 United States Court of Appeals
          FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued October 18, 2016                Decided August 1, 2017

                         No. 15-5041

      HUMANE SOCIETY OF THE UNITED STATES, ET AL.,
                     APPELLEES

                               v.

     RYAN ZINKE, SECRETARY OF THE INTERIOR, ET AL.,
                      APPELLEES

     U.S. SPORTSMEN’S ALLIANCE FOUNDATION, ET AL.,
                      APPELLANTS

                STATE OF WISCONSIN, ET AL.,
                        APPELLEES


        Consolidated with 15-5043, 15-5060, 15-5061


        Appeals from the United States District Court
                for the District of Columbia
                    (No. 1:13-cv-00186)


     Joan M. Pepin, Attorney, U.S. Department of Justice,
argued the cause for federal appellants Zinke, et al. With her
on the briefs were John C. Cruden, Assistant Attorney General
at the time the brief was filed, and David C. Shilton, Attorney.
                               2
     Nathan Gambill, Assistant Attorney General, Office of the
Attorney General for the State of Michigan, argued the cause
for appellants State of Michigan, et al. With him on the briefs
were Bill Schuette, Attorney General, Aaron D. Lindstrom,
Solicitor General, and Pamela J. Stevenson, Assistant Attorney
General.

     James H. Lister argued the cause for appellant-defendant-
intervenors Hunter Conservation Coalition, et al. With him on
the briefs were Anna M. Seidman, Douglas S. Burdin, John I.
Kittel, and Michael T. Jean. Jeremy E. Clare and William P.
Horn entered appearances.

     Brad Schimel, Attorney General, Office of the Attorney
General of the State of Wisconsin, Ryan J. Walsh, Chief
Deputy Solicitor General, Daniel P. Lennington, Deputy
Solicitor General at the time the briefs were filed, Jennifer L.
Vandermeuse, Assistant Attorney General, and Thomas J.
Dawson, Assistant Attorney General at the time the brief was
filed, were on the brief for State of Wisconsin and Wisconsin
Department of Natural Resources.

     Kathryn Landrum, Assistant Attorney General, Office of
the Attorney General for the State of Minnesota, was on the
brief for amicus curiae the State of Minnesota in support of
appellants.

     Peter K. Michael, Attorney General, Office of the
Attorney General for the State of Wyoming, James Kaste and
D. David DeWald, Assistant Attorneys General, and Michael
J. McGrady, Assistant Attorney General at the time the brief
was filed, Joseph A. Foster, Attorney General, Office of the
Attorney General for the State of New Hampshire, Douglas A.
Bahr, Solicitor General, Office of the Attorney General for the
State of North Dakota at the time the brief was filed, Sean D.
                               3
Reyes, Attorney General, Office of the Attorney General for the
State of Utah, Cynthia Coffman, Attorney General, Office of
the Attorney General for the State of Colorado, Lawrence G.
Wasden, Attorney General, Office of the Attorney General for
the State of Idaho, Derek Schmidt, Attorney General, Office of
the Attorney General for the State of Kansas, and Timothy C.
Fox, Attorney General, Office of the Attorney General for the
State of Montana, were on the brief for amici curiae the States
of Wyoming, et al. in support of defendants-appellants and
intervenor-defendants-appellants.

     Ralph E. Henry argued the cause for appellees The
Humane Society of the United States, et al. With him on the
brief was Elizabeth Runyan Geise.

     Amy R. Atwood and Collette L. Adkins were on the brief
for amicus curiae Center for Biological Diversity in support of
plaintiffs-appellees The Humane Society of the United States.

    Before: GRIFFITH, MILLETT, and PILLARD, Circuit Judges.

    Opinion for the Court filed by Circuit Judge MILLETT.

     MILLETT, Circuit Judge: The gray wolf once roamed in
large numbers across the contiguous forty-eight States. But by
the 1960s, hunting, depredation, and habitat loss drove the gray
wolf to the brink of extinction, and the federal government
declared the gray wolf an endangered species. After a portion
of the gray wolf population rebounded, the government
promulgated the rule at issue here, which removes from federal
protection a sub-population of gray wolves inhabiting all or
portions of nine states in the Western Great Lakes region of the
United States. The Humane Society of the United States
challenges that rule as a violation of the Endangered Species
Act of 1973 (“Act”), 16 U.S.C. § 1531 et seq., and the
                                4
Administrative Procedure Act (“APA”), 5 U.S.C. § 551 et seq.
Because the government failed to reasonably analyze or
consider two significant aspects of the rule—the impacts of
partial delisting and of historical range loss on the already-
listed species—we affirm the judgment of the district court
vacating the 2011 Rule.

                                I

                                A

      Congress enacted the Endangered Species Act “to halt and
reverse the trend toward species extinction,” and to do so
“whatever the cost.” Tennessee Valley Auth. v. Hill, 437 U.S.
153, 184 (1978). As relevant here, a species is “endangered”
if it “is in danger of extinction throughout all or a significant
portion of its range[.]” 16 U.S.C. § 1532(6). A species is
“threatened” if it “is likely to become an endangered species
within the foreseeable future throughout all or a significant
portion of its range.” Id. § 1532(20).

     The Endangered Species Act directs the Secretary of the
Interior to apply five factors in determining whether a
“species” is endangered or threatened: (i) “the present or
threatened destruction, modification, or curtailment of [the
species’] habitat or range”; (ii) “overutilization [of the species]
for commercial, recreational, scientific, or educational
purposes”; (iii) “disease or predation”; (iv) “the inadequacy of
existing regulatory mechanisms”; and (v) “other natural or
manmade factors affecting [the species’] continued
existence.”     16 U.S.C. § 1533(a)(1).          In making that
determination, the Secretary must rely on “the best scientific
and commercial data available[.]” Id. § 1533(b)(1)(A). The
Secretary of the Interior has delegated the authority to
determine whether a species is “endangered” or “threatened”
                                 5
to the Fish and Wildlife Service (“Service”).            50 C.F.R.
§ 402.01(b).

     The “species” that the Endangered Species Act protects
are defined to include “any subspecies of fish or wildlife or
plants, and,” of most relevance here, “any distinct population
segment of any species of vertebrate fish or wildlife which
interbreeds when mature.” 16 U.S.C. § 1532(16). 1 The Act
does not define “distinct population segment.” Nor do agency
regulations. The Service, however, has issued policy guidance
stating that the existence of a “distinct population segment”
turns upon the discreteness and significance of a sub-
population as compared to the larger species population.
Policy Regarding the Recognition of Distinct Vertebrate
Population Segments Under the Endangered Species Act, 61
Fed. Reg. 4,722, 4,725 (Feb. 7, 1996) (“Segment Policy”). The
Segment Policy emphasizes that the Service’s authority to
recognize distinct population segments should be “exercised
sparingly.” Id. at 4,724.

     To qualify as “discrete” under the Segment Policy, a
domestic animal population must be “markedly separated from
other populations of the same taxon as a consequence of
physical, physiological, ecological, or behavioral factors[.]”
Segment Policy, 61 Fed. Reg. at 4,725. The “significance” of
a potential segment turns on such factors as: (i) the
“[p]ersistence of the discrete population segment in an
ecological setting unusual or unique for the taxon”; (ii)
“[e]vidence that loss of the discrete population segment would
result in a significant gap in the range of a taxon”; (iii)
    1
        The Endangered Species Act defines “species” in a way that
differs from the scientific definition of species. As used in this
opinion, “species” refers to the Act’s definition. The phrase
“taxonomic species” or “taxon” refers to the scientific definition of
a species.
                               6
“[e]vidence 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 (iv) “[e]vidence that the discrete population
segment differs markedly from other populations of the species
in its genetic characteristics.” Id.

     Another key term in analyzing a species’ need for
protection—“range”—is also left undefined by the Act. In
2014, the Service adopted a policy statement defining “range”
as a species’ “‘current range,’ not [its] ‘historical range.’”
Final Policy on Interpretation of the Phrase “Significant
Portion of its Range” in the Endangered Species Act’s
Definitions of “Endangered Species” and “Threatened
Species,” 79 Fed. Reg. 37,578, 37,583 (July 1, 2014) (“Range
Policy”). The Range Policy further explains that a portion of a
species’ range will be considered “significant” if the species
would be in danger of extinction or likely to become so in the
foreseeable future without that portion of its range. Id. at
37,581.

     Once the Service determines that a species is endangered
or threatened, it must add the species to a list of protected
species in the Federal Register. 16 U.S.C. § 1533(c)(1). A
listed species receives robust federal protections, including
prohibitions on possessing, killing, selling, importing, or
exporting its members. Id. § 1538(a). Any person that
knowingly violates those prohibitions faces criminal sanctions,
including fines of up to $50,000 or a year of imprisonment. Id.
§ 1540(b)(1).

