                      FOR PUBLICATION

         UNITED STATES COURT OF APPEALS
             FOR THE NINTH CIRCUIT

 CENTER FOR BIOLOGICAL                               No. 14-17513
 DIVERSITY; MARICOPA AUDUBON
 SOCIETY,                                              D.C. No.
               Plaintiffs-Appellants,               2:12-cv-02296-
                                                         DGC
                      v.

 RYAN ZINKE, in his official capacity                  OPINION
 as Secretary of the U.S. Dept. of the
 Interior; GREG SHEEHAN, in his
 official capacity as Acting Director,
 U.S. Fish and Wildlife Service,
                 Defendants-Appellees.

        Appeal from the United States District Court
                 for the District of Arizona
        David G. Campbell, District Judge, Presiding

           Argued and Submitted February 13, 2017
                  San Francisco, California

                      Filed August 28, 2017

  Before: William A. Fletcher and Johnnie B. Rawlinson,
   Circuit Judges, and Robert W. Pratt,* District Judge.

                  Opinion by Judge W. Fletcher


    *
      The Honorable Robert W. Pratt, United States District Judge for the
Southern District of Iowa, sitting by designation.
2         CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

                            SUMMARY**


                     Endangered Species Act

    The panel affirmed the district court’s summary judgment
in favor of the U.S. Fish and Wildlife Service (“FWS”) in an
action brought by plaintiff environmental groups challenging
the FWS’s determination that the Sonoran Desert Area bald
eagle was not a distinct population segment eligible for listing
under the Endangered Species Act.

   In order to qualify as “distinct,” the population segment
must be both discrete and significant. The parties agreed that
the desert eagle population was discrete, and disputed
whether the population was significant.

    The panel rejected plaintiffs’ contention that the FWS
acted arbitrarily and capriciously in concluding in 2012 that
the desert eagle population segment was not significant
within the meaning of the distinct population segment policy.
Specifically, the panel held that FWS reasonably concluded
that, while the combination of unusual characteristics in a
discrete population was sufficient to satisfy the persistence
factor, those characteristics did not by themselves necessarily
require a conclusion that the desert eagle population segment
was ecologically or biologically significant for the bald eagle
taxon as a whole. The panel further held that the FWS
reasonably concluded that if the desert eagle population
segment were “extirpated,” this could not create a significant
gap in the range of the taxon. Finally, the panel held, contra

    **
       This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE               3

to plaintiffs’ contention, that the FWS directly addressed
climate change in its 2012 decision.


                         COUNSEL

Daniel J. Rohlf (argued), Earthrise Law Center, Portland,
Oregon; Justin Augustine, Center for Biological Diversity,
Oakland, California; for Plaintiffs-Appellants.

Mark R. Haag (argued), David C. Shilton, H. Hubert Yang,
and Kristen L. Gustafson, Attorneys; John C. Cruden,
Assistant Attorney General; Environment & Natural
Resources Division, United States Department of Justice,
Washington, D.C.; Frank Lupo, Office of the Solicitor,
Southwest Region, United States Department of the Interior,
Albuquerque, New Mexico; for Defendants-Appellees.


                         OPINION

W. FLETCHER, Circuit Judge:

    Plaintiffs-Appellants Center for Biological Diversity and
Maricopa Audubon Society (collectively “CBD”) challenge
the determination of the U.S. Fish and Wildlife Service
(“FWS”) that the Sonoran Desert Area bald eagle (“desert
eagle”) is not a distinct population segment (“DPS”) eligible
for listing under the Endangered Species Act. FWS and the
National Marine Fisheries Service have promulgated a policy
statement to guide determinations whether a particular
population segment qualifies as distinct. In order to qualify
as distinct, the DPS must be both discrete and significant.
Inter alia, the policy statement provides a non-exhaustive list
4       CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

of criteria for determining whether a population segment is
“significant.” CBD argues that if one of the criteria is
satisfied, FWS is compelled to conclude that the population
segment is significant. CBD argues, further, that FWS
improperly ignored the desert eagle’s status as a peripheral
population, and that FWS failed to evaluate the significance
of climate change. We disagree with these arguments and
affirm the decision of the district court.

