 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued September 23, 2016              Decided March 3, 2017

                         No. 14-5300

              DEFENDERS OF WILDLIFE, ET AL.,
                      APPELLEES

                              v.

  RYAN ZINKE, IN HIS OFFICIAL CAPACITY AS SECRETARY OF
 THE UNITED STATES DEPARTMENT OF THE INTERIOR, ET AL.,
                       APPELLANTS

                 STATE OF WYOMING, ET AL.,
                        APPELLEES


   Consolidated with 14-5311, 14-5312, 14-5313, 14-5314,
                          14-5315


        Appeals from the United States District Court
                for the District of Columbia
                    (No. 1:12-cv-01833)


     Joan M. Pepin, Attorney, U.S. Department of Justice,
argued the cause for Federal Appellants. With her on the briefs
were John C. Cruden, Assistant Attorney General, and David C.
Shilton, Attorney.
                               2

    Jay Jerde, Special Assistant Attorney General, Office of the
Attorney General for the State of Wyoming, argued the cause
for appellant State of Wyoming. Jeremiah I. Williamson,
Assistant Attorney General, entered an appearance.

   John A. Sheehan was on the brief for amicus curiae
Wyoming Wolf Coalition-2013's in support of appellant State of
Wyoming.

    Timothy J. Preso argued the cause for appellees/cross-
appellants Defenders of Wildlife, et al. With him on the brief
was Ralph E. Henry, Jr.

    Anna M. Seidman, Douglas S. Burdin, Jeremy S. Clare,
Michael T. Jean, and John I. Kittel were on the briefs for the
non-governmental defendant-intervenor-appellants/cross-
appellees. Christopher A. Conte entered an appearance.

    Before: ROGERS, BROWN and PILLARD, Circuit Judges.

    Opinion for the Court filed by Circuit Judge ROGERS.

     ROGERS, Circuit Judge: The gray wolf in Wyoming has
been a protected species since 1973 pursuant to the Endangered
Species Act (“ESA”) and its predecessor. In 2011, the Secretary
of the Interior proposed to delist the wolf on the basis of the
recovery of the Northern Rocky Mountain gray wolf population
and the conservation management plan of the State of Wyoming.
Environmental groups opposed the delisting, and thereafter
Wyoming made statutory and regulatory changes and created an
Addendum to its management plan. Upon consideration of these
changes and other data, the Fish and Wildlife Service, acting on
the Secretary’s behalf, delisted the wolf in Wyoming as it had in
the adjacent states of Montana and Idaho. Removal of the Gray
Wolf in Wyoming From the Federal List of Endangered and
                                3

Threatened Wildlife and Removal of the Wyoming Wolf
Population’s Status as an Experimental Population, 77 Fed.
Reg. 55,530 (Sept. 10, 2012) (the “Rule”). Environmental
groups sued, and the district court vacated the Rule, agreeing
that the Service had arbitrarily determined that Wyoming had
put into place adequate “regulatory mechanisms.” 16 U.S.C.
§ 1533(a)(1)(D). The court rejected the environmental groups’
other challenges to the Rule.

     The Secretary and the State of Wyoming appeal, principally
on the ground that the district court erred by failing to defer to
the Service’s reasonable interpretation of “regulatory
mechanisms” to include the State’s management plan for a wolf
population buffer, which although not itself legally binding, is
a practical entailment of the State’s statutory population minima.
Environmental groups cross-appeal the district court’s
conclusions that the Rule includes adequate provisions on
genetic connectivity between wolf subpopulations and does not
imperil the wolves in a “significant portion” of their range. For
the following reasons, we reverse the judgment vacating the
Rule and otherwise affirm.

                                I.

    Section 4(a)(1) of the ESA provides that the Secretary is to
determine whether a species is endangered or threatened because
of one or more 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.
                                  4

16 U.S.C. § 1533(a)(1). This determination is to be made
“solely on the basis of the best scientific and commercial data
available . . . after taking into account those efforts, if any, being
made by any State . . . to protect such species, whether by
predator control, protection of habitat and food supply, or other
conservation practices, within any area under its jurisdiction.”
Id. § 1533(b)(1)(A). A species — defined to include “any
distinct population segment . . . which interbreeds when
mature,” id. § 1532(16) — must be listed if its survival is
threatened or endangered “throughout all or a significant portion
of its range,” id. § 1532(6), (20). Section 4(f) requires the
Secretary to develop and implement recovery plans for all listed
species, id. § 1533(f)(1), incorporating “objective, measurable
criteria which, when met, would result in a determination . . .
that the species be removed from the list,” id.
§ 1533(f)(1)(B)(ii). Once the species has recovered sufficiently
to be delisted, Section 4(g) requires the Secretary, in cooperation
with the States, to monitor the species’ status “for not less than
five years.” Id. § 1533(g)(1). Additionally, the Secretary is
instructed to “make prompt use of the authority . . . to prevent a
significant risk to the well being of any such recovered species.”
Id. § 1533(g)(2). By regulation, the Secretary has instructed that
upon listing a species the Fish and Wildlife Service (hereinafter,
“the Service”) shall develop and implement recovery plans
calling for “improvement in the status of listed species to the
point at which listing is no longer appropriate under the criteria
set out in section 4(a)(1) of the [ESA].” 50 C.F.R. § 402.02.

     The Northern Rocky Mountain gray wolf had by the 1930s
been extirpated from Montana, Idaho, and Wyoming by western
settlers who aggressively poisoned, trapped, and shot them. In
the 1980s, gray wolves from Canada began to colonize
northwestern Montana. In 1995 and 1996, 35 wolves from
Alberta and British Columbia were reintroduced in Central
Idaho, and 31 more were reintroduced in Yellowstone National
                                5

Park, virtually all of which is in northwestern Wyoming. The
Service set recovery goals for Montana, Idaho, and Wyoming
of at least 10 breeding pairs and 100 wolves, for a total Northern
Rocky Mountain population of at least 30 breeding pairs and
300 wolves, with adequate genetic connectivity between the
three subpopulations (i.e., at least one migrant per generation
that disperses from one subpopulation to another and
successfully breeds). 76 Fed. Reg. 61,782, 61,791, 61,814 (Oct.
5, 2011) (“NPRM”).