     The Act further requires the Service “from time to time
[to] revise” its lists of endangered and threatened species “to
reflect recent determinations, designations, and revisions.” 16
U.S.C. § 1533(c)(1). Every five years, the Service must
                               7
“review * * * and determine * * * whether any such species
should * * * (i) be removed from such list; (ii) be changed in
status from an endangered species to a threatened species; or
(iii) be changed in status from a threatened species to an
endangered species.” Id. § 1533(c)(2)(A), (B).

                               B

                               1

    Regional subspecies of the taxonomic species “gray wolf”
(Canis lupis) were declared endangered by the federal
government between 1966 and 1976. The timber wolf (Canis
lupus lycaon) was first designated as endangered and afforded
protection in 1967, 32 Fed. Reg. 4,001, 4,001 (March 11,
1967), followed by the Northern Rocky Mountain wolf (Canis
lupus irremotus) in 1973, 38 Fed. Reg. 14,678, 14,678 (June 4,
1973). Both the Mexican wolf (Canis lupus baileyi) and the
Texas wolf (Canis lupus monstrabilis) were added to the list in
1976. 41 Fed. Reg. 17,736, 17,737 (April 28, 1976); 41 Fed.
Reg. 24,062, 24,066 (June 14, 1976).

     With the wolves’ numbers rebounding in certain areas, the
federal government in 1978 reclassified the gray wolf from its
regional listings into a single species listing divided into two
groups: Minnesota gray wolves, which the Service determined
had recovered to the point of only being threatened, and the
gray wolf in the remaining forty-seven States, which remained
endangered. See Reclassification of the Gray Wolf in the
United States and Mexico, with Determination of Critical
Habitat in Michigan and Minnesota, 43 Fed. Reg. 9,607, 9,608,
9612 (March 9, 1978) (“1978 Rule”). 2

    2
     Those two groups were listed before the Endangered Species
Act was amended to add “distinct population segments” to the
                                   8

     In 2003, the Service subdivided the gray wolf listing into
three “distinct population segments”: an Eastern segment, a
Western segment, and a Southwestern segment. Final Rule to
Reclassify and Remove the Gray Wolf From the List of
Endangered and Threatened Wildlife in Portions of the
Conterminous United States; Establishment of Two Special
Regulations for Threatened Gray Wolves, 68 Fed. Reg. 15,804,
15,818 (April 1, 2003) (“2003 Rule”). Included in the Eastern
segment were the Minnesota gray wolf population and any gray
wolf population that existed in the Northeast region of the
United States. Id. at 15,859. The Service then designated the
wolves in the Eastern and Western segments as threatened
rather than endangered. Id. at 15,857–15,858, 15,862. The
wolves within the Southwestern segment continued to be listed
as endangered. Id.

     Two district courts struck down the 2003 Rule’s attempted
designation of those three distinct population segments. First,
a district court in Oregon ruled that, by downlisting the species
based solely on the viability of a small population within that
segment, the Service was effectively ignoring the species’
status in its full range, as the Endangered Species Act requires.
See Defenders of Wildlife v. Secretary, U.S. Dep’t of the
Interior, 354 F. Supp. 2d 1156, 1168–1169 (D. Or. 2005). The
2003 Rule thus had the “effect of rendering the phrase
[significant portion of its range] superfluous.” Id. at 1168


definition of “species.” See Endangered Species Act Amendments
of 1978, Pub. L. No. 95-632, 92 Stat. 3,751, 3,752. Prior to the 1978
amendments, the Act defined “species” to “include[] any subspecies
of fish or wildlife or plants and any other group of fish or wildlife of
the same species or smaller taxa in common spatial arrangement that
interbreed when mature.” Endangered Species Act of 1973 § 3, Pub.
L. 93-205, 87 Stat. 884, 886.
                               9
(alteration in original; internal quotation marks and citation
omitted).

     Second, a district court in Vermont concluded that the
Service impermissibly designated and downlisted the Eastern
segment of gray wolves. National Wildlife Fed’n v. Norton,
386 F. Supp. 2d 553, 564–565 (D. Vt. 2005). Fatal to the
Service’s determination, the court concluded, was the Service’s
decision to “lump” into the Eastern segment any gray wolves
in the Northeast region of the United States, without
ascertaining whether a gray wolf population even existed in the
Northeast. See id. In so holding, the court rejected the
Service’s argument that the Endangered Species Act required
it to include any Northeast region wolves in the segment to
avoid turning them into an impermissible “non-DPS remnant”
of gray wolves that neither fell within a recognized segment
nor had independent species or subspecies status of its own. Id.
at 564–565. In the district court’s view, the Service instead
could have continued the remnant’s endangered-species status.
See id. at 565.

                               2

     The government did not appeal either the Oregon or the
Vermont decision. Instead, in what turned out to be the first
round in successive attempts to delist the gray wolves in the
Western Great Lakes area, the Service promulgated a new rule
in 2007 that created a “Western Great Lakes gray wolf distinct
population segment” and simultaneously delisted that segment,
removing it completely from the Endangered Species Act’s
protections. See Final Rule Designating the Western Great
Lakes Populations of Gray Wolves as a Distinct Population
Segment; Removing the Western Great Lakes Distinct
Population Segment of the Gray Wolf From the List of
Endangered and Threatened Wildlife, 72 Fed. Reg. 6,052,
                                10
6,052 (Feb. 8, 2007) (“2007 Rule”). That rule soon met the
same fate as its two predecessors. A district court in this circuit
vacated it for “fail[ing] to acknowledge and address crucial
statutory ambiguities” concerning the creation of distinct
population segments for the purpose of delisting. Humane
Society of the U.S. v. Kempthorne, 579 F. Supp. 2d 7, 9 (D.D.C.
2008); id. at 15. Again, the government did not appeal.

     In December 2008, the Solicitor of the Department of the
Interior issued a memorandum analyzing the statutory
authority for designating distinct population segments for the
specific purpose of delisting them. See U.S. Fish and Wildlife
Service Authority under Section 4(c)(1) of the Endangered
Species Act to Revise Lists of Endangered Species and
Threatened Species to “Reflect Recent Determinations,” Office
of the Solicitor, U.S. Dep’t of Interior (Dec. 12, 2008)
(“Solicitor’s Opinion”). The Solicitor concluded that the Act
unambiguously allows the Service to identify a segment and
then delist it. Id. at 3–5.

     The Solicitor started by noting that, once the Service lists
a species as threatened or endangered, it is obligated to
periodically revise its list of endangered or threatened species
in light of any changes in the conservation status of a species.
Solicitor’s Opinion 3 (citing 16 U.S.C. § 1533(a), (c)(1)). The
Solicitor then reasoned that the Endangered Species Act
imposes no textual limit on the Service’s authority to revise its
list of endangered or threatened species based on intervening
information and determinations. Id. at 4. On that basis, the
Solicitor determined that the Act unambiguously permits the
Service to designate a segment within a listed species,
determine that the segment is no longer endangered or
threatened, and delist it. Id. at 3–5.
                               11
     The Solicitor further opined that, even were the statutory
text ambiguous, his interpretation was a reasonable
construction of the statute and its purposes. Solicitor’s Opinion
5–6. The Solicitor reasoned that, because subspecies and
segments are parts of taxonomic species, any listing of a
taxonomic species necessarily includes a listing of its
constituent segments or subspecies. Id. at 7. On that basis, the
Solicitor concluded that, even if the Service could only delist
an already-listed segment, that requirement would be satisfied
by the listing of the species that encompassed the segment. Id.
The Solicitor also reasoned that delisting a recovered segment
is consistent with the express statutory policies of the Act,
including fostering federal-state cooperation and focusing
resources where they are most needed. Id. at 13–19.

                               3

     Based on the Solicitor’s Opinion, the Service in 2009
republished the 2007 rule without notice and comment, adding
a discussion of “Issues on Remand.” Final Rule To Identify
the Western Great Lakes Populations of Gray Wolves as a
Distinct Population Segment and to Revise the List of
Endangered and Threatened Wildlife, 74 Fed. Reg. 15,070,
15,075 (April 2, 2009) (“2009 Rule”). The Service relied on
the Solicitor’s determination that the Endangered Species Act
permits the Service to “remove an already-listed entity from the
appropriate list in its entirety, or to reduce the geographic or
taxonomic scope of a listing to exclude a group of organisms
previously included as part of an already-listed entity.” Id. at
15,083 (quoting Solicitor’s Opinion 5 n.8).

    Round Two of the Service’s attempt to delist the gray
wolves in the Western Great Lakes area ended in the same
manner as Round One: the 2009 Rule was challenged and
vacated after the Service acknowledged that it had
                               12
impermissibly promulgated the rule without notice and
comment, and agreed to settle the case. Humane Society of the
U.S. v. Salazar, No. 09–1092, Docket Entry No. 27 (D.D.C.
July 2, 2009).