                       I. Background

    The bald eagle was first listed as an endangered species
in 1967, under a predecessor to the Endangered Species Act
(“ESA”). See Endangered Species Preservation Act of 1966,
Pub. L. 89-669, 80 Stat. 926. In 1978, after the passage of the
ESA, the bald eagle was listed as endangered in forty-three
states and listed as threatened in an additional five states.
43 Fed. Reg. 6230, 6230 (Feb. 14, 1978). In 1995, the bald
eagle was listed as threatened in the lower forty-eight states.
60 Fed. Reg. 36000, 36000 (July 12, 1995).

    In 1963, there had been an estimated 487 breeding pairs
of bald eagles in the United States. 72 Fed. Reg. 37346 (July
9, 2007). In 2007, there were an estimated 9,789 breeding
pairs. Id. As a result of this remarkable recovery, FWS
removed the bald eagle from the list of threatened species in
2007. Id. The delisting does not affect the protection that
continues to be provided under the Bald and Golden Eagle
Protection Act, 16 U.S.C. § 668, and the Migratory Bird
Treaty Act, 16 U.S.C. § 703. In 2004, while delisting of the
bald eagle was being considered, CBD filed a petition asking
FWS to list the Sonoran Desert Area bald eagle as a DPS.
FWS denied the petition. This litigation followed.
         CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE               5

    The desert eagle population includes “all bald eagle
territories within Arizona, the Copper Basin breeding area in
California near the Colorado River, and the territories of
interior Sonora, Mexico, that occur within the Sonoran Desert
and adjacent transitional communities.” 77 Fed. Reg. 25792,
25792 (May 1, 2012). In its initial response to CBD’s
petition, FWS found in 2006 that the desert eagle did not
“constitute[ ] a valid DPS.” 71 Fed. Reg. 51549, 51556 (Aug.
30, 2006). CBD challenged this finding in the district court,
and the court set it aside as arbitrary and capricious. Ctr. for
Biological Diversity v. Kempthorne, 2008 WL 659822 (D.
Ariz. Mar. 6, 2008). The court concluded that there was
evidence that FWS officials in Washington, D.C. had given
“marching orders” to FWS field personnel to deny the
petition. Id. at *12. The court remanded the petition to FWS
with directions to conduct a full status review. Id. at *15–16.

    In 2010, FWS again found that the desert eagle population
did not constitute a DPS. 75 Fed. Reg. 8601, 8620 (Feb. 25,
2010). CBD again challenged the finding, and the district
court again remanded to FWS. See Ctr. for Biological
Diversity v. Salazar, 2011 WL 6000497, at *14 (D. Ariz Nov.
30, 2011). The court found that FWS’s 2007 delisting
procedure “failed to comport with the notice, comment, and
consultation requirements of the law.” Id. at *9. The court
ordered FWS to make a new finding based on information
gathered during the status review. Id. at *14.

    In 2012, FWS found for a third time that the desert eagle
did not constitute a DPS. 77 Fed. Reg. at 25792, 25828 (May
6        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

1, 2012). CBD again challenged FWS. In a careful and
thorough opinion, the district court granted summary
judgment to FWS.

    CBD timely appealed.

