have likely
created new barriers for California spotted owl dispersal in this DPS.
Other barriers to dispersal include urban and suburban development,
large reservoirs, physiographic features such as non-forested or
unsuitable habitat or vegetation communities, or lack of riparian areas
to act as corridors through unsuitable extents (Guti[eacute]rrez et al.
2017, pp. 94-95, 253-254).
From our habitat analyses, we found that the Sierra Nevada has
higher canopy cover and tree size values than southern California
(Service 2022, tables 5, 9, and 13). When comparing the northern to the
southern Sierra Nevada, the north contains higher canopy cover, which
aligns with historical forest structure data that tend to show more
dense forests in the northern Sierra Nevada (Van Wagtendonk et al.
2006, p. 250), with the exception being on the east side of the Sierra
Nevada (Humboldt-Toiyabe and Inyo analysis units), which contains more
open and disjunct habitat than the west side. Higher canopy cover
combined with higher precipitation levels tend to result in lower tree
mortality in the northern Sierra Nevada, which may have helped reduce
the potential for megafires in the northern Sierra Nevada in past
years, but climate change impacts of reduced snowpack and increased
temperatures show that increased fire risk is also occurring in the
northern Sierra Nevada. We also found that the two units mostly
composed of National Parks (Yosemite and Sequoia-Kings Canyon) contain
the largest tree size percentages. Overall, the overlap values between
canopy cover and large trees were low across all analysis units
(Service 2022, table 9).
The threats that are currently impacting the Sierra Nevada
population include large-scale, high-severity fire; tree mortality;
drought; climate change; various impacts from fuels reductions and
forest management; competition with barred owls; and rodenticides.
These threats are not equivalent across all analysis units within the
Sierra Nevada population (Service 2022, pp. 77-87). For example,
competition with barred owls is more pronounced in the northern part of
this population than in the southern portion, and the threat from
rodenticides is more pronounced at the wildlife-urban interface.
However, some threats, like fire, are considered a threat across the
population, and there is a general increasing trend in the annual
acreage and relative proportion of high-severity fires in the Sierra
Nevada (Keane in litt. 2022, p. 3). In 2020-2021, the percent of
habitat that burned at high severity within California spotted owl PACs
in the Sierra Nevada was almost twice as that from 1993-2019; in 1993-
2019, 44 percent of habitat burned, with 35 percent of that at high
severity, compared to 65 percent of fire being high severity in 2020-
2021 (Keane in litt. 2022, p. 5).
We conducted a separate fire analysis for the entire California
spotted owl's range, which includes PACs as well as additional acreage
outside PACs (Service 2022, pp. 29-30, appendix I). Our fire analysis
shows similar results, with approximately 42 percent of the California
spotted owl's range in the Sierra Nevada burned between 1984 and 2021,
with 7 percent and 12 percent of that total from acreages burned in
2020 and 2021, respectively. Of the 42 percent of California spotted
owl's range burned within the Sierra Nevada, approximately 13 percent
was burned at high severity (Service 2022, appendix I). In our
supplemental analysis that analyzes habitat and fire metrics along an
ecological boundary between the northern and southern Sierra Nevada, we
found that both portions of the Sierra Nevada burned at similar amounts
between 1984 and 2021 (Service 2022, appendix I). However, the majority
of burned acreage in the northern Sierra Nevada occurred in 2021 (18
percent burned with 9 percent at high severity compared to 5 percent or
less in all other years and 2 percent or less at high severity from
1984 to 2021). In the southern Sierra Nevada, 11 percent burned in 2020
with 2 percent at high severity in 2020 and 2021, compared to 5 percent
or less total burned and 1 percent or less at high severity from 1984
to 2021 (Service 2022, appendix I). These results suggest higher levels
of disturbance to the species and increased recovery time for habitat
conditions to improve post-fire because such a large acreage burned
over a relatively concentrated period of time.
In addition to common threats acting on all analysis units within
this population, there are also common management actions taking place
within the Sierra Nevada population. For example, the USFS designates
PACs around known California spotted owl nest trees, so analysis units
containing national forests (e.g., all Sierra Nevada population
analysis units except for Yosemite and Sequoia-Kings Canyon) include
these protections. Further, barred owl removal experiments in the
northern Sierra Nevada have so far been successful in avoiding the
catastrophic impacts that could have occurred in the absence of any
management.