     As a consequence of all those regulatory missteps, the
status of gray wolves remained in 2009 what it had been in
1978: Gray wolves in Minnesota were listed as “threatened,”
while the wolves in the forty-seven other contiguous States
were listed as “endangered.”

                                C

                                1

     This case is Round Three in the Service’s effort to divide
and delist gray wolves in the broader Western Great Lakes
region. In 2011, the Service issued a final rule that, in reliance
on the Solicitor’s Opinion, purported to “revise the boundaries
of the Minnesota” gray wolf population to include the wolves
in all or portions of eight other states. Revising the Listing of
the Gray Wolf (Canis lupus) in the Western Great Lakes, 76
Fed. Reg. 81,666, 81,666, 81,670 (Dec. 28, 2011) (“2011
Rule”). Specifically, the 2011 Rule designated the gray wolf
population in Minnesota, Wisconsin, and Michigan, as well as
portions of North Dakota, South Dakota, Iowa, Illinois,
Indiana, and Ohio, as the Western Great Lakes Distinct
Population Segment. Id. at 81,666, 81,670. In its next breath,
the Service delisted that segment. Id. at 81,723.

     In doing so, the Service again expressly adopted the legal
analysis in the Solicitor’s Opinion regarding its authority to
delist a segment. See 2011 Rule, 76 Fed. Reg. at 81,670,
81,683. The Service then reasoned that, because more than 400
miles existed between the gray wolf population in the Western
                              13
Great Lakes region and other gray wolf packs, the population
qualified as “discrete.” Id. at 81,671. The Service further
found that the loss of the Western Great Lakes population of
gray wolves, which contained “70 percent of North American
gray wolves known to occur south of Canada,” would
constitute a “significant gap in the range” of the “gray wolves
in the United States[.]” Id. at 81,672. The Service thus
concluded that the population qualified as “significant.” Id.
Accordingly, the Service determined that the Western Great
Lakes population of gray wolves constituted a “distinct
population segment.” Id.

     The Service next considered whether the segment was
endangered or threatened throughout all or a significant portion
of its range. 2011 Rule, 76 Fed. Reg. at 81,721–81,723. In
making that determination, the Service explained that it would
interpret “range” to mean “current range.” Id. at 81,722. The
Service also clarified that it would consider a portion of a
species’ range to be “significant” if that portion is “important
to the conservation of the species because it contributes
meaningfully to the representation, resiliency, or redundancy
of the species.” Id.

     Finally, the Service concluded, after analyzing the five
statutory endangerment factors, that the Western Great Lakes
segment was neither endangered nor threatened throughout all
or a significant portion of its range. 2011 Rule, 76 Fed. Reg.
at 81,721–81,723. The Service explained that existing rates of
mortality from disease and human causes had been insufficient
to prevent growth of the population, and that state plans
provided adequate monitoring of and protection for the wolf
segment. See, e.g., id. at 81,694; id. at 81,700.
                               14
                               2

     The Humane Society filed suit alleging that the 2011 Rule
violated both the Endangered Species Act and the APA. The
district court agreed with the Humane Society and vacated the
2011 Rule, concluding that the Endangered Species Act does
not permit the Service to designate a segment only to
immediately delist it. See Humane Society of the U.S. v. Jewell,
76 F. Supp. 3d 69, 110 (D.D.C. 2014). While the district court
agreed that the statutory text was ambiguous, the court
concluded that the Service’s interpretation was unreasonable
given the structure, history, and purpose of the Act. Id. at 110–
113. In the district court’s view, the distinct population
segment designation could only function as a “one-way
ratchet,” allowing the Service to provide more, but not less,
protection for a species. Id. at 112.

     The district court also rejected the Service’s argument that
it was simply revising the prior Minnesota wolf listing when it
created the Western Great Lakes segment. The court explained
that the Minnesota wolves had never been listed as a segment,
and that the newly created segment altered the original
geographic boundaries of the Minnesota wolf population.
Humane Society, 76 F. Supp. 3d at 114–115.

     The district court further concluded that the rule was
arbitrary and capricious because the Service failed to address
how large losses in the gray wolf’s historical range affected the
determination that the Western Great Lakes segment was not
endangered or threatened. Humane Society, 76 F. Supp. 3d at
128–132.

    Finally, the district court held that the rule was invalid
because the Service failed to adequately consider the threat to
wolves from disease and human-caused mortality and the
                               15
insufficiency of state regulatory measures to protect the wolves
after delisting. Humane Society, 76 F. Supp. 3d at 132–134.
The district court accordingly vacated the rule. Id. at 136–137.

                               II

     The Service’s listing determinations are subject to review
under Section 706 of the APA, 5 U.S.C. § 706. See American
Wildlands v. Kempthorne, 530 F.3d 991, 997 (D.C. Cir. 2008).
Under that standard, we must overturn an agency decision if it
is “arbitrary, capricious, an abuse of discretion, or otherwise
not in accordance with law.” 5 U.S.C. § 706(2)(A).

     We review the Service’s interpretation of the Endangered
Species Act under the familiar two-step Chevron framework.
See Chevron U.S.A., Inc. v. Natural Resources Def. Council,
Inc., 467 U.S. 837 (1984). First, we apply the “traditional tools
of statutory construction” to determine whether Congress has
directly spoken to the question at issue. Id. at 842–843 & n.9;
Central United Life Ins. v. Burwell, 827 F.3d 70, 73 (D.C. Cir.
2016). If the statute’s meaning is clear, the inquiry ends and
“we must give effect to the unambiguously expressed intent of
Congress.” Secretary of Labor, Mine Safety & Health Admin.
v. National Cement Co. of Cal., 494 F.3d 1066, 1073 (D.C. Cir.
2007) (internal quotation marks and citation omitted). If,
however, “the statute is silent or ambiguous with respect to the
specific issue,” then we will defer to the agency’s considered
interpretation of the statute if it is “reasonable.” Abington
Crest Nursing & Rehab. Ctr. v. Sebelius, 575 F.3d 717, 719
(D.C. Cir. 2009) (internal quotation marks and citation
omitted); see also United States v. Mead Corp., 533 U.S. 218,
227–229 (2001).

    The central dispute in this case is whether the Endangered
Species Act permits the Service to carve out of an already-
                               16
listed species a “distinct population segment” for the purpose
of delisting that segment and withdrawing it from the Act’s
aegis. We hold that the Act permits such a designation, but
only when the Service first makes the proper findings.

                                A

     This question of statutory interpretation starts with the
Endangered Species Act’s plain text. The Act extends its
protections to an endangered or threatened “species,” and then
defines such protected species to include “any distinct
population segment of any species of * * * wildlife[.]” 16
U.S.C. § 1532(16). The identification and application of the
Act to “distinct population segment[s]” thus falls
straightforwardly within the Service’s wheelhouse. That much
cannot be textually disputed.

     The tougher question is whether that distinct population
segmentation process is, as the district court ruled, a one-way
ratchet that only allows the Service to extend the Act’s
protections to newly recognized groupings. See Humane
Society, 76 F. Supp. 3d at 112. Or can the Service, even after
a species as a whole has been identified as endangered or
threatened, cleave out a subset of that already-listed species for
delisting based on the segment’s recovery (or uplisting if it has
become distinctly imperiled)? Said another way, once a
species has been listed, must any changes in its listing status
occur species-wide or can the species and its status be
dissevered? As to that question, the statutory text is murkier.

    The Endangered Species Act quite plainly allows—
actually, requires—the Service to periodically revisit and, as
warranted, revise the status of a listed species. Section
1533(c)(1) directs the Service to, “from time to time revise
each list * * * to reflect recent determinations, designations,
                                17
and revisions.” 16 U.S.C. § 1533(c)(1); see id. § 1533(a)(1),
(b)(1)(A). And Section 1533(c)(2) separately directs the
Service to “conduct, at least once every five years, a review of
all [then-listed] species,” and to “determine on the basis of such
review whether any such species should—(i) be removed from
such list; (ii) be changed in status from an endangered species
to a threatened species; or (iii) be changed in status from a
threatened species to an endangered species.”                   Id.
§ 1533(c)(2)(A), (B). Each decision made under those two
statutory provisions must rely upon the five statutorily
designated criteria for listing and the best available scientific
and commercial data.           Id. § 1533(c)(1), (2); see id.
§ 1533(a)(1), (b)(1)(A).

     Nothing in that statutory language forbids the recognition
of recovered distinct population segments within a listed
species. The Secretary’s authority to revise a listing under
Section 1533(c)(1) is generally unconditioned, as long as the
underlying determination on which the revision is based (here,
the finding of a distinct population segment) is grounded in the
five statutory listing factors and the best available scientific and
commercial data. See 16 U.S.C. § 1533(c)(1). To be sure,
subsection (c)(1) cross-references the best-evidence
requirement of Section 1533(b)(1)(A), which in turn directs the
Service to “make determinations * * * after conducting a
review of the status of the species,” id. § 1533(b)(1)(A)
(emphasis added). But that leaves textually unanswered the
central question of whether a review of “the species” can itself
result in the identification of a distinct population segment.