     The Service designated the Northern Rocky Mountain gray
wolf as a distinct population segment in 2008, and proposed in
2009 to delist the wolf in Montana and Idaho. Following
various court challenges and intervention by Congress, that
delisting occurred in 2011. Reissuance of Final Rule to Identify
the Northern Rocky Mountain Population of Gray Wolf as a
Distinct Population Segment and to Revise the List of
Endangered and Threatened Wildlife, 76 Fed. Reg. 25,590 (May
5, 2011); see also All. for the Wild Rockies v. Salazar, 672 F.3d
1170, 1171–72 (9th Cir. 2012). In proposing delisting in
Wyoming in 2011, the Service recounted the characteristics and
history of the gray wolf. NPRM, 76 Fed. Reg. at 61,788–89.
These characteristics include adaptability, resiliency,
territoriality, an ability to reproduce quickly, and a tendency to
live in family packs of two to twelve, although sometimes
significantly larger. From 1995 to 2008, the Northern Rocky
Mountain gray wolf population grew an average of 20%
annually despite an average human-caused mortality rate of
23%. By 2002, the recovery goal had been met for three
consecutive years. At the end of 2011, the Northern Rocky
Mountain gray wolf population consisted of a minimum of 1,774
wolves and 109 breeding pairs, thus far exceeding the Service’s
recovery goals. Rule, 77 Fed. Reg. at 55,539. This population
represented a 400-mile “southern range extension of a vast
contiguous wolf population that number[ed] over 12,000 wolves
                                6

in western Canada and about 65,000 wolves across all of Canada
and Alaska.” Id. at 55,547.

     The Service’s proposal to delist the remaining Northern
Rocky Mountain gray wolves in Wyoming was based on
federal-state cooperative efforts to develop an adequate state
regulatory framework, taking into account court decisions that
had found prior state plans deficient. First, because a significant
part of the Wyoming gray wolf subpopulation lives beyond
Wyoming’s jurisdiction on tribal and federal lands — the Wind
River Indian Reservation and Yellowstone National Park — the
Service concluded that it would suffice for Wyoming to
maintain a wolf population of “at least” 10 breeding pairs and
100 wolves in the parts of the State over which Wyoming has
jurisdiction. NPRM, 76 Fed. Reg. at 61,788. The wolves on
tribal and federal lands, in turn, would provide an “additional
buffer” above minimum recovery goals, id., thus roughly
aligning Wyoming with the existing management requirements
of 15/150 in Montana and Idaho, id. at 61,791. To meet these
obligations, Wyoming agreed to repeal a regulatory requirement
that it aggressively manage the wolf population down to the bare
minimum required by law. In addition, it stated in its
management plan that it intended “to maintain an adequate
buffer above the minimum recovery goals” to ensure that
unexpected mortality did not jeopardize its compliance with the
10/100 minima. Id. at 61,788. Next, Wyoming would manage
wolves as game animals in a permanent trophy area that
comprises 15.2% of the State, in which the vast majority of
Wyoming wolves live. During the peak dispersal season, the
trophy area would also expand southward approximately 1,300
square miles and cover an additional 1.3% of the State, to
protect wolves migrating to and from the Idaho subpopulation.
The remaining area, which covers only 19% of the State’s
suitable wolf habitat, would be designated a predator area in
which wolves could be killed with few restrictions.
                                 7


     Taking these commitments together, the Service concluded
that Wyoming had provided for adequate regulatory
mechanisms and proposed delisting contingent upon Wyoming
enacting the agreed-upon changes into law. Id. at 61,811.
Wyoming did so. See, e.g., Wyo. Stat. Ann. § 23-1-
101(a)(xii)(B)(I), (II); id. § 23-1-304(a), (n). Consistent with the
Service’s practice of submitting its rulemakings for independent
peer review, four of five peer reviewers agreed that, under the
proposed regulatory framework, Wyoming’s wolf population
would continue to be viable after delisting. Rule, 77 Fed. Reg.
at 55,538. Some commenters disputed the adequacy of
Wyoming’s management plan and, in particular, the danger that
human-caused mortality could reduce the wolf population below
Wyoming’s required minimum. See id. at 55,555. In response,
Wyoming submitted an Addendum to its management plan to
affirm its commitment to maintain an adequate population
buffer above minimum recovery levels, to “be determined
through an adaptive management approach and [which] may
fluctuate based on natural population dynamics and the effects
of specific management actions.” Wyo. Game & Fish Comm’n,
Addendum: Wyoming Gray Wolf Management Plan at 3–5
(Mar. 22, 2012) (the “Addendum”). The Service relied on this
Addendum in promulgating the Rule, stating, for instance, that
“Wyoming’s wolf population will be further buffered because
[the State Commission] intends to maintain an adequate buffer
above minimum population objectives.” 77 Fed. Reg. at 55,538;
id. at 55,555–56.

    The district court, in response to two lawsuits challenging
the Rule, granted the environmental groups’ motion for
summary judgment in part. It upheld Wyoming’s management
plan as adequate to ensure genetic connectivity between the
three gray wolf subpopulations. It also upheld the Service’s
determination that the predator area in southern and eastern
                                8

Wyoming does not constitute a “significant portion” of the gray
wolf’s range, and that a lack of protection in those areas will not
prevent genetic exchange. It concluded, however, that
Wyoming’s inadequate regulatory framework rendered arbitrary
the Service’s determination that the wolf is not threatened or
endangered in Wyoming. The district court found that, although
the Rule imposed on Wyoming a duty to manage above the
minimum level of 10 breeding pairs and 100 wolves, and
although Wyoming statutes had been amended to require “at
least” the minimums, only the Addendum to the State’s
management plan included a commitment to managing above
that level and it was not legally enforceable. Absent that legal
commitment to maintain the buffer, the district court vacated the
Rule. See Defs. of Wildlife v. Jewell, 68 F. Supp. 3d 193,
209–10 (D.D.C. 2014).

     The Secretary, Wyoming, Safari Club, and the National
Rifle Association appeal the vacatur of the Rule, and the
environmental groups (hereinafter, “appellees”) cross-appeal the
denial of summary judgment on their genetic connectivity and
“significant portion” challenges to the Rule. Our review of the
grant or denial of summary judgment is de novo. See Defs. of
Wildlife v. Jewell, 815 F.3d. 1, 7 (D.C. Cir. 2016). Where, as
here, the district court reviewed agency action under the
Administrative Procedure Act (“APA”), our review is highly
deferential to the agency, see American Wildlands v.
Kempthorne, 530 F.3d 991, 997–98 (D.C. Cir. 2008), while
according no particular deference to the judgment of the district
court, see In re Polar Bear Endangered Species Act Listing, 709
F.3d 1, 8 (D.C. Cir. 2013); accord Friends of Blackwater v.
Salazar, 691 F.3d 428, 432 (D.C. Cir. 2012).
                                9

                               II.