The current condition of analysis units throughout the Sierra
Nevada population varies, with three analysis units currently
considered stable, five declining, and three strongly declining
(Service 2022, table 12). All three of the units ranked as strongly
declining are on the upper boundary of our scoring system for the SSA
report. Based on these results, the overall condition of the Sierra
Nevada population is declining and, therefore, has low resiliency.
However, though resiliency has declined from historical conditions and
connectivity has decreased, the Sierra Nevada population is still
distributed throughout its historical range, and ongoing conservation
measures and regulatory mechanisms are decreasing the magnitude of
threats. Therefore, the Sierra Nevada population maintains the ability
to withstand stochastic events.
Sierra Nevada DPS Current Redundancy
To assess current redundancy of the Sierra Nevada DPS, we consider
the ability of a species to withstand catastrophic events, i.e.,
natural or anthropogenic stochastic events that would result in the
loss of a substantial component of the overall species population.
However, redundancy is not simply a measure of the total number of
individuals or populations of a species, but instead must also be
evaluated in the context of an assessment of reasonably plausible
catastrophic events. For example, when we consider the redundancy of an
entity comprised of a single population that is very large and widely
distributed, it could have a high ability to withstand a catastrophic
event that would only affect a small percentage of the overall
population. Therefore, our characterization of the Sierra Nevada DPS's
redundancy takes into consideration both an assessment of the size and
distribution of its population, and an evaluation of the kinds and
likelihood of reasonably plausible catastrophic events to which the
species could be exposed.
Of the two populations throughout the species' range, the Sierra
Nevada population that makes up the Sierra Nevada DPS covers the most
area and is
[[Page 11625]]
the largest population. Catastrophic events that could impact
California spotted owls include very large, high-severity wildfire;
extreme drought; extreme weather events; and prolonged and persistent
competition and displacement due to barred owl expansion. Overall,
current California spotted owl redundancy has declined from historical
condition, which risks making the species more vulnerable to
extirpations from catastrophic events. However, the Sierra Nevada DPS
is large, contiguous, and still distributed throughout its historical
range, meaning it is more able to recover from events such large,
catastrophic wildfires.
Sierra Nevada DPS Current Representation
In this proposed rule, to assess current representation, which is
the California spotted owl's current ability to adapt to change, we
considered the ecological setting and genetic diversity in the Sierra
Nevada DPS. In the Sierra Nevada population, a majority of California
spotted owls occur within mid-elevation ponderosa pine, mixed-conifer,
white fir, and mixed-evergreen forest types, with few California
spotted owls occurring in the lower elevation oak woodlands of the
western foothills (Guti[eacute]rrez et al. 2017, p. xix). Further,
California spotted owls in the northern portion of the Sierra Nevadas
tend to have larger home range sizes than California spotted owls in
the southern portion of the mountain range (Guti[eacute]rrez et al.
2017, p. xviii). Within the Sierra Nevada, the northern portion of the
range experiences more precipitation and lower mean temperatures than
the southern portion of the range (Climate Engine 2017, unpaginated).
The diversity in habitat and climate between and within the areas for
which we have data suggests that the species has some flexibility to
adapt to changing environmental conditions.
Of the three spotted owl subspecies (northern, California, and
Mexican), California spotted owls have the lowest genetic diversity
when measured by unique haplotypes (Barrowclough et al. 1999, pp. 919,
927; Haig et al. 2004, p. 683). This suggests that California spotted
owls have lower genetic representation in general than either of the
other two subspecies. However, whether the observed level of genetic
diversity indicates low representation is unclear. Because the
California spotted owl has persisted throughout much of its historical
range for an extended period of time, the relatively low genetic
diversity may be an historical artifact rather than an indication of
concern for representation. Within the California spotted owl
subspecies, genetic differences are found between California spotted
owls found in the Sierra Nevada and those found in coastal-southern
California; this provides some degree of genetic representation at the
subspecies level, although not enough for each population to be
considered a separate subspecies (Barrowclough et al. 1999, p. 927;
Guti[eacute]rrez et al. 2017, p. 101; Hanna et al. 2018, pp. 3946-3947,
3949). Whole-genome data indicate that there is greater genetic
difference between California spotted owls (in the northern and
southern extent of the subspecies' range) than there is between
northern spotted owls and California spotted owls in the northern
portion of the range; this is consistent with isolation-by-distance
(geographic differences increase with geographic scale) (Hanna et al.