    Section 1533(c)(2)’s quinquennial review provision offers
some textual support for the Humane Society’s argument that
a change in status must be made for the species as listed.
Subsection (c)(2) requires reconsideration of whether “such
species” as “included in a list” that is “in effect at the time of
                               18
such review” should be changed from endangered to
threatened, changed from threatened to endangered, or
removed from the list entirely. 16 U.S.C. § 1533(c)(2)
(emphasis added). “[S]uch species” would seem to require
review of the species’ status as listed.

      But while that reading of the statute would be reasonable,
it is not ineluctable. To begin with, while subsection (c)(2)
prescribes what decisions the Service must make, its text does
not foreclose the Service from making additional status
decisions. In other words, nothing in the statutory language
indicates that the mandated decisions are a ceiling capping the
Service’s authority rather than just a minimum-requirements
floor. In addition, subsection (c)(2) does not detract from the
Service’s more open-ended revision authority under subsection
(c)(1).

    The long and the short of all this is that the text of the
Endangered Species Act does not itself answer the question
whether the Service can designate a distinct population
segment from within an already-listed species.

                                B

     Because the statute is “silent or ambiguous with respect to
the specific issue” at hand, the question before this court
becomes whether the Service’s interpretation is “based on a
permissible construction of the statute.” United States Sugar
Corp. v. EPA, 830 F.3d 579, 605 (D.C. Cir. 2016) (quoting
Chevron, 467 U.S. at 842–843). Generally, a “‘reasonable’
explanation of how an agency’s interpretation serves the
statute’s objectives is the stuff of which a ‘permissible’
construction is made[.]” Northpoint Tech., Ltd. v. FCC, 412
F.3d 145, 151 (D.C. Cir. 2005) (citation omitted). “[A]n
explanation that is ‘arbitrary, capricious, or manifestly contrary
                                19
to the statute,’ however, is not.” Id. (quoting Chevron, 467
U.S. at 844). Accordingly, this court must determine whether
the Service “has advanced a reasonable explanation for its
conclusion that the regulations serve * * * [the Act’s]
objectives,” Chevron, 467 U.S. at 863, and whether that
“interpretation * * * is at least reasonable in light of any
ambiguities in the statute[,]” District of Columbia. v.
Department of Labor, 819 F.3d 444, 449 (D.C. Cir. 2016). See
United States Sugar Corp., 830 F.3d at 608 (regulation must
reflect a “permissible reading” of the statute).

    The Service’s interpretation of Section 1533(c)(1) as
allowing for the designation of a distinct population segment
within a listed species is a reasonable reading of statutory text
and—when properly undertaken, see Part II.C, infra—does not
contravene the purposes of the Endangered Species Act.

     With respect to the statutory language, the Service’s
position makes textual sense because subsection (c)(1) itself
expressly contemplates that new “designations” and
“determinations” could intervene that would require
“revis[ing]” an extant listing. 16 U.S.C. § 1533(c)(1).
Furthermore, the listing of an animal at the species-wide level
can reasonably be understood to include within it a listing of
all subspecies and segments within that species. That is to say,
the Service’s initial listing of all gray wolves in North America
necessarily listed all possible segments and subspecies within
that grouping. See Solicitor’s Opinion 7; 2011 Rule, 76 Fed.
Reg. at 81,670, 81,683. So understood, the Service’s
interpretation comports with Section 1533(c)(2)’s textual
requirement that listing changes apply only to species that are
already “included in a list * * * [that] is in effect,” at the time
of the Service’s five-year status review, id. § 1533(c)(2).
                               20
      In addition, the statute requires the Service to attend to
both parts of the listing process—the initial listing, and the
revision or delisting—with equal care. After all, both
subsections (c)(1) and (c)(2) require the Service to rely on the
same factors and best evidence that were first used to list a
species when downlisting, delisting, uplisting, or otherwise
revising that species’ status. Nothing in the statutory text
compels the Service to put a thumb on the scale in favor of
listing, nor does the text require the Service to temporize when
the best evidence indicates that a revision is warranted.

     Indeed, the statutory text leaves room for the Service, at
the initial stage, to list most of a species as threatened, while
dividing out a distinct population segment for listing as
endangered based on its unique circumstances and conditions.
That same language would also permit the Service at the outset
to list a segment as threatened even if the remainder of the
taxon is endangered. See 16 U.S.C. § 1532(16) (defining
“species” in non-exhaustive terms); cf. Modesto Irrigation
Dist. v. Gutierrez, 619 F.3d 1024, 1031–1032 (9th Cir. 2010)
(Service need not place interbreeding populations of a species
in the same distinct population segment); Trout Unlimited v.
Lohn, 559 F.3d 946, 959–961 (9th Cir. 2009) (upholding the
Service’s practice of distinguishing between geographically
co-located hatchery and natural populations of the same
taxonomic species when listing).

     Because the statutory text and purposes can be read to
permit such a divided listing on the front end of the listing
process, the Service likewise can reasonably read the statute to
permit similar determinations at the revision stage. The
statutory text does not have to be treated like a one-way street
leading only to uplisting.
                                21
     The Service’s position is also consonant with the purposes
of the Endangered Species Act, which is to devote needed
resources to the protection of endangered and threatened
species, while abating the Act’s comprehensive protections
when a species—defined to include a distinct population
segment—is recovered. See, e.g., 16 U.S.C. § 1531 (statutory
purpose is to provide for the conservation of species when they
are “endangered” or “threatened”); id. § 1533(b)(2) (directing
the Service to take into account the “economic impact, the
impact on national security, and any other relevant impact”
when designating “any particular area as critical habitat”);
Defenders of Wildlife v. Norton, 258 F.3d 1136, 1144 (9th Cir.
2001) (noting Congress’s desire to allow the Service “more
flexibility in [its] approach to wildlife management”). The
Service’s interpretation ensures that the most resources can be
brought to bear where a species continues to be threatened or
endangered. See Solicitor’s Opinion 18–19; 2011 Rule, 76
Fed. Reg. at 81,670, 81,683. In that regard, the Act’s direction
to the Service to evaluate the status of not just species, but
subspecies and segments, 16 U.S.C. § 1532(16), signals
Congress’s intent to target the Act’s provisions where needed,
rather than to require the woodenly undifferentiated treatment
of all members of a taxonomic species regardless of how their
actual status and condition might change over time. 3

     Another purpose of the Endangered Species Act is to foster
state cooperation in the conservation of threatened or
endangered species. See 16 U.S.C. § 1531(a)(5) (One purpose

    3
       See also 16 U.S.C. § 1539(j) (providing for the discretionary
use of experimental populations in species recovery); id. § 1539(a)
(allowing the Service to issue permits for the “taking” of listed
species in specified circumstances); Loggerhead Turtle v. Council of
Volusia Cty., 148 F.3d 1231, 1260 (11th Cir. 1998) (describing
“flexible” nature of the Service’s authority to allow “incidental
takes”).
                                 22
of the Act is “encouraging the States * * * to develop and
maintain conservation programs which meet national and
international standards[.]”); see also Solicitor’s Opinion 16–17
(“Removing [Endangered Species Act] protections for
recovered [Distinct Population Segments] of listed species
reinforces the strong public policy goal of federal-State
cooperation[.]”); 2011 Rule, 76 Fed. Reg. at 81,670, 81,683
(incorporating the views expressed in the Solicitor’s Opinion). 4
Because the locations of distinct population segments not
uncommonly correspond with geographical lines, empowering
the Service to alter the listing status of segments rewards those
States that most actively encourage and promote species
recovery within their jurisdictions. On the other hand,
continuing to rigidly enforce the Act’s stringent protections in
the face of such success just because recovery has lagged
elsewhere would discourage robust cooperation. The Service’s
interpretation thus reasonably “encourage[s] the States * * *
through * * * a system of incentives.” 16 U.S.C. § 1531(a)(5).

    The Humane Society argues that Service action under the
Act “must be, first and foremost, to provide protections to
endangered or threatened species.” Humane Society’s Br. 33.
True enough. But that premise does nothing to answer the




     4
        See also 16 U.S.C § 1533(b)(1)(A) (directing the Service to
take into account “efforts, if any, being made by any State or foreign
nation, or any political subdivision of a State or foreign nation, to
protect such species, whether by predator control, protection of
habitat and food supply, or other conservation practices, within any
area under its jurisdiction, or on the high seas,” when determining
whether to list a species).
                               23
specific question of whether the Service is permitted to tailor
its protections to where they are most needed.