      Under Section 4(a) of the ESA, one of the statutory factors
that the Secretary must consider in determining whether to delist
a protected species is “the inadequacy of existing regulatory
mechanisms.” 16 U.S.C. § 1533(a)(1)(D). Section 4(b), in turn,
requires the Secretary to consider a broad range of conservation
efforts, if any, being made by the state to protect the species.
See id. § 1533(b)(1)(A). The Secretary contends that nothing in
the ESA requires those efforts to be legally binding.

     Tracking the familiar two-step analysis under Chevron
U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467
U.S. 837, 842–43 (1984), the Secretary points out that the plain
language of “regulatory mechanisms” is broader than only
legally binding measures. Had Congress intended to so limit the
analysis, it could have used “State law or regulation,” as it did
elsewhere in the ESA, e.g., 16 U.S.C. § 1535(f). Moreover, a
requirement that Section 4(b) efforts be legally binding would
be duplicative of Section 4(a)(1)(D), which addresses existing
“regulatory mechanisms.” Id. § 1533(a)(1)(D). Therefore, the
Secretary concluded the term “regulatory mechanisms” was
ambiguous and may permissibly include state management plans
that do not have the force of law. We agree that Congress has
not “directly spoken” to the question, Chevron, 467 U.S. at 842,
and that the term is ambiguous, see id. at 843, for the reasons the
Secretary explains. Further, under Chevron’s second step, it was
“permissible,” id., for the Secretary to rely on Wyoming’s
management plan, which includes a commitment to manage for
a buffer in conjunction with its statutory obligations. The
Secretary properly does not view the management plan as
merely a speculative promise of future action in light of
Wyoming’s statutory and regulatory amendments. Although
appellees rely on the dictionary in maintaining that a
“‘regulation’ demands more than voluntary compliance,” see
                                10

Appellees Br. 32 (citing 13 OXFORD ENGLISH DICTIONARY 524
(2d ed. 1989)), they overlook that Wyoming “is implicitly
‘required’ [to maintain a buffer] as the only practicable means
of achieving the explicit requirement of maintaining at least” 10
breeding pairs and 100 wolves on state land. Fed. Appellants
Reply Br. 13 (first emphasis added); Wyo. Stat. Ann. § 23-1-
304(a).

     Much of the parties’ underlying legal dispute about the
adequacy of Wyoming’s management plan has been addressed
by this court. In In re Polar Bear, 709 F.3d 1, this court
discussed “regulatory mechanisms” and “conservation efforts”
interchangeably, concluding that the Service reasonably found
that existing regulatory mechanisms were inadequate despite
Canada’s use of sport-hunting fees to fund local conservation
programs, which it determined did nothing to offset the threat to
polar bears from loss of sea ice habitat. Id. at 16–17. More
significantly, and post-dating the district court’s vacatur of the
Rule, this court upheld the Service’s determination to rely on a
state management plan in Defenders of Wildlife, 815 F.3d at 6,
17, crucial terms of which were conservation agreements
voluntarily entered into by landowners seeking to earn
environmental mitigation credits that would relieve them of
additional duties if the species at issue were listed. As here, the
exercise of judgment by the Service in that case was based upon
its experience under similar management plans in two adjacent
states, with species-protective terms that, although not
themselves legally codified, the Service had seen in operation
and was reasonably certain would be fulfilled. Id. at 6–7. There
too, environmental objections were raised similar to those of
appellees, but the court concluded the Service adequately
responded to them and exercised its judgment in a responsible
and reasoned way. Id. at 17.

    In other words, the question now before the court turns on
                                11

whether the rulemaking record demonstrates the Service
exercised its judgment in a reasonable way in concluding that
Wyoming’s management plan, which explains how the State
intends to carry out its day-to-day implementation of its legal
obligations, will adequately protect Wyoming’s gray wolf
population after delisting. See 16 U.S.C. § 1533(a)(1)(D),
(b)(1)(A). That determination, this court acknowledged, is a
quintessential judgment call that Congress left to the Secretary,
and by delegation to the Service, which has years of experience
in evaluating what is reasonably likely to be implemented and
effective. See Defs. of Wildlife, 815 F.3d at 17. The ESA
provides no definition of “regulatory mechanisms,” and neither
the district court nor appellees suggests why the Secretary’s
interpretation is unreasonable. Although appellees may disagree
with the Service’s conclusion that Wyoming can be trusted to
manage for a buffer, that is a separate question. Given
Congress’s direction that state conservation efforts must be
considered, 16 U.S.C. § 1533(b)(1)(A), their consideration as
part of the State’s “regulatory mechanisms” is hardly contrary
to congressional intent. Appellees disagree with the Service’s
assessment of Wyoming’s management plan, but not with the
statutory obligation to take into account all state conservation
efforts, or with the proposition that, in some instances, non-
binding measures “if sufficiently certain and effective to
alleviate a threat [of endangerment] may render a [legally
binding] regulatory mechanism unnecessary . . . after delisting,”
Appellees Br. 37-38. The Rule may be set aside only if
“arbitrary, capricious, an abuse of discretion, or otherwise not in
accordance with law.” Am. Wildlands, 530 F.3d at 997 (quoting
5 U.S.C. § 706(2)); see Motor Vehicle Mfrs. Ass’n of U.S., Inc.
v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 42–43 (1983).

    The record demonstrates that the Service reasonably and
adequately responded to concerns about the reliability of
Wyoming’s management plan. As the preamble to the Rule
                                12

makes clear, the Service determined that Wyoming’s
management plan is a reliable indicator of how the State plans
to implement its statutes and regulations because that plan
aligned with the State’s own incentives. That is, managing at
minimum levels “would severely limit State flexibility to
address wolf depredation issues, limit wolf harvest
opportunities, and increase the risk of relisting.” Rule, 77 Fed
Reg. at 55,567. The Service similarly noted that a failure to
ensure a buffer would place Wyoming at risk of violating its
own statutory and regulatory commitments, if faced with
unexpected and uncontrollable sources of mortality like disease.
Id. As a point of comparison, the Service also looked to the
post-delisting behavior of the adjacent states of Montana and
Idaho, which had both maintained wolf populations well above
minimum targets. See id. at 55,567–68. It noted that none of
the states had indicated any interest in managing down to
minimum levels; the Service underscored that state wildlife
managers “have consistently reiterated . . . their desire not to
come close to their floor levels” due to concerns about reduced
management flexibility and potential relisting. Id. at 55,567.