                   II. Standard of Review

    We review the district court’s grant of summary judgment
de novo. Biodiversity Legal Found. v. Badgley, 309 F.3d
1166, 1175 (9th Cir. 2002). Review of agency decisions
under the ESA is governed by the Administrative Procedure
Act (“APA”). Greater Yellowstone Coal., Inc. v. Servheen,
665 F.3d 1015, 1023 (9th Cir. 2011). An agency action can
be overturned when arbitrary, capricious, an abuse of
discretion, or otherwise not in accordance with law. Id. An
agency action must be reversed when the agency has “relied
on factors which Congress has not intended it to consider,
entirely failed to consider an important aspect of the problem,
offered an explanation for its decision that runs counter to the
evidence before the agency, or is so implausible that it could
not be ascribed to a difference in view or the product of
agency expertise.” Pac. Coast Fed’n of Fishermen’s Ass’ns
v. Nat’l Marine Fisheries Serv., 265 F.3d 1028, 1034 (9th Cir.
2001) (quoting Motor Vehicle Mfrs. Ass’n v. State Farm Mut.
Auto. Ins. Co., 463 U.S. 29, 43 (1983)). A court cannot
substitute its judgment for that of the agency. Greater
Yellowstone Coal., Inc., 665 F.3d at 1023. “The only
question before us is whether the Service, in reaching its
ultimate finding, ‘considered the relevant factors and
articulated a rational connection between the facts found and
the choices made.’” Nw. Ecosystem Alliance v. U.S. Fish &
Wildlife Serv., 475 F.3d 1136, 1145 (9th Cir. 2007) (quoting
        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE              7

Nat’l Ass’n of Home Builders v. Norton, 340 F.3d 835, 841
(9th Cir. 2003)).

                       III. Discussion

    The ESA requires FWS to identify and list species that are
“endangered” or “threatened.” 16 U.S.C. § 1533. An
interested person may petition FWS to add to or remove from
the list a particular species. § 1533(b)(3)(A). Upon receiving
such a petition, FWS must promptly determine whether the
petition is supported by “substantial scientific or commercial
information.” Id. If so, FWS must “commence a review of
the status of the species concerned.” Id. FWS is required to
make a finding on the status of the species within twelve
months and publish its finding in the Federal Register.
§ 1533(b)(3)(B). FWS must make its decision “solely on the
basis of the best scientific and commercial data available.”
§ 1533(b)(1)(A). If FWS finds that a petitioned action is
warranted, it must promptly publish a proposed regulation to
implement its finding. § 1533(b)(3)(B)(ii).

    “Species” is defined to include “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.” § 1532(16). The ESA does not define the term
“distinct population segment.” FWS and the National Marine
Fisheries Service, the two agencies charged with
implementing the ESA, have jointly promulgated a policy
statement to guide determinations whether DPS status is
warranted. See Policy Regarding the Recognition of Distinct
Vertebrate Population Segments Under the Endangered
Species Act, 61 Fed. Reg. 4722 (Feb. 7, 1996) (“DPS
Policy”). We have previously determined that “the DPS
Policy is a reasonable construction of ‘distinct population
8        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

segment’” and “is entitled to Chevron deference.” Nw.
Ecosystem Alliance, 475 F.3d at 1141–45.

     The DPS Policy sets forth two requirements for DPS
status: the “[d]iscreteness of the population segment in
relation to the remainder of the species to which it belongs,”
and the “significance of the population segment to the species
to which it belongs.” 61 Fed. Reg. at 4725. “Discreteness”
is satisfied if a population segment is “separated from other
populations of the same taxon as a consequence of physical,
physiological, ecological, or behavioral factors,” or if a
population’s boundaries are marked by international borders.
Id. “Significance” is determined using, inter alia, four
factors listed below. Id. A population qualifies as a DPS if
it is both discrete and significant. Id. If a population is found
to be a DPS, the inquiry proceeds to whether it is endangered
or threatened. Id. The parties agree that the desert eagle
population is discrete, and that it therefore satisfies the first
of the two criteria for achieving DPS status. They dispute
whether the population is significant.

    The DPS Policy provides in relevant part:

        Significance: If a population segment is
        considered discrete . . . , its biological and
        ecological significance will then be
        considered in light of Congressional guidance
        . . . that the authority to list DPS’s be used
        “ * * * sparingly” while encouraging the
        conservation of genetic diversity. In carrying
        out this examination, the Services will
        consider available scientific evidence of the
        discrete population segment’s importance to
        the taxon to which it belongs.            This
         CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE          9

        consideration may include, but is not limited
        to, the following:

           1. Persistence of the discrete population
        segment in an ecological setting unusual or
        unique for the taxon,

            2. Evidence that loss of the discrete
        population segment would result in a
        significant gap in the range of a taxon,

           3. Evidence that the discrete population
        segment represents the only surviving natural
        occurrence of a taxon that may be more
        abundant elsewhere as an introduced
        population outside its historic range, or

           4. Evidence that the discrete population
        segment differs markedly from other
        populations of the species in its genetic
        characteristics.