     Relatedly, the Humane Society argues that designating a
segment to delist it violates the Service’s formal Segment
Policy, 61 Fed. Reg. at 4,724–4,725. Aspects of that Policy
certainly underscore its protective purpose. The Service has
explained that the identification of distinct population
segments should “be aimed at carrying out the purposes of the
Act,” including “to provide a means whereby the ecosystems
upon which endangered species and threatened species depend
may be conserved, [and] to provide a program for the
conservation of such endangered species and threatened
species.” Id. at 4,722 (internal quotation mark and citation
omitted).     Indeed, some of the Policy’s criteria for
“significance”—which a population must possess to qualify as
a segment—would seem to most often be relevant to enhancing
protections for animals. For example, it would not make much
sense to downlist or delist a population that “represents the only
surviving natural occurrence of a taxon that may be more
abundant elsewhere as an introduced population outside its
historic range.” Id. at 4,725.

     On the other hand, other aspects of the Segment Policy
plainly work in both the listing and delisting directions. See
Segment Policy, 61 Fed. Reg. at 4,722 (describing segments as
being used “for the purposes of listing, delisting, and
reclassifying species”) (emphasis added); id. at 4,725 (referring
to the enumerated segment factors as “apply[ing] similarly for
addition to the lists[,] * * * reclassification, and removal from
the lists”) (emphasis added); id. (identifying the Segment
Policy as guiding “the evaluation of distinct vertebrate
population segments for the purposes of listing, delisting, and
reclassifying under the Act”) (emphasis added).
                                24
     The Solicitor’s Opinion, formally adopted by the Service,
has now explicitly interpreted the Act to allow the segment tool
for delisting. See Solicitor’s Opinion 3–5; 2011 Rule, 76 Fed.
Reg. at 81,670, 81,683. See also Encino Motorcars, LLC v.
Navarro, 136 S. Ct. 2117, 2125 (2016) (“Agencies are free to
change their existing policies so long as they provide a
reasoned explanation for the change.”).

     The Humane Society also argues that designating a
segment to delist it violates the specific process set out in the
Segment Policy, 61 Fed. Reg. at 4,725. That Policy identifies
three factors to be considered in designating and listing a
segment: the “discreteness,” “significance,” and “conservation
status” of a population. Id. The Humane Society reads that
provision to require findings that a population is discrete,
significant, and has a conservation status of threatened or
endangered before the Service can designate it.

     But the far more natural reading of the Policy is that it only
requires a determination that the potential segment is
threatened or endangered prior to listing, not prior to the
designation of the segment itself. See Segment Policy, 61 Fed.
Reg. at 4,725. The Policy specifically sets out identification of
the segment’s conservation status as an independent step that
follows after a segment has been identified as a distinct
population segment because of its discreteness and
significance. See id. (“Status: If a population segment is
discrete and significant (i.e., it is a distinct population segment)
its evaluation for endangered or threatened status will be based
on the Act’s definitions of those terms and a review of the
factors enumerated in [Section 1533(a)].”) (second emphasis
                                25
added). The Service’s decision in this case thus did not
contradict its Segment Policy. 5

                           * * * * *

     “When it enacted the [Endangered Species Act], Congress
delegated broad administrative and interpretive power to the
[Service].” Babbitt v. Sweet Home Chapter of Communities for
a Great Oregon, 515 U.S. 687, 708 (1995). And “[t]he task of
defining and listing endangered and threatened species requires
an expertise and attention to detail that exceeds the normal
province of Congress.” Id. Given the ambiguity of the
statutory text, the Humane Society’s proffered interpretation of
the Act as favoring the use of segments in a protective manner
may very well be reasonable. But our task under Chevron is
not to pick from amongst reasonable options. Our task is
simply to determine whether the Service’s interpretation of the
ambiguous language is reasonable. We hold that the Service
permissibly concluded that the Endangered Species Act allows
the identification of a distinct population segment within an
already-listed species, and further allows the assignment of a
different conservation status to that segment if the statutory
criteria for uplisting, downlisting, or delisting are met.


    5
        Because the Service has the better and more natural reading
of its Segment Policy, we do not address whether the Service’s
interpretation is owed deference under Auer v. Robbins, 519 U.S. 452
(1997). Cf. Baptist Mem’l Hosp.-Golden Triangle v. Sebelius, 566
F.3d 226, 228 (D.C. Cir. 2009) (“We need not tackle the question of
[Auer] deference: We agree with the Board’s interpretation of its
Instructions regardless of what, if any, deference we owe it in this
case.”); see also Talk America, Inc. v. Michigan Bell Tel. Co., 564
U.S. 50, 67 (2011) (Scalia, J., concurring) (“In this suit I have no
need to rely on Auer deference, because I believe the [agency’s]
interpretation is the fairest reading of the orders in question.”).
                               26
                                C

     Holding that the Service has the legal authority to identify
a distinct population segment from within an already-listed
species does not mean it did so properly here. In fact, it did
not. The fundamental error in the Service’s decision is that, in
evaluating whether gray wolves in the Western Great Lakes
region are a “distinct” population segment, the Service failed
to address the impact that extraction of the segment would have
on the legal status of the remaining wolves in the already-listed
species. More specifically, the Service cannot find that a
population segment is distinct—in the Service’s words, that it
is severable because it is “discrete” and “significant”—without
determining whether the remnant itself remains a species so
that its own status under the Act will continue as needed.

                                1

     The Endangered Species Act’s text requires the Service,
when reviewing and redetermining the status of a species, to
look at the whole picture of the listed species, not just a
segment of it. Section 1533(c)(2)(A) requires that the review
cover the “species included in a list.”               16 U.S.C.
§ 1533(c)(2)(A); see also id. § 1533(c)(1), (b)(1)(A) (directing
the Service, when revising the status of a species, to “make [its]
determinations * * * after conducting a review of the status of
the species” as listed) (emphasis added); see also id.
§ 1533(c)(2)(B). As the Service itself argues, that review can
reasonably be read to include any and all of the composite
segments or subspecies that might be included within a
taxonomically listed species. See Solicitor’s Opinion 7–8 &
n.10; 2011 Rule, 76 Fed. Reg. at 81,670, 81,683. Thus, when
a species is already listed, the Service cannot review a single
segment with blinders on, ignoring the continuing status of the
species’ remnant. The statute requires a comprehensive review
                                27
of the entire listed species and its continuing status. Having
started the process, the Service cannot call it quits upon finding
a single distinct population segment.

    The Service’s definition of a “distinct population segment”
confirms the point. See Segment Policy, 61 Fed. Reg. at 4,725.
The Service’s two critical criteria for such a segment are
“discreteness” and “significance.” Id. Both of those factors
must be met before a segment can be recognized.

    To start, the Service looks at the “[d]iscreteness of the
population segment in relation to the remainder of the species
to which it belongs.” Segment Policy, 61 Fed. Reg. at 4,725.
More specifically, to be distinct, a segment must be “markedly
separated” out “from other populations of the same taxon as a
consequence of physical, physiological, ecological, or
behavioral factors.” Id. Those two factors clearly envision a
comparative analysis of a potential segment to the remnant and
consideration of the segment’s independent severability. 6

     With respect to the “significance” part of the test, the
Service looks to such factors as whether the segment:
(i) persists in an “ecological setting” that is “unusual or unique
for the taxon”; (ii) is the “only surviving natural occurrence of
a taxon”; (iii) has genetic characteristics that are “markedly”
different from the rest of the taxon; or (iv) would cause a
“significant gap” in the taxon’s range if lost. Segment Policy,
61 Fed. Reg. at 4,725. Each of those factors measures a
potential segment’s “significance” in relation to the “taxon.”
That means that an evaluation of “significance” presupposes
that there is a still-existing taxon against which to compare the

    6
        International borders can also sometimes help to identify a
discrete population segment. Segment Policy, 61 Fed. Reg. at 4,725.
That consideration is not at issue in this case.
                               28
potential segment. Indeed, without an evaluation of the taxon
(both pre- and post-designation of the proposed segment), the
Service could not in any meaningful way evaluate the proposed
segment’s significance to that taxon.

     Requiring the Service to look at the implications for both
the segment and the remnant during the delisting, uplisting, or
downlisting process thus flows naturally from the Endangered
Species Act’s text and the Service’s own Segment Policy.