     The district court did not question those assumptions or
considerations, but vacated the Rule solely because the
provision in Wyoming’s management plan for an additional
buffer is not legally binding. Nothing in the ESA demands that
level of certainty, however, and in Defenders of Wildlife, the
court upheld the withdrawal of a listing proposal where the
Service had found that the voluntary conservation efforts were
“sufficiently certain to be implemented” based on the strength
of the participating state’s incentives, 815 F.3d at 6 (quoting the
Service’s Policy for Evaluation of Conservation Efforts When
Making Listing Decisions, 68 Fed. Reg. 15,100, 15,114–15
(Mar. 28, 2003)). The Service’s decision to delist in the absence
of legal certainty is compatible with the ESA’s requirement for
monitoring of the species after delisting “for at least five years”
                                13

and its emergency provisions authorizing the Secretary to take
immediate action to ensure the delisted species does not become
threatened or endangered again. See 16 U.S.C. § 1533(b)(7),
(g). So understood, the Service could reasonably conclude that
Wyoming’s efforts set forth in its management plan were
sufficiently certain to be implemented based on the strength of
the State’s incentives. And although Wyoming’s antagonistic
history toward wolves may provide appellees reason to disagree,
the Service took that history into account, see, e.g., Rule, 77
Fed. Reg. at 55,566, and it worked with the State to rectify
deficiencies previously identified by the courts, id. at 55,551–52.
That appellees disagree with the Service does not undercut its
reasoned determination that, in light of Wyoming’s plan to
manage for a buffer, especially given the State’s own interests,
Wyoming has established an adequate regulatory framework.

     Appellees nonetheless maintain the Service’s reliance on a
non-binding management plan is arbitrary because the Service
had already determined that the threat of human mortality must
be “adequately regulated.” Appellees Br. 38–39 (quoting Rule,
77 Fed. Reg. at 55,588). The preamble to the Rule does not state
that Wyoming’s buffer must be regulated; to the contrary, it was
the general threat of human-caused mortality that required
regulation “in the form of binding minimum population targets
by geographic area.” 77 Fed. Reg. at 55,568. The Service found
that such protections are in place. Wyoming is bound under its
own law to manage for “at least ten (10) breeding pairs of gray
wolves and a total of at least one hundred (100) individual gray
wolves.” Wyo. Stat. Ann. § 23-1-304(a). It will also use a
licensing system to regulate the frequency with which wolves
can be killed in the trophy area, see, e.g., Wyo. Admin. Code
Game Hunt Ch. 21 § 7, which affords Wyoming additional
control over human-caused mortality. See Greater Yellowstone
Coal., Inc. v. Servheen, 665 F.3d 1015, 1032 n.7 (9th Cir. 2011).
Elsewhere, the preamble is even clearer on this point, discussing
                                14

regulation and buffers separately: “[I]f human-caused mortality
is adequately regulated and population targets are sufficient to
allow for other potential unforeseen or uncontrollable sources of
mortality, no other potential threats are likely to compromise the
population’s viability.” Rule, 77 Fed. Reg. at 55,588. Because
the Service never deemed a regulatory buffer necessary, it did
not contradict itself by failing to require one.

    Nor did the Service disclaim any reliance on the states’
incentives to manage for a buffer, as appellees suggest. The
preamble to the Rule states:

         Should management needs be identified in future years,
         all three States have regulatory authority to modify
         management to meet such needs; although we did not
         rely upon this in making our decision, we recognized
         all three States have a strong incentive to maintain the
         [Northern Rocky Mountain distinct population
         segment] and its subpopulations well above minimum
         population levels.

77 Fed. Reg. at 55,590 (emphasis added). Appellees read “this”
to refer to the states’ “strong incentive” in the following clause,
while the Secretary responds that it refers to the states’
“regulatory authority” in the preceding clause. Even assuming
the sentence is not a model of clarity, its meaning is apparent
upon examination. If “this” were meant to refer to “strong
incentive” in the following clause, then there would be no
conceptual link between the two halves of the sentence, and they
would have been separated by a period rather than a semi-colon.
The sentence, moreover, comes at the end of a section
explaining the adequacy of Wyoming’s current regulatory
structure, and cannot fairly be understood as meaning “And even
if the current regulatory structure is inadequate, Wyoming can
just change it.” Instead, the Service noted Wyoming’s authority
                                 15

to legislate while making clear that it did not rely on this fact; it
relied on the State’s incentives to make sure future legislation is
unnecessary. The preamble, further, makes clear that the
Service did rely on state incentives, see, e.g., Rule, 77 Fed. Reg.
at 55,567, so it would have been illogical for it to claim
otherwise.

     Also without merit is Wyoming’s position that it is not
required to manage for a buffer at all. This sleight of hand may
lend some credence to appellees’ concerns about the State’s
commitment, but it cannot overcome the rulemaking record and
the documents submitted by the State in order to obtain
delisting. The Service considered “unacceptable” Wyoming’s
previous approach of managing down to bare minimum levels.
Rule, 77 Fed. Reg. at 55,588. More to the point, the preamble
states that Wyoming “will, and must, maintain a buffer to
consistently meet its minimum management targets.” Id. at
55,556 (emphasis added). This language manifests a clear intent
by the Service to bind Wyoming, and therefore the preamble
itself has the force of law. See Kennecott Utah Copper Corp. v.
U.S. Dep’t of Interior, 88 F.3d 1191, 1223 (D.C. Cir. 1996).
Wyoming’s Addendum acknowledges that managing for
minimum populations would restrict its ability to deal with
depredating wolves and risk a status review and potential
relisting. See Rule, 77 Fed. Reg. at 55,567; 16 U.S.C.
§ 1533(b)(7), (g). As the Secretary explains, Wyoming is
implicitly required to maintain a buffer “as the only practicable
means of achieving the explicit requirement” of maintaining at
least 10 breeding pairs and 100 wolves on state land. Fed.
Appellants Reply Br. 13; Wyo. Stat. Ann. § 23-1-304(a).