2018, pp. 3946-3947). The genetic differences observed between
populations, as well as the habitat and climate differences, may
represent a moderate degree of adaptation and thus moderate
representation at the subspecies level.
Though the Sierra Nevada DPS has lower representation than the
subspecies as a whole, the California spotted owl continues to inhabit
different ecological settings throughout the Sierra Nevada. The overall
condition of the DPS has declined, which has likely resulted in reduced
genetic diversity. Therefore, current California spotted owl
representation in the Sierra Nevada DPS has declined from historical
condition, suggesting that the ability for the taxon to adapt to change
is decreased.
Coastal-Southern California DPS Current Resiliency
Habitat within the Coastal-Southern DPS is considered to be
naturally fragmented, with little dispersal occurring between
subpopulations due to discontinuous mountain ranges (Guti[eacute]rrez
et al. 2017, pp. 93-95). This natural fragmentation has been further
fragmented by development/habitat loss in the greater southern
California area. Specific information about habitat and demographic
conditions, when available, is incorporated below for each of our
southern California analysis units. The available evidence does not
document successful dispersal between the San Bernardino, San Gabriel,
and San Jacinto Mountains, which are adjacent mountain ranges,
indicating that if dispersal does occur within this population, it is
very rare (LaHaye et al. 2001, entire; LaHaye et al. 2004, entire;
Guti[eacute]rrez et al. 2017, pp. 242, 250).
As previously discussed, within this population, occupancy data are
only available for the San Bernardino Mountains. The San Bernardino
Mountains have historically contained the largest number of California
spotted owls, suggesting that information extrapolated from this area
would lead to a too optimistic view for the overall population
(Guti[eacute]rrez et al. 2017, p. 242). Data from one recent study
showed higher occupancy in the San Bernardino Mountains than the San
Jacinto and San Gabriel Mountains, and the authors suggest that other
parts of southern California may also have experienced greater declines
than this area (Tempel et al. 2022, pp. 20-21).
As mentioned for the Sierra Nevada population, our habitat analyses
found that habitat values for large trees and canopy cover were lower
in southern California than in the Sierra Nevada (Service 2022, tables
5, 9, and 13). Overlap between canopy cover and large trees was also
low (Service 2022, table 13). In southern California, high canopy cover
is positively associated with California spotted owl reproductive
output, but large trees appeared to be more important than high canopy
cover (Tempel et al. 2022, p. 22) and are also important for occupancy.
Our analysis found large tree values for southern California are low,
which may indicate lower habitat quality in this analysis unit. For
this population, we conducted an additional analysis identifying the
percentage of small trees within the overall population that could
potentially support platform or stick nests (Service 2022, table 14).
We found that 14 percent of the coastal-southern California analysis
units contain these small trees compared to an overall value of 1
percent for large trees only trees larger than 61 cm dbh are
considered. When looking at the combined total of small trees and large
trees, 16 percent of southern California contains potential trees that
could support the California spotted owl's ecological needs (Service
2022, table 14).
The threats that are likely currently impacting this population
include large-scale, high-severity fire; tree mortality; drought;
climate change; various impacts from fuels reductions and forest
management; and rodenticides. Competition with barred owls is not yet
considered a current threat within this population. Impacts from these
threats may not be equally distributed across the population and are
not equivalent to the ways that these threats impact the Sierra Nevada
population. For example, what might be considered a stochastic event
(in this case, an event that removes one or a few individuals from the
population) in the Sierra Nevada population could instead be considered
[[Page 11626]]
catastrophic if it were to occur in the coastal-southern California
population because of the lower number of California spotted owls
within this population. Our fire analysis shows that 60 percent of the
California spotted owl's range in southern California burned between
1984 and 2021, 17 percent at high severity, with 6 percent of the total
area burned in 2020 and 1 percent at high severity that year. There
were no fires in 2021 within the range of this population. Typically, 4
percent or less of habitat within this population burned per year, with
1 percent or less burning at high severity, although some years burned
at higher percentages (2003 at 6 percent with 3 percent high severity,
and 2007 at 8 percent with 4 percent high severity; Service 2022,
appendix I). In addition to common threats acting on all analysis units
within this population, there are also common management actions taking
place throughout the analysis units comprising the coastal-southern
California population. For example, analysis units containing national
forests include PACs around known California spotted owl nest trees.