      Even more importantly, omitting analysis of the effect of
designation on the already-listed species would divest the
extant listing of legal force. The segment-designation process
is meant to be “sparing[]” in its use. Segment Policy, 61 Fed.
Reg. at 4,724. Yet the Service’s disregard of the remnant’s
status would turn that sparing segment process into a backdoor
route to the de facto delisting of already-listed species, in open
defiance of the Endangered Species Act’s specifically
enumerated requirements for delisting. See 16 U.S.C.
§ 1533(a)(1) (listing five mandatory criteria for altering a
listing). Accordingly, as a matter of plain statutory design, the
act of designating a segment cannot in one fell swoop make an
already-listed species an unlisted and unlistable non-species,
“sidestep[ping]” the process “Congress has plainly” prescribed
for delisting. See Natural Resources Def. Council v. EPA, 489
F.3d 1364, 1372 (D.C. Cir. 2007); see also Whitman v.
American Trucking Ass’ns, 531 U.S. 457, 485 (2001) (“[An
agency] may not construe the statute in a way that completely
nullifies textually applicable provisions meant to limit its
discretion.”). Instead, the Service must make it part and parcel
of its segment analysis to ensure that the remnant, if still
endangered or threatened, remains protectable under the
Endangered Species Act.
                              29
                              2

     In designating the Western Great Lakes wolves as a
distinct population segment, the Service looked only at the
characteristics of the Western Great Lakes segment in a
vacuum, ignoring the second step of determining whether both
the segment and the remainder of the already-listed wolves
would have mutually independent statuses as species.

     Prior to the 2011 Rule designating the Western Great
Lakes segment, the Service had made two listings of gray
wolves: those in Minnesota that were found to be threatened,
and those wolves in the lower forty-eight states outside of
Minnesota that were determined to be an endangered species.
When the Service attempted to carve the Western Great Lakes
segment out of the latter, it left the remnant of that already-
statutorily-protected group in legal limbo without any
determination that the gray wolves in the continental United
States outside of the Western Great Lakes segment were
themselves a species, subspecies, or segment that could
continue to be protected under the Endangered Species Act.
Certainly “gray wolves outside the Western Great Lakes
segment” have never been recognized as a taxonomic species.
The Service also failed to analyze whether “gray wolves
outside the Western Great Lakes segment” are either a
subspecies or a segment. 7 Absent such a determination, the
Service has left entirely unexplained how the remaining
wolves’ existing endangered status would continue. Nor did
the Service make any finding that the remnant was no longer
endangered under the statutory listing criteria.



    7
       We take no position on whether such a designation by the
Service would be appropriate. See Florida Power & Light Co. v.
Lorion, 470 U.S. 729, 744 (1985).
                               30
     Worse still, the Service has announced that, with the
Western Great Lakes segment carved out, the remnant is no
longer a protectable “species” and has proposed its delisting for
that reason alone. See Removing the Gray Wolf (Canis lupus)
From the List of Endangered and Threatened Wildlife and
Maintaining Protections for the Mexican Wolf (Canis lupus
baileyi) by Listing It as Endangered, 78 Fed. Reg. 35,664,
35,668 (June 13, 2013) (“We conclude that the current C. lupus
[gray wolf] entity is not a valid species under the Act and now
propose to remove this entity from the List[.]”). The Service
did not deny that position at oral argument. See Oral Arg. Tr.
85–90.

     The Service’s power is to designate genuinely discrete
population segments; it is not to delist an already-protected
species by balkanization. The Service cannot circumvent the
Endangered Species Act’s explicit delisting standards by riving
an existing listing into a recovered sub-group and a leftover
group that becomes an orphan to the law. Such a statutory
dodge is the essence of arbitrary-and-capricious and ill-
reasoned agency action. See Ragsdale v. Wolverine World
Wide, Inc., 535 U.S. 81, 91–92, 94 (2002) (invalidating agency
action that constituted an “end run around important [statutory]
limitations” and thus “contravene[d] Congress’ will” and
“subvert[ed] the careful balance” of the statute).

    The Service argues in the alternative that it did not
designate a new segment, but rather only revised the 1978
Minnesota gray wolf segment and then delisted it. We are
doubtful that the Service’s action can be fairly characterized as
a revision, especially given the fact the purported revision
roped-in wolf populations outside of the original Minnesota
population. See 2011 Rule, 76 Fed. Reg. at 81,678–81,679,
81,716; 1978 Rule, 43 Fed. Reg. at 9,608 (“There is also a
group [of wolves] on Isle Royale in Lake Superior, and
                               31
possibly a few scattered individuals in northern Michigan and
Wisconsin.”). By bringing within the scope of the segment
those outside-Minnesota wolves, the Service’s “revision” of
the Minnesota gray wolf segment is in fact a revamping of the
entire gray wolf listing, including the non-Minnesota
population listing. But we need not decide that question.
Whether labeled a revision or a segment-designation, the flaw
is the same: the failure to address the status of the remnant is
fatal.

                               III

      Under the Endangered Species Act, the determination of a
species’ endangered or threatened status turns on the threats
that the species faces “throughout all or a significant portion of
its range.” 16 U.S.C. § 1532(6), (20). The Service concluded
that “range” refers to the species’ current range at the time its
status is evaluated or reevaluated for listing. See 2011 Rule, 76
Fed. Reg. at 81,721–81,722. The district court held that the
Service’s decision to delist the Western Great Lakes segment
failed to adequately address the wolves’ loss of historical
range. Humane Society, 76 F. Supp. 3d at 128–132. Because
the Service’s interpretation of “range” as focusing on “current
range” is reasonable, we uphold it. But because the Service
categorically excluded the effects of loss of historical range
from its analysis, we hold that the Service’s conclusion about
the ongoing threat to the Western Great Lakes segment within
its current range was insufficiently reasoned, and therefore
arbitrary and capricious.

                                A

     Under Chevron, we ask first whether the Endangered
Species Act speaks directly to the meaning of “range” and, if it
does not, we must evaluate the reasonableness of the Service’s
interpretation. See 467 U.S. at 842–843.
                                32
     The Endangered Species Act does not itself define
“range.”     See 16 U.S.C. § 1532.            The definitions of
“endangered” and “threatened” species, however, do use the
present tense “is” to refer to the status of the species within its
range. Id. § 1532(6), (20). That seems to accord with the
Service’s position that “range” refers to “current range.” See
Sherley v. Sebelius, 644 F.3d 388, 394 (D.C. Cir. 2011) (“The
use of the present tense in a statute strongly suggests it does not
extend to past actions.”). But see McNeill v. United States, 563
U.S. 816, 821–822 (2011) (Congress has “used the present
tense to refer to past convictions”).

     Still, focusing on verb tense does not get the Service very
far. That is because the placement of “is” in the definitions
seems most naturally to require that the species currently be
endangered or threatened within its range, not to dictate the
temporal scope of geographical evidence the Service is to
consider. A species can be found to be endangered now—“is
in danger of extinction,” 16 U.S.C. § 1532(6) (emphasis
added)—based just as easily on threats to the species
throughout its historical range as on threats throughout its
contemporary range. Cf. Defenders of Wildlife v. Norton, 258
F.3d 1136, 1145 (9th Cir. 2001) (“[A] species can be extinct
‘throughout * * * a significant portion of its range’ if there are
major geographical areas in which it is no longer viable but
once was.”) (second alteration in original).

     Outside of its use in the definitions of “endangered” and
“threatened” species, “range” appears only three times in the
Act. The term first appears in Section 1533(a), which lists “the
present or threatened destruction, modification, or curtailment
of [a species’] habitat or range,” as one of several factors for
the Service to consider in determining “endangered” or
“threatened” status. 16 U.S.C. § 1533(a)(1)(A). The term
appears a few subsections later in Section 1533(c), which
                               33
mandates that the listing of a species as endangered or
threatened shall “specify with respect to each * * * species
over what portion of its range it is endangered or threatened,
and specify any critical habitat within such range.” Id.
§ 1533(c)(1). Neither of those usages casts material light on
the meaning of “range” because the two references are as
textually indeterminate as the initial use of the term in Section
1532.

     The third place that “range” appears is in Section 1539(j),
which provides that the Secretary may authorize the release of
any population of an endangered or threatened species “outside
the current range of such species if the Secretary determines
that such release will further the conservation of such species.”
16 U.S.C. § 1539(j)(2)(A). That provision cuts both ways. On
the one hand, it could be argued that, if “range” already means
current range, then the adjectival addition of “current” in
Section 1539(j) would be redundant. On the other hand, the
use of “current range” in Section 1539(j) could also be read to
corroborate the Service’s view, since “current range” in
Section 1539(j) may refer to the listed range of the endangered
or threatened species. See id. § 1539(j)(2)(A).

     Dictionary definitions do not illuminate the meaning of
“range” either. As a biological and zoological term of art,
“range” is commonly defined as a geographical reference to the
physical area in which a species lives or occurs. See, e.g., 8
THE OXFORD ENGLISH DICTIONARY 139 (def. 7) (1933)
(defining “range” as: “[t]he geographical area over which a
certain plant or animal is distributed”). The most that can be
said is that such dictionary definitions employ the present
tense. But that may reflect the nature of dictionary definitions
                                  34
generally, rather than suggest any contextual meaning within
the Endangered Species Act. 8

     Accordingly, traditional rules of statutory construction do
not answer the question of whether “range” means current or
historical range. Indeed, the Service and the Humane Society
both acknowledge that the Act leaves open the possibility that
“range” may refer to either current or historical range. See
Service’s Br. 68–69; Humane Society’s Br. 47–48. 9 The
question then becomes whether the Service’s interpretation of
“range” as “current range” “is based on a permissible
construction of the statute.” Mayo Found. for Med. Educ. &
Research v. United States, 562 U.S. 44, 54 (2011) (quoting
Chevron, 467 U.S. at 843). It is.

     Although the statute itself does not indicate the meaning
of “range,” the Service’s interpretation is at least consistent
with the Endangered Species Act’s use of the present tense in
provisions discussing the species’ range, 16 U.S.C. § 1532(6),
(20). And it also accords with Section 1539(j)(2)(A)’s use of
“current range” in reference to a species’ listed range. In
addition, focusing on the species’ survival in the range it
currently occupies is consonant with the purposes of the
Endangered Species Act, because the threats that a species
confronts where it currently lives often affect its continued

     8
      None of the parties suggests that legislative history illuminates
the meaning of “range.”
     9
        Other courts have recognized the ambiguity of the broader
statutory phrase “in danger of extinction throughout * * * a
significant portion of its range,” see Defenders of Wildlife, 258 F.3d
at 1141, or “significant portion of its range,” see Colorado River
Cutthroat Trout v. Salazar, 898 F. Supp. 2d 191, 201–203 (D.D.C.
2012); WildEarth Guardians v. Salazar, 741 F. Supp. 2d 89, 99–100
(D.D.C. 2010).
                               35
survival the most and thus bear influentially on whether it
should be listed. See 2011 Rule, 76 Fed. Reg. at 81,722–81,723
(discussing threats in areas where the Western Great Lakes
wolf population currently lives).

     For those reasons, we conclude that the Service’s
interpretation of “range” to focus on a species’ current range is
a reasonable interpretation of the Act.

                               B

     As with the Service’s designation of distinct population
segments, the rub in this case is not with the Service’s
interpretation of the statute, but with its application of the
statute to the record at hand. While analysis of the
reasonableness of agency action “under Chevron Step Two and
arbitrary and capricious review is often the same,”
Pharmaceutical Research & Mfrs. of America v. Federal Trade
Comm’n, 790 F.3d 198, 209 (D.C. Cir. 2015) (internal
quotation marks and citation omitted), the Venn diagram of the
two inquiries is not a circle. The question thus remains whether
the agency arbitrarily and capriciously “‘failed to consider an
important aspect of the problem’ it faces.” SecurityPoint
Holdings, Inc. v. Transportation Sec. Admin., 769 F.3d 1184,
1187 (D.C. Cir. 2014) (quoting Motor Vehicle Mfrs. Ass’n of
the U.S. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43
(1983)).

     We hold that the Service’s analysis of the status of the
Western Great Lakes segment within its current range wrongly
omitted all consideration of lost historical range. Just because
the Endangered Species Act does not compel the Service to
interpret “range” to mean historical range, that does not mean
that the Service can brush off a substantial loss of historical
range as irrelevant to the species’ endangered or threatened
                               36
status. So says the Service itself: The Service’s Range Policy
is explicit that a species may be “endangered or threatened
throughout all or a significant portion of its current range
because [a] loss of historical range is so substantial that it
undermines the viability of the species as it exists today.”
Range Policy, 79 Fed. Reg. at 37,584 (emphasis added).

     That is an eminently sensible approach. Range loss can
“result[] in a species for which distribution and abundance is
restricted, gene flow is inhibited, or population redundancy is
reduced to such a level that the entity is now vulnerable to
extinction or likely to become so within the foreseeable future
throughout all or a significant portion of its current range.”
Range Policy, 79 Fed. Reg. at 37,584. In addition, “a species
with a reduced range is at greater risk of all or most of its
populations being affected by a catastrophic event such as a
hurricane or fire.” Id.

     In other words, an adequate evaluation of the threats
confronting the survival of a species within its current range
requires looking at more than just the current moment in time.
The Service, consistent with its own Range Policy, also needs
to consider the scope of the species’ historical range, and the
impact that material contraction or relocation might indicate for
survival within a currently constricted or confined range.

     There is, moreover, no question in this case that “gray
wolves have been extirpated from most of the southern portions
of their historical North American range.” 2011 Rule, 76 Fed.
Reg. at 81,672. The Humane Society estimates that 95% of the
gray wolf’s historical range has disappeared. Humane
Society’s Br. 48, 50. The Service does not dispute that figure.

    Despite immense losses in the gray wolves’ historical
range—including the historical range of those wolves now
occupying the Western Great Lakes area—the Service nowhere
                               37
analyzed the impact of that loss on the survival of the gray
wolves as a whole, the gray wolves remnant, or the Western
Great Lakes segment. Such a failure to address “an important
aspect of the problem” that is factually substantiated in the
record is unreasoned, arbitrary, and capricious decisionmaking.
State Farm, 463 U.S. at 43; see also AEP Tex. N. Co. v. Surface
Transp. Bd., 609 F.3d 432, 441 (D.C. Cir. 2010) (agency acted
arbitrarily and capriciously when it “failed to address the
unique circumstances of” an issue).

     The Service does not deny the gap in its analysis. Instead,
the Service points to its determination that the Western Great
Lakes segment would remain viable in key portions of the
Western Great Lakes area. See 2011 Rule, 76 Fed. Reg. at
81,722–81,723. That is a non sequitur. As the Range Policy
explained, consideration of material changes in a species’
historical range is critical to a reliable assessment of
sustainability within the current range. So whatever the
Service prognosticates about future viability in certain portions
of the current range cannot be reliably reasoned if it was made
in a historical vacuum. An important factor—the possible
enduring consequences of significant loss of historical range—
was left out of the analysis all together.

     The Service also argues that the Act does not require the
restoration of a species to its entire historical range. See
Service’s Reply Br. 27–29. Okay. But giving adequate
consideration to the effects of large losses of historical range
on a species’ survival going forward has nothing to do with
where geographically a species must be restored. The only
obligation at issue here is for the Service to contend with the
implications of massive range loss for the species’ endangered
or threatened status within its current environment.
                              38
    Finally, we note that, in undertaking that omitted analysis
on remand, the Service will have to grapple with predicate
questions that the Service has evaded thus far, such as:

        •   Defining the physical boundaries of the relevant
            historical range, compare 2011 Rule, 76 Fed. Reg.
            at 81,672 (noting that “[g]ray wolves once lived
            throughout most of North America”), with id. at
            81,689 (finding that this particular population of
            gray “wolves historically occupied the entire
            Midwest”), and id. at 81,725 (describing the gray
            wolf’s historical range as the entire “Holarctic”
            region); see also id. at 81,687 (noting that research
            into “whether gray wolves * * * historically
            occupied portions of the eastern United States is
            ongoing”); and

        •   Establishing the appropriate timeframe for
            measuring a species’ historical range, such as the
            enactment of the 1973 Endangered Species Act,
            the enactment of its predecessor statutes in 1966
            and 1969, the Nation’s founding, or some other
            date.

     In sum, because the undisputedly vast loss of historical
range is a salient factor in determining the endangered or
threatened status of the Western Great Lakes segment and the
remnant population within their current ranges, the Service’s
wholesale failure to address that factor renders the Service’s
decision unreasoned, arbitrary, and capricious.
                              39
                              IV

     The Humane Society also argues that the final rule failed
adequately (i) to explain why the wolf population’s combined
mortality from humans and disease is not a continuing threat to
the species’ existence, and (ii) to address the lack of adequate
plan provisions or other protections for the gray wolves in the
seven States that make up the Western Great Lakes area.
Neither argument succeeds.

                               A

     With respect to the combined threat to the gray wolves’
survival from disease and human-caused death, the record
reflects that the Service adequately wrestled with both
problems and grounded its decision in substantial evidence.

                               1

     With respect to disease mortality, the 2011 Rule addressed
five diseases that afflict the Western Great Lakes gray wolves:
canine parovirus, sarcoptic mange, lyme, dog louse, and canine
distemper virus. The Rule also looked at the possibility of
other diseases entering the wolf population. 2011 Rule, 76 Fed.
Reg. at 81,694–81,698. The Service’s analysis was grounded
in scientific literature specifically analyzing the history and
impact of disease on the gray wolf population.

     For instance, the Service explained that there was “no
evidence” that canine parovirus “caused a population decline
or has had a significant impact on the recovery of the
Minnesota wolf population.” 2011 Rule, 76 Fed. Reg. at
81,694. While some studies suggested that canine parovirus
had reduced pup survival from 1984 to 2004, the Service found
that there had actually been an increase in pup survival since
1995. Id. Notably, data in Wisconsin showed only a single
                              40
pup death attributable to canine parovirus since 2001, id., and
no such deaths in Michigan, id. at 81,695.