            Because precise circumstances are likely
        to vary considerably from case to case, it is
        not possible to describe prospectively all the
        classes of information that might bear on the
        biological and ecological importance of a
        discrete population segment.

Id. (“* * *” elision in original).

    FWS concluded in 2012 that the desert eagle population
segment is not significant within the meaning of the DPS
Policy. On appeal, CBD argues on three grounds that FWS
10      CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

acted arbitrarily and capriciously in reaching that conclusion:
(1) in addressing the first significance factor, FWS properly
concluded that the desert eagle population was persistent in
its unusual or unique ecological setting, but improperly
concluded that it was not significant despite its qualification
under this factor; (2) in addressing the second significance
factor, FWS improperly concluded that the loss of the desert
eagle population would not create a significant gap in the bald
eagle population as a whole, ignoring the importance of
peripheral populations; and (3) in evaluating the significance
of the desert eagle population to the bald eagle population as
a whole, FWS improperly failed to consider the impact of
climate change. We consider, and reject, these arguments in
turn.

          A. Persistence in an Ecological Setting
             Unusual or Unique for the Taxon

     FWS concluded that the desert eagle population segment
satisfied the persistence factor of the DPS Policy, but
nonetheless concluded that the population did not satisfy the
significance requirement. 77 Fed. Reg. at 25806–08. CBD
argues that if FWS finds that a population segment satisfies
any of the four listed significance factors, it is required to
conclude that the population segment is significant. CBD
frames the question as follows: “FWS’ interpretation of its
DPS Policy thus poses a very clear question for this Court:
May FWS determine that a population meets one of the DPS
Policy’s express indicators of ‘significance’ and nonetheless
still find that the population is not significant within the
meaning of the Policy?” Our answer to CBD’s question is
“yes.”
        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE              11

   In evaluating the desert eagle population’s persistence,
FWS provided an extensive analysis of the ways in which the
desert eagle’s ecological setting is unusual or unique, and the
ways in which the desert eagle has responded to that setting.
FWS noted at the beginning of its analysis:

       Bald eagles are highly adaptable, wide-
       ranging habitat generalists. Across the range
       of the species, there is no “usual” ecological
       setting, in terms of the elevation, temperature,
       prey species, nest tree species, or type of
       water source, for the taxon. The bald eagle is
       capable of inhabiting areas throughout North
       America, so long as a sufficient food source
       persists.

77 Fed. Reg. at 25806. FWS concluded that the ways in
which the desert eagle population differed from other bald
eagle populations were not “adaptations . . . that could be
significant to the conservation of the taxon as a whole.” Id.

    FWS described a number of unusual characteristics of the
desert eagle population segment. First, birds in the desert
eagle population segment are smaller than, and breed earlier
than, other bald eagles. Id. at 25806–07. FWS concluded
that these variations correlated to latitude rather than to the
desert environment. Id. For example, Florida bald eagles,
who live further south than desert eagles, are even smaller,
and Baja California bald eagles, who also live further south,
breed even earlier. Id. at 25807. Second, a study found that
the desert eagle population’s eggs are less porous than those
of California bald eagles. However, the small sample size
(four eggs) and lack of analysis in the study meant that any
conclusion was not “scientifically robust.” Id. Third, the
12       CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

desert eagle population segment has a “preference for cliff
nests” that was unusual among other bald eagle populations.
Id. at 25808. FWS concluded that the preference was
explained by the availability of nesting sites in the desert and
by the “flexibility in nest site selection that bald eagles have
throughout [their] entire geographic range.” Id. Finally,
differences in migration patterns in young desert eagles were
consistent with the “wide variety of migration strategies
throughout the range of the species.” Id. We have no basis
to set aside these factual and scientific conclusions of FWS.

    Nor do we have any basis for holding, as a matter of law,
that if one of the four significance factors is satisfied, FWS is
compelled to conclude that a discrete population segment is
significant. While binding on the agency, Nw. Ecosystem
Alliance, 475 F.3d at 1138, the DPS Policy is open-ended. It
specifically provides that the agency’s “consideration may
include, but is not limited to” the four listed factors. 61 Fed.
Reg. at 4725. It provides, further, “Because precise
circumstances are likely to vary considerably from case to
case, it is not possible to describe prospectively all the classes
of information that might bear on the biological and
ecological importance of a discrete population segment.” Id.
The policy nowhere provides that if one of the listed factors
in the policy is satisfied, the agency is compelled to conclude
that the discrete population segment at issue is significant.

    CBD contends that FWS has always found significance
when it has found one of the four factors satisfied. FWS
disputes that this is so. But even assuming arguendo that the
FWS has always found significance after a finding that one of
the four factors is satisfied, this would show only that each of
the four factors is a powerful indicator of significance. A
close look at the persistence finding in this case illustrates the
         CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE              13

weakness of CBD’s argument. As summarized above, FWS
analyzed all of the unusual characteristics of the desert eagle
population segment. Though many of its characteristics are
indeed unusual, each characteristic (except the variation in
egg porosity, whose importance has not been established) can
be found in other bald eagle populations. FWS thus
reasonably concluded that, while the combination of unusual
characteristics in a discrete population was sufficient to
satisfy the persistence factor, those characteristics did not by
themselves necessarily require a conclusion that the desert
eagle population segment was ecologically or biologically
significant for the bald eagle taxon as a whole.

    B. Loss of Discrete Population Segment Resulting
       in Significant Gap in the Range of the Taxon

    FWS concluded that if the discrete population segment of
desert eagles were “extirpated,” this would not result in a
significant gap in the range of the bald eagle taxon. 77 Fed.
Reg. at 25809. CBD argues that FWS’s 2012 analysis is
flawed. It cites a 2009 draft prepared by FWS staff members
concluding, contrary to the conclusion reached by the FWS
in 2012, that the loss of the desert eagle population would
create a significant gap. The draft discussed the importance
of the desert eagle population segment as a “peripheral
population.” The 2012 FWS analysis does not use the term
“peripheral population.”

    The existence of the 2009 draft, which came to a contrary
conclusion about the significance of the gap that would be
created, is not irrelevant; but neither is it determinative.
Agencies may change course. Nat’l Ass’n. of Home Builders
v. Defenders of Wildlife, 551 U.S. 644, 659 (2007) (observing
that “the fact that a preliminary determination by a local
14      CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

agency representative is later overruled at a higher level
within the agency does not render the decisionmaking process
arbitrary and capricious.”). Our task is to review the change
of course to ensure that it is based on new evidence or
otherwise based on reasoned analysis. See Defenders of
Wildlife v. Zinke, 856 F.3d 1248, 1262 (9th Cir. 2017)
(“However, an agency also ‘must examine the relevant data
and articulate a satisfactory explanation for its action
including a rational connection between the facts found and
the choice made.’”) (quoting Humane Soc’y of U.S. v. Locke,
626 F.3d 1040, 1051 (9th Cir. 2010)). In so doing, “we must
defer to the agency’s interpretation of complex scientific
data.” Nw. Ecosystem Alliance, 475 F.3d at 1150 (citing
United States v. Alpine Land & Reservoir Co., 887 F.2d 207,
213 (9th Cir. 1989) (“Deference to an agency’s technical
expertise and experience is particularly warranted with
respect to questions involving engineering and scientific
matters.”)).

     We hold that FWS reasonably concluded that if the desert
eagle population segment were “extirpated,” this would not
create a significant gap in the range of the taxon. “For
purposes of the ‘gap in the range’ analysis, the term
‘significant’ has its ‘commonly understood meaning,’ which
is ‘important.’” Nw. Ecosystem Alliance, 475 F.3d at 1146
(quoting Nat’l Ass’n of Home Builders, 340 F.3d at 846). The
DPS Policy does not, however, define what constitutes a
“gap.” See 61 Fed. Reg. at 4725. Since the definition of gap
is ambiguous, the FWS is entitled to deference in interpreting
its own regulations, unless its interpretation is plainly
erroneous. Stinson v. United States, 508 U.S. 36, 45 (1993).

    In some prior cases, FWS has interpreted “gap” to include
the loss of peripheral populations. See Determination of
         CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE               15

Endangered Status for the So. Calif. Distinct Vertebrate
Population Segment of the Mountain Yellow-Legged Frog,
67 Fed. Reg. 44382, 44385 (July 2, 2002) (finding that “the
loss of the southern California frogs on the periphery of the
species’ range” would create a gap in the range of the taxon);
Final Rule to List the Santa Barbara County Distinct
Population of the Calif. Tiger Salamander as Endangered,
65 Fed. Reg. 57242, 57244 (Sep. 21, 2000) (finding that the
loss of the “southernmost population of the species” would
create a gap in the range of the taxon); Determination of
Threatened Status for the Northern Population of the
Copperbelly Water Snake, 62 Fed. Reg. 4183, 4184 (Jan. 29,
1997) (concluding that “[t]he loss of the peripheral, isolated,
northern population . . . would result in a significant reduction
in the range of the taxon.”).

     Peripheral populations are important to “significant gap”
analysis because, “[a]s a general matter, peripheral
populations often face ecological circumstances not found
elsewhere in the taxon’s range, and may consequently
develop distinctive morphological, behavioral, or genetic
characteristics through adaptation to local conditions.” Nw.
Ecosystem Alliance, 475 F.3d at 1146. Peripheral populations
thus help to create and preserve genetic variations in the
taxon. Nat’l Ass’n of Home Builders, 340 F.3d at 846. Such
genetic variations can help ensure the survival of the species
in times of stress when other parts of the taxon are vulnerable
to new and threatening conditions. The absence or
disappearance of a peripheral population can thus constitute
a “significant gap,” which in turn may require that the
peripheral population be protected as a DPS.

    In its 2012 decision, FWS emphasized the small size of
the desert eagle population segment. In 2009, in the Arizona
16       CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE

portion of the Sonoran Desert Area, where most of the desert
eagle population lives, there were only 48 breeding pairs.
77 Fed. Reg. at 25809. Counting the bald eagle taxon as a
whole, including in Alaska and Canada, the desert eagle
population segment “represents much less than one half of a
percent of the number of breeding pairs throughout the range
of the species.” Id. FWS determined that loss of the desert
eagle population would create a gap in the taxon’s range, and
that it is “unknown” whether bald eagles would repopulate
the Sonoran Desert Area if the desert eagle population were
“extirpated.” Id. But FWS concluded that there is “no
evidence of distinctive traits or genetic variations among the
Sonoran Desert Area population that suggests that loss of the
population would have a negative effect on the bald eagle as
a whole.” Id. In so concluding, FWS did not use the term
“peripheral population,” but the substance of its analysis
necessarily takes into account the benefits a peripheral
population, with its genetic variations, would confer on the
taxon as a whole.

                     C. Climate Change

    CBD’s final argument is that “FWS ignored climate
change as a factor in assessing whether desert eagles are
significant to their taxon.” This is not true. FWS directly
addressed climate change in its 2012 decision. It concluded,
“We are uncertain about the magnitude of the threat posed by
climate change . . . However, based on the best information
available, we conclude that climate change is not a significant
threat” to the bald eagle. Id. at 25826. The bald eagle is
“highly adaptable.” Id. “This . . . contributes to the ability of
the Sonoran Desert Area population of the bald eagle to
continue to exist even under some of the possible effects from
climate change.” Id. FWS then concluded that, given that the
        CTR. FOR BIOLOGICAL DIVERSITY V. ZINKE             17

desert eagle does not exhibit noticeable genetic variance from
the taxon as a whole, it is reasonable to assume that its
inherent characteristics exist in the species as a whole.

                         Conclusion

   For the foregoing reasons, the district court’s summary
judgment order is AFFIRMED.