     Appellees’ remaining challenges to Wyoming’s regulatory
framework, which the district court did not reach in light of its
vacatur of the Rule, also lack merit. First, the Service was not
arbitrary in relying on Wyoming’s management plan to maintain
                               16

the statutorily required buffer, contrary to appellees’ contention
that maintaining a buffer would conflict with state law.
Appellees point to Wyoming’s lethal take statute but ignore the
statutory and regulatory limitations that preserve the State’s
buffer authority. The statute provides for the promulgation of
rules under which permits “shall be issued as long as the
removals authorized by such permits could not reduce the
numbers of gray wolves below” the 10/100 minimum. Wyo.
Stat. Ann. § 23-1-304(n). The rules “shall provide for
suspending the issuance of permits or cancelling existing
permits if further lethal control could cause the numbers of gray
wolves to be reduced below” the minimum. Id. As
promulgated, those rules provide that a “Lethal Take Permit
shall only be issued by the Department if legal removal of gray
wolves will not prevent the Department from” meeting the
10/100 minimum. Wyo. Admin. Code Game Hunt Ch. 21 §
7(a). If further lethal take “may prevent the Department from
achieving [its] management objectives,” the issuance of
additional permits “shall be immediately suspended” and
existing permits “shall be immediately cancelled.” Id.
§ 7(b)(iii). In addition to these binding provisions, the
Addendum states that “[i]f the population approaches the
minimum recovery level . . . the Department has the statutory
authority to suspend issuance of Lethal Take Permits or cancel
existing Lethal Take Permits.” Addendum at 7.

     The Service concluded that these provisions will not
interfere with Wyoming’s ability to maintain a buffer because
they require the suspension or cancellation of permits if further
mortality “could” compromise the State’s minimums. Rule, 77
Fed. Reg. at 55,557. If State law had said “would” or “will,”
then it might conflict with a buffer, but State law requires
suspension of permits upon the possibility of compromise. See
id. Appellees focus on the phrase “permits shall be issued,”
maintaining this mandatory language trumps any discretion the
                                17

State might otherwise have to provide for a buffer. They ignore
that the mandate (“shall”) is tempered by a condition (“as long
as [issuance] could not reduce” the population below 10/100).
Wyo. Stat. Ann. § 23-1-304(n) (emphasis added). In other
words, the mere possibility that minimums “could” be
compromised is enough to warrant the permit’s rejection. See
77 Fed. Reg. at 55,557. To the extent appellees also maintain
that, because the preamble’s reference to “could” is not present
in the State regulation, a permit must be issued as long as it “will
not prevent” Wyoming from reaching its minimum, Appellees
Br. 47–48 (quoting Wyo. Admin. Code Game Hunt Ch. 21
§ 7(a)), they overlook that the permit “shall only be issued . . .
if [it] will not prevent” Wyoming from reaching its minimum.
Wyo. Admin. Code Game Hunt Ch. 21 § 7(a). The regulation
sets a necessary condition, not a mandate, for the permit to be
issued. See also id. § 7(b) (“If the requirements of . . . Section
7(a) are met . . . .”). As noted, a separate provision requires the
suspension or cancellation of permits if they “may” prevent
Wyoming from managing for 10/100, see id. § 7(b)(iii), thus
preserving the State’s ability to maintain a buffer if the wolf
population falls to near minimum levels.

     Appellees also point out that Wyoming’s lethal take statute
authorizes a permit when wolves are “harassing . . . livestock or
other domesticated animals,” Wyo. Stat. Ann. § 23-1-304(n),
and yet it fails to define “harassing.” They worry that if the
State were to define “harassing” broadly, permitting under that
provision could jeopardize any planned buffer. In downplaying
this concern, the Service relied on a letter from Wyoming’s
Governor stating that prior to issuing a permit due to
harassment, State officials will verify that wolves were present
and that an actual attack was likely. Rule, 77 Fed. Reg. at
55,585–86 (citing Letter of Gov. Matthew H. Mead to U.S. Fish
& Wildlife Serv. (May 15, 2012)). Appellees maintain that the
Service’s reliance on the Governor’s letter was unreasonable,
                               18

because it is a non-binding promise, but that issue is largely
irrelevant. Regardless of how broadly Wyoming defines
“harassing,” or whether it independently verifies harassment
before issuing a permit, it is legally bound to suspend all
harassment permits if they “could” compromise the State’s
minimums. Wyo. Stat. Ann. § 23-1-304(n).

      Second, appellees maintain the Service’s delisting action
was arbitrary because it failed to secure a regulatory
commitment to suspend permits where necessary to ensure
genetic connectivity between subpopulations. They correctly
point out that the Service had identified this as a “Major Issue”
in a mark-up of Wyoming’s proposed regulations,
recommending that Wyoming add genetic connectivity as
another grounds for suspending permits. Appellees, however,
tell only half of the story. The Service also noted in the mark-up
that it “could live with a commitment to this goal generally here,
and let the [management] plan include more specifics.” Draft
Revisions, Chapter 21 Regulations – Gray Wolf Management,
at 4 (Feb. 24, 2012). Consistent with that guidance, the final
State regulation added a general commitment to “ensur[ing]
genetic diversity and connectivity,” even though it was not
included in Section 4(a)(i) as the Service’s reviewer would have
preferred. See Wyo. Admin. Code Game Hunt Ch. 21 § 4(a)(ii).

     To the extent appellees maintain the Service arbitrarily
ignored that Wyoming’s lethal take regulations could override
that non-binding commitment to genetic connectivity, the
Service correctly points out that the ESA “does not mandate that
regulatory mechanisms exist to protect a species from any
conceivable impact.” Fed. Appellants Reply Br. 31. Rather, the
ESA requires protection only “against threats that would cause
the species to be ‘an endangered species or a threatened
species.’” Id. (quoting 16 U.S.C. § 1533(a)(1)). Because the
rulemaking record showed that the wolves’ genetic health is
                                19

strong, and because Wyoming has other tools at its disposal
(including reduction in harvest levels and in its own wolf control
actions, and, if necessary, translocating wolves to other
subpopulations), the Service concluded that the State’s
commitment to ensuring genetic connectivity into the Greater
Yellowstone Area (“GYA”) was sufficient. Rule, 77 Fed. Reg
at 55,595–96. Even if a close issue, because the Service
considered this permitting exception important, the studies in the
record support the Service’s view that genetic connectivity is not
an immediately pressing concern. See Michael D. Jimenez et
al., Wolf Dispersal in the Northern Rocky Mountains in Western
United States: 1993 – 2008 (2011) (“Jimenez Study”); Bridgett
M. vonHoldt et al., A Novel Assessment of Population Structure
and Gene Flow in Grey Wolf Populations of the Northern Rocky
Mountains of the United States, 19 Molecular Ecology 2214
(2010) (“vonHoldt Study”). The Service determined that “even
if no new genes entered into the GYA (a near impossibility),
genetic diversity is likely many decades, and perhaps a century
or more, away from becoming an issue and even then, it would
be unlikely to threaten the GYA population.” Rule, 77 Fed.
Reg. at 55,596. In this context, the Service’s acceptance of a
non-binding commitment to genetic connectivity was not
arbitrary and capricious.