The current condition of analysis units within the Coastal-Southern
California DPS is that two analysis units are strongly declining and
two units are declining (Service 2022, table 17). Based on these
results and our scoring of habitat conditions and available demographic
information (Service 2022, table 18), the overall condition of the
Coastal-Southern California DPS is strongly declining and, therefore,
has very low resiliency.
Coastal-Southern California DPS Current Redundancy
As with the Sierra Nevada DPS, our characterization of redundancy
for the Coastal-Southern California DPS takes into consideration both
an assessment of the size and distribution of its population, and an
evaluation of the kinds and likelihood of reasonably plausible
catastrophic events to which the species could be exposed.
As with the Sierra Nevada DPS, catastrophic events that could
impact the Coastal-Southern California DPS include very large, high-
severity wildfire; extreme drought; extreme weather events; and
prolonged and persistent competition and displacement due to barred owl
expansion. The population that makes up the Coastal-Southern California
DPS is highly fragmented with gaps between occupied areas. In areas
where demographic data are available (the San Bernardino analysis
unit), declines have accelerated over the last 30 years, and as stated
above, information extrapolated from a study area that historically
contained the largest number of California spotted owls could lead to
an overly optimistic view for other areas of the coastal-southern
California population (Guti[eacute]rrez et al. 2017, p. 242). Overall,
current California spotted owl redundancy in this DPS has declined from
historical condition, making the species more vulnerable to
extirpations and potentially extinction from catastrophic events.
Coastal-Southern California DPS Current Representation
To assess current representation, which is the California spotted
owl's current ability to adapt to change, we considered the ecological
setting and genetic diversity among the two California spotted owl
populations. In coastal and southern California, California spotted
owls are found in riparian/hardwood forests and woodlands, live oak/big
cone fir forests, and redwood/California laurel forests
(Guti[eacute]rrez et al. 2017, p. xxvi). California spotted owls use
stick nests more frequently in southern California compared to in the
Sierra Nevada. Further, California spotted owls in the northern portion
of the range tend to have larger home range sizes than California
spotted owls in the southern portion of the range (Guti[eacute]rrez et
al. 2017, p. xviii). The climate of the Coastal-Southern California DPS
is more arid than that of the Sierra Nevada (Climate Engine 2017,
unpaginated).
In regard to genetic diversity, in the Coastal-Southern California
DPS, the population has become highly fragmented, which likely has
resulted in reduced genetic diversity. The increased fragmentation has
reduced the amount of available habitat in throughout the coastal-
southern California population. Therefore, current California spotted
owl representation in the coastal-southern California population has
declined from historical condition, suggesting that the ability for the
DPS to adapt to change is decreased.
Future Condition
For our future condition analysis, we forecast the response of the
Sierra Nevada DPS of the California spotted owl to two plausible future
scenarios. These two scenarios represent the extremes of a range of
future changes in environmental conditions and success of implemented
conservation efforts. The future scenarios project the influences to
viability discussed above in Current Condition into the future and
consider the impacts those influences would potentially have on
California spotted owl viability. We apply the concepts of resiliency,
redundancy, and representation to the future scenarios to describe the
future viability of California spotted owls in the Sierra Nevada DPS.
For this analysis, we describe two future scenarios and assess
future resiliency for the Sierra Nevada DPS. Scenario 1 assesses future
viability with an increase in the trend and magnitude of threats with
implemented management efforts having mixed success. Scenario 2
assesses the viability of the species if the trend and magnitude of
threats were to continue at the current trajectory into the future with
implemented management efforts
[…truncated; see source link]Indexed from Federal Register on February 23, 2023.
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