     With respect to sarcoptic mange, the Service determined
that mange mortality was “stabilizing or perhaps declining in
Wisconsin.” 2011 Rule, 76 Fed. Reg. at 81,695. The Service
pointed to studies indicating that mange infection had not
increased in Minnesota since 2003, and had in fact declined
from 17% in 2006 to 10% in 2008. Id. at 81,696. As for lyme
disease and dog louse, the Service reported that there had been
no confirmed deaths in the Minnesota wolf population from
dog louse and no reports of clinical symptoms of lyme disease.
Id. Finally, with respect to canine distemper virus, the Service
relied on scientific studies that “predict periodic short-term
declines * * * but no long-term threat to the wolf population”
from the disease. Id.

     The Service also acknowledged the possibility that new
diseases might arise, but concluded there was no sufficiently
concrete risk to threaten the gray wolf’s survival. 2011 Rule,
76 Fed. Reg. at 81,696. In that regard, the Service explained
that Minnesota’s, Michigan’s, and Wisconsin’s state plans all
provided for the continued monitoring of dead wolves and
testing of live-captured wolves and wolf feces to detect any
new diseases that might require intervention. Id. at 81,697.
Looking at the collective threat from disease, the Service
concluded that “the overall trend for wolf populations in the
[Western Great Lakes segment] continues to be upward.” Id.
at 81,698. The Service added that delisting the wolves “will
not significantly change the incidence or impacts of disease and
parasites on these wolves.” Id.

     The Service’s judgment was corroborated through peer
review by a veterinary pathologist specializing in wolf disease
and mortality. The pathologist concluded that the proposed
                               41
rule “definitely contain[ed] an accurate, comprehensive
synthesis of published and unpublished data on disease and
predation threats to the Western Great Lakes * * * wolf
populations.” J.A. 881. She further concurred that “wolf
populations have grown despite introductions of new
diseases,” and that “all evidence indicate[d] that [diseases] are
not likely to endanger the [Western Great Lake] wolf
populations if delisted.” Id.

                               2

     The Service’s analysis of human-caused mortality too was
satisfactory. Human-caused mortality for wolves comes in
three forms: fatal accidents (often involving vehicles), legal
depredation programs, and intentional illegal killings.

    The Service’s 2011 Rule studied human-caused mortality
in detail. The Service reviewed existing mortality data and
acknowledged that humans were responsible for 56% of
diagnosed deaths of radio-collared wolves in Wisconsin from
1979 to 2009, 69% of such deaths in Minnesota from 1994 to
2005, and 75% of such deaths in the Upper Peninsula of
Michigan from 1960 to 1997. 2011 Rule, 76 Fed. Reg. at
81,698–81,699.

     The Service nevertheless concluded that human-caused
mortality was not a significant threat to the wolf’s survival, as
shown by the resilient growth of the gray wolf population
despite the human-caused deaths. “As long as other mortality
factors do not increase significantly,” the Service concluded,
and “monitoring is adequate to document, and if necessary
counteract, the effects of excessive human-caused mortality
should that occur, * * * [the] wolf population will not decline
to nonviable levels” because of human-caused mortality. 2011
Rule, 76 Fed. Reg. at 81,700 (citation omitted).
                              42
     The Service further reasoned that delisting the segment of
gray wolves would not affect the rate of human-caused
mortality. That is because accidental and depredation deaths
are most directly tied to the wolves’ proximity to areas densely
populated by humans. See 2011 Rule, 76 Fed. Reg. at 81,700
(“[A] continuing increase in wolf mortalities from vehicle
collisions, both in actual numbers and as a percent of total
diagnosed mortalities, is expected as wolves continue their
colonization of areas with more human developments and a
denser network of roads and vehicle traffic.”). Additionally,
the Service looked to Minnesota depredation data from 2007
and 2008 (the time when the Western Great Lakes wolf
population was temporarily delisted under the now-vacated
2007 Rule), and found that the rates of depredation deaths did
not change materially from before the wolves were delisted. Id.
at 81,704 (noting that 133 Minnesota wolves were killed in
2007 and 143 wolves in 2008, compared to 134 in 2005 and
122 in 2006). The Service further found that the Western Great
Lakes wolf population continued to grow despite the increase
in depredation deaths in 2007 and 2008 in Wisconsin and
Michigan. See id. at 81,708 (noting that the Wisconsin wolf
population increased 12% between 2008 and 2009); id. at
81,712 (noting that the Michigan wolf population grew 11%
between 2008 and 2009).

     The Service also addressed the problem of illegal killings.
The Service candidly acknowledged the limited data available
since such killings “generally occur in remote locations and the
evidence is easily concealed[.]” Final Rule, 76 Fed. Reg. at
81,698. Nevertheless, the data that the Service was able to
collect indicated that the number and proportion of wolves
killed illegally in Wisconsin declined while the gray wolf was
delisted under the later-vacated 2007 Rule. See id. at 81,696
(showing 17 of 72 wolves found dead in 2006 had been killed
illegally and 20 of 72 in 2009, compared to 10 of 90 in 2007
                              43
and 14 of 94 in 2008); id. (illegal killings were 67% of all
mortality in 2006, 62% in 2006, and 44% in 2010 compared to
19% in 2007 and 23% in 2008). Other than that, the Service
concluded that it was “not possible at this time to determine if
human-caused mortality (apart from mortalities from
depredation control) has significantly changed over the nearly
35-year period that the gray wolf has been listed as threatened
or endangered.” Id. at 81,700.

     What ultimately proved most relevant to the Service was
that, over all of the studied time periods, “all sources of wolf
mortality, including legal (for example, depredation control)
and illegal human-caused mortality, have not been of sufficient
magnitude to stop the continuing growth of the wolf
population[.]” 2011 Rule, 76 Fed. Reg. at 81,700; see also id.
(“Despite human-caused mortalities of wolves in Minnesota,
Wisconsin, and Michigan, these wolf populations have
continued to increase in both numbers and range.”).

     In short, the record supports the Service’s conclusion that
disease- and human-caused mortality have not materially
threatened the expansion of the gray wolf population in the
Western Great Lakes region, and thus the Service reasonably
concluded that those factors do not counsel against delisting.
See Rossello ex rel. Rossello v. Astrue, 529 F.3d 1181, 1185
(D.C. Cir. 2008) (“Substantial-evidence review is highly
deferential to the agency fact-finder, requiring only ‘such
relevant evidence as a reasonable mind might accept as
adequate to support a conclusion.’”) (quoting Pierce v.
Underwood, 487 U.S. 552, 565 (1988)).

    The Service further noted that state plans in Minnesota,
Michigan, and Wisconsin would monitor wolf disease and
mortality, providing an important backstop should new threats
emerge. See 2011 Rule, 76 Fed. Reg. at 81,697. The veterinary
                               44
pathologist peer reviewer agreed that the state plans would
adequately monitor and protect against new disease threats.
Finally, the data evidenced that mortality rates due to disease
and depredation would not be affected in any significant
measure by delisting. Id. at 81,700–81,701.

    The Service’s analysis also answers the Humane Society’s
concern about the combined impact of disease and human-
caused mortality. The simple reality is that both disease- and
human-caused deaths have been simultaneously afflicting the
wolves, and yet the population has continued to grow
nonetheless.

                               B

     The district court also held that the 2011 Rule is arbitrary
and capricious because the Service failed to adequately address
what it described as an “unregulated killing zone” in Minnesota
and the lack of state regulatory plans to monitor and protect the
wolves in six of the Western Great Lakes States. Humane
Society, 76 F. Supp. 3d at 134–136. We again conclude that
the Service’s decision was reasonable and grounded in
substantial evidence.

                               1

     With respect to the Minnesota state plan, what the district
court labeled an “unregulated killing zone” refers to
depredation controls in one particular area of the State. The
Minnesota Plan divides the State into two zones. Within Zone
A, an area covering Northeastern Minnesota and the core of the
wolves’ territory, wolves can only be legally killed in defense
of a human life, in situations of “immediate threat” to the life
of a guard animal or domestic pet, or immediately after a
verified loss of livestock, domestic animals, or pets. See MINN.
STAT. § 97B.645, subdivs. 3, 5, 6. An “immediate threat” is
                               45
defined as a wolf stalking, attacking, or killing. See id.
§ 97B.645, subdiv. 12(c). Within this zone, a “control area”
can be opened immediately following the government’s
verification of the loss of livestock, domestic animals, or pets.
See id. § 97B.671, subdiv. 4(c). However, the control area can
only be opened for sixty days, and it must be within a one-mile
radius of the site of the loss. See id. § 97B.671, subdiv. 4(c),
(d). Trained and certified predator controllers will be paid
$150 for each wolf they kill within the control area. In
addition, owners of livestock and domesticated animals within
Zone A may shoot