     Third, appellees maintain that any buffer will be
undermined by Wyoming’s allowance for unlimited killing of
wolves “doing damage to private property.” Wyo. Stat. Ann.
§ 23-3-115. Although the Service relied on the State’s ability to
limit human-caused mortality, e.g., Rule, 77 Fed. Reg. at 55,555,
appellees view this provision to create a “hole . . . in the State’s
authority.” Appellees Br. 54. In particular, appellees are
concerned about the ability of ranchers to bait wolves onto their
property by leaving animal carcasses out. The Service
concluded this concern was “improbable [and] theoretical,”
noting that a representative of the Wyoming Attorney General’s
                               20

office advised that baiting could be prosecuted under Wyoming
law. Rule, 77 Fed. Reg. at 55,561. In the Service’s judgment,
“such a scenario is unlikely to occur and exceedingly unlikely
to become a meaningful source of mortality” because ranchers
are more likely to seek a lethal take permit or hunting tag than
risk prosecution for baiting. Id. It noted as well that, baiting
aside, similar defense-of-property allowances have been in place
in Montana and Idaho since delisting and the overall wolf
population has continued to grow. Id. at 55,585. Indeed, the
record reflects that in Idaho only six defense-of-property kills
are known to have occurred in 2009 and thirteen in 2010. Thus,
the Service determined that the allowance “will not compromise
. . . Wyoming’s ability to meet the agreed-upon population
objectives.” Id. Appellees speculate that baiting could become
most problematic as population levels decrease to near 10/100,
at which point permits would be suspended and ranchers would
have no choice but to bait. Again, as the Secretary observes, the
ESA does not require a regulation to address every “far-fetched
‘what-if’ scenario” that opponents of delisting can imagine.
Fed. Appellants Reply Br. 35. Given the slight impact of these
allowances in Idaho and Montana, and the absence of evidence
of baiting, the Service was not unreasonable in rejecting this
concern.

                               III.

     On cross appeal, appellees contend that the Service
arbitrarily concluded that genetic connectivity is currently
sufficient, and will remain so after delisting. They also contend
the Service arbitrarily concluded Wyoming’s unregulated
predator area is not a “significant portion” of the wolves’ range.
We are not persuaded that the district court erred in rejecting
appellees’ challenges.
                               21

                               A.
     To ensure the wolves’ long-term genetic health, the Service
has determined that, as a general rule, there should be at least
one effective migrant per generation, i.e., one wolf that travels
every four years from another subpopulation and passes on its
genes. Rule, 77 Fed. Reg. at 55,593. The GYA is the most
isolated core recovery area within the Northern Rocky Mountain
region, and thus a key concern of the Service has been the
number of effective migrants entering the GYA from northwest
Montana and central Idaho.

     The Service relied on two studies to determine that genetic
connectivity is currently sufficient. The Jimenez Study found
that five radio-collared wolves had migrated into the GYA
between 1992 and 2008, of which two were confirmed to have
mated successfully and one was confirmed not to have. Rule, 77
Fed. Reg. at 55,593. Because only 20–30% of wolves were
radio-collared, the Service determined that the number of actual
migrants was likely several times higher than the five
documented. Applying the Jimenez Study’s estimate that 35%
of migrants effectively breed, the Service concluded that there
was likely more than one effective migrant per generation, and
specifically as many as 1.5. Because the number of dispersals
increase as the wolf population increases, and the Northern
Rocky Mountain population increased from 55 to more than
1,655 over the course of the study, the Service inferred that a
large proportion of dispersals occurred in recent years.

    The vonHoldt Study sampled genetic material of Northern
Rocky Mountain wolves between 1995 and 2004, when the total
population was between 101 and 846 wolves. Id. It “detected
genetically effective dispersal among the three recovery areas,”
with high levels of genetic variation and low levels of
inbreeding. vonHoldt Study at 4412. As the population
expanded over the course of the study, “observed heterozygosity
                               22

remained high,” id. at 4416, and “[i]nbreeding coefficients . . .
remained low for all recovery phases,” id. at 4417. A co-author
of the vonHoldt Study, Daniel Stahler, determined separately
that the genetic sampling data indicated a minimum of 0.42
effective migrants per generation had entered the GYA during
the study. There was consensus that this significantly
underestimated the number of actual effective migrants because
only about 30% of the population was sampled, but
disagreement about how to calculate the actual number. One
paper suggested that the Stahler estimate is “almost certainly
low by at least half,” Rule, 77 Fed. Reg. at 55,593 (quoting
Mark Hebblewhite et al., Restoration of Genetic Connectivity
Among Northern Rockies Wolf Populations, 19 Molecular
Ecology 4383, 4384 (2010) (“Hebblewhite et al., Genetic
Connectivity”)), but Stahler has objected to that particular
extrapolation as mere guesswork. The Rule’s preamble quoted
Hebblewhite’s multiplier as a “suggest[ion],” while noting that
additional analysis “may be needed” to pin down the actual
number. Id.

     Appellees contend that these studies show that the
minimum requirement of one effective migrant per generation
has not been met, and that the Service’s contrary conclusion was
arbitrary. They claim the Jimenez Study found “[o]nly two
dispersing wolves actually bred,” Appellees Br. 61, thus
resulting in approximately 0.62 effective migrants per
generation. Leaving aside that this Study accounted for only
20–30% of the wolf population, appellees ignore that two other
dispersing wolves may have effectively bred, as only one of the
five was confirmed not to have done so. Thus, it is possible that
the dispersals observed by the Jimenez Study alone met the
threshold, even before extrapolating the effective dispersals of
the entire population. Appellees similarly take issue with the
Service’s reliance on the vonHoldt Study because even
assuming Hebblewhite is correct that the 0.42 effective migrant
                                23

rate is too low by half, a 0.84 rate would still be insufficient.
They understand Stahler to believe that Hebblewhite
overestimated the actual effective migrant rate. In fact, Stahler
clarified that he was not claiming that the actual number could
not be “as high as this (or higher in recent years),” but simply
that no data supported quantifying the actual number as at least
double the observed number. Email from Dan Stahler to Mike
Jimenez and Seth Willey (Sept. 7, 2011). Contrary to appellees’
assertion, the Service did not “fail[] to grapple with Stahler’s
objection,” Appellees Reply Br. 10, but rather cited Stahler in
noting that additional analysis may be needed. Rule, 77 Fed.
Reg. at 55,593.

     The ESA requires that the Service rely on the “best
scientific . . . data available,” 16 U.S.C. § 1533(b)(1)(A), and the
Service’s evaluation of this data falls within its area of expertise
and is entitled to deference by the court. Defs. of Wildlife, 815
F.3d at 14. Appellees do not suggest that there are better studies
available, nor do they meaningfully dispute that both studies’
results are understated, requiring some extrapolation upward.
Instead, they disagree with the Service’s conclusion that the
studies show an effective migrant rate above one per generation.
Such competing views about scientific data and policy choices,
however, fail to show that the Service’s conclusions were
arbitrary and capricious or contrary to law. In re Polar Bear,
709 F.3d at 3.

    Of course, whether these levels of genetic connectivity will
be sustained after delisting may be a closer question, but such a
projection is still within the expertise of the Service. Two
Service scientists noted that, because effective dispersals are
hovering just above one-per-generation, “there is not a lot of
wiggle room per assuring effective migration through natural
dispersal into the GYA.” Ed Bangs and Mike Jimenez, Draft
Memo at 3 (May 24, 2011) (“Bangs Memo”). The Service
                                24

nonetheless concluded that “the GYA wolf population will not
be threatened by lower genetic diversity in the foreseeable
future.” Rule, 77 Fed. Reg. at 55,596. It projected that the
overall Northern Rocky Mountain wolf population will stabilize
around 1,000 wolves after delisting in Wyoming. Id. at 55,594.
Although appellees object that the projection has no basis,
especially in light of the states’ documented hostility toward
wolves and their binding commitments only to manage 400
total, in reality, two years after delisting, known 2011
populations remained many times larger than the minimums in
Idaho (746), Montana (653), and the Northern Rocky Mountains
as a whole (1,774). Rule, 77 Fed. Reg. at 55,539. These
population numbers in adjacent states, which offer an indication
of what Wyoming will experience after delisting, provided a
rational basis for the Service to project that the Northern Rocky
Mountain population will level off around 1,000 wolves.

     Appellees still maintain that even if the Service’s projection
is accepted, it was arbitrary to conclude that effective dispersals
will reach one per generation because of the increase in wolf
killings and the paucity of effective dispersals when the
population was under 1,000. As noted, currently known levels
of effective dispersal provide very little cushion above the one-
per-generation threshold, so “very small changes in survival of
a very small proportion of dispersing wolves into Wyoming may
have significant repercussions.” Bangs Memo at 2. The
Secretary explains that the 1,300 square-mile flex area, which
sits across the border from two protected areas in Idaho, was
created to provide a protected corridor for dispersing wolves as
they seek a southern route around the Teton Mountains. The
Secretary also discounts the importance of the expansive
predator area, because it contains little suitable habitat and sits
to the southeast of the GYA subpopulation, while the Montana
and Idaho subpopulations are to the northwest. And the
Secretary allows for the possibility that some dispersing wolves
                                25

will wander into the predator area en route to the GYA, but
concludes “it is certainly not the only or even the likeliest
route.” Fed. Appellants Reply Br. 52; see 77 Fed. Reg. at
55,564.

     Appellees object that the seasonal flex area is too small to
protect migrants, citing a recommendation by Bangs and
Jimenez that the permanent trophy area extend south to Big
Piney, WY. As to length, the flex area is only protected for 4.5
months per year, while an average dispersal takes 5.5 months to
complete, thus ensuring that “the average dispersing wolf [will
pass through] a free-fire zone for at least part of its journey.”
Appellees Br. 70–71. And even in the protected flex area,
appellees point out, dispersing wolves can still be killed by those
holding lethal take or hunting permits. Appellees also refer to
the Service’s conclusion in 2009 that, due to snow depths and
concentration of prey, wolves dispersing into the GYA from the
west were likely to skirt the mountains and “move through the
predatory area.” See Final Rule to Identify the Northern Rocky
Mountain Population of Gray Wolf as a Distinct Population
Segment and To Revise the List of Endangered and Threatened
Wildlife, 74 Fed. Reg. 15,123, 15,176 (Apr. 2, 2009) (“2009
Rule”).

     This aspect of appellees’ challenge too involves some
sleight of hand. The predatory area proposed in 2009 was much
larger (at least 88% of the State) than the current proposal. See
id. The Service had recommended that Wyoming “minimize
take in all suitable habitat and across all of Wyoming’s potential
migration routes,” id., which the current permanent and flex
trophy areas are aimed to accomplish. Rule, 77 Fed. Reg. at
55,564. Moreover, the Service does not dispute that migrants
will enter the predator area, but explains why that would not
preclude dispersals: migrants are harder to locate and kill than
resident wolves, as demonstrated by Idaho hunting data showing
                                26

minimal harvest in areas with few resident wolves even during
peak dispersal season. See id.

     Were genetic connectivity entirely dependent on natural
dispersals, it is possible Wyoming’s current management plan
would prove inadequate due to the apparent closeness to the
minimum threshold in the GYA. But the Service persuasively
responded, pointing out that Wyoming has committed to account
for dispersing wolves when setting quotas, and to collect
samples to monitor for genetic diversity; further, if monitoring
shows that natural dispersals are inadequate, it will modify its
population management program; and if those modifications
prove inadequate over numerous generations, it will employ
human-assisted genetic exchange as a stopgap measure. Rule,
77 Fed. Reg. at 55,595–96. In this way the Rule accounts for,
and protects against, the possibility that natural dispersals could
fall short, or at least it was not arbitrary and capricious for the
Service to so conclude.

     Appellees lastly contend that the ESA’s purpose precludes
the Service from delisting a species where its survival depends
on human-assisted translocation (essentially, trapping a wolf and
trucking it to another subpopulation to breed). This proves too
much. The ESA aims “to provide a program for the
conservation of” endangered and threatened species, 16 U.S.C.
§ 1531(b), by using “all methods and procedures which are
necessary” to bring those species back to the point where the
law’s protections are no longer necessary, id. § 1532(3). From
this purpose, appellees infer a prohibition against delisting if the
ESA’s “methods and procedures” — i.e., “live trapping[] and
transplantation,” id. — are still necessary. Yet if the Service
cannot delist a species when live trapping and transplantation
may still be necessary, the logic of appellees’ interpretation
would mean delisting could not occur if other less invasive
methods like “research, census, law enforcement, [and] habitat
                                27

acquisition” are still necessary. See id. By the same token, the
Secretary’s regulations contemplate delisting even if the species
depends on continued regulatory protection, see 50 C.F.R.
§ 424.11(d), so appellees’ view of the statutory imperative as
allowing only an entirely self-sufficient species to be delisted
can hardly be correct. The authority cited by appellees, Trout
Unlimited v. Lohn, 559 F.3d 946 (9th Cir. 2009), is not to the
contrary. There, the Ninth Circuit concluded that the ESA
requires consideration of the entire species, not just the naturally
hatched portion, and that, in deciding to downlist the species, the
Service rationally considered how the artificially hatched fish
benefit naturally hatched fish. See id. at 957–58. Thus,
downlisting was appropriate even though that decision rested on
the use of “artificial propagation,” one of the ESA’s “methods
and procedures.” See 16 U.S.C. § 1532(3).

     Notably, the Secretary emphasizes that under the Rule
translocation would only be necessary as a last resort, and that
“‘natural connectivity is the preferred approach.’” Fed.
Appellants Reply Br. 54 (quoting 77 Fed. Reg. at 55,565). The
Service expects natural levels of dispersal to be sufficient, so
“wolves in the GYA are not expected to need or rely on human-
assisted migration often, if ever.” Rule, 77 Fed. Reg. at 55,565.
This is not a case, then, in which greater reliance on such
techniques could render a delisting decision arbitrary. It suffices
to conclude that the ESA did not prohibit the Service from
delisting in Wyoming where translocation could eventually be
necessary as a stopgap measure after many generations of
insufficient natural connectivity.

                               B.
      Section 3 of the ESA defines an endangered species as one
in danger of extinction “throughout all or a significant portion
of its range.” 16 U.S.C. § 1532(6). In Wyoming’s predator area
wolves can be killed without restriction, and appellees contend
                               28

it was arbitrary for the Service to conclude this is not a
significant portion of the wolves’ range.

     The predator area contains only 19% of the State’s suitable
habitat, and as of 2011, it contained only 3 of 27 breeding pairs,
8 of 48 packs, and 46 of 328 wolves in Wyoming. Rule, 77 Fed.
Reg. at 55,602. The Service concluded that even if all of those
wolves were killed, the remaining wolves in Wyoming would be
sufficient to maintain a recovered population. Id. As for
dispersing wolves, it acknowledged that some will be killed in
the predator area, but it concluded that even if no dispersing
wolves successfully traversed the Wyoming predator area,
genetic health would not be affected to the point of endangering
the remainder, id. at 55,602–03, due in part to “the current high
level of genetic diversity” in the Northern Rocky Mountain gray
wolf population, id. at 55,596. Thus, according to the Service,
the predator zone cannot be deemed a “significant portion” of
the wolves’ range because the species would not become
endangered even if every single wolf there were killed. Id. at
55,602–03.

     Appellees respond that the Service “cannot have it both
ways, deeming the predator zone insignificant even if all wolves
in the area are killed, but then discounting the genetic-exchange
impacts . . . by speculating that some wolves may survive” their
passage through the predator zone. Appellees Reply Br. 28. But
the Service has not offered “contradictory statements,” see id.,
only complementary ones: it expects that some wolves will
successfully traverse the predator area, but even if that proves
incorrect, genetic health will not decline so much as to endanger
the wolves. Rule, 77 Fed. Reg. at 55,602–03. Appellees’
challenge rests on the mistaken assumption that migrants have
no choice but to traverse the predatory area, making “safe
passage through this area . . . essential to genetic exchange.”
Appellees Br. 78. The rulemaking record is clear, however, that
                              29

wolves can disperse directly into the GYA from Idaho and
Montana “without moving through Wyoming” at all, thereby
accomplishing the desired connectivity goal. Rule, 77 Fed. Reg.
at 55,564; see also id. at 55,534, 55,540.

     Appellees also maintain that the Service irrationally
reversed its 2009 determination that all of Wyoming constituted
a significant portion of the wolves’ range. See 2009 Rule, 74
Fed. Reg. at 15,183. This 2009 determination was deemed
arbitrary and capricious in 2010, see Wyoming v. U.S. Dep’t of
the Interior, Nos. 09-CV-118J & 09-CV-138J, 2010 WL
4814950, at *45 (D. Wyo. Nov. 18, 2010), when based on a
broader, more inclusive definition of “significant portion,”
pursuant to a 2007 opinion of the Solicitor of the Interior that
was later withdrawn. See Fed. Appellants Reply Br. 57. By
contrast, the 2012 Rule is based on the Service’s new, more
restrictive interpretation of the ambiguous phrase “significant
portion” as a portion of the range that would endanger the
species’ survival if removed. See Rule, 77 Fed. Reg. at
55,601–02. Appellees do not challenge the Service’s definition
of “significant portion;” rather, they maintain that even under
that definition the predator area is significant and that the
Service fails to explain the reversal of its 2009 determination.
In 2010, the district court ruled that all of Wyoming was not
appropriately subjected to trophy game management, without
specifying how much of Wyoming could be so designated. In
appellees’ view, then, the factual underpinnings of the 2009
determination are unaffected by the district court’s ruling, and
yet the Service has failed to explain why they are no longer
controlling.

     The 2009 determination has been overtaken by events. Not
only has the Service adopted a new definition of “significant
portion of its range,” see Rule, 77 Fed. Reg. at 55,602–03, but
Wyoming’s regulatory framework has changed, id. at
                              30

55,589–90, and new scientific data has become available in
recent studies, see id. at 55,593 (citing the vonHoldt Study and
the Jimenez Study). Indeed, Hebblewhite has concluded that
vonHoldt’s 2010 study is more comprehensive and robust than
her earlier work showing a lack of genetic connectivity:
“[C]oncerns that this highly vagile and fecund species might
suffer negative effects of genetic isolation . . . have been
effectively laid to rest by vonHoldt et al.’s (2010) exhaustive
work.” Hebblewhite et al., Genetic Connectivity at 4384. The
Service has offered ample rationale for determining that the
predator area was never “envisioned to meaningfully contribute
to wolf recovery in the region” and is thus not a “significant
portion of its range.” Rule, 77 Fed. Reg. at 55,602–03.

     Accordingly, we reverse the judgment vacating the Rule
and otherwise affirm. The court has no occasion to consider the
additional contentions of the Safari Club and NRA that the Rule
reasonably advances conservation efforts and social tolerance
for wolves among hunters and ranchers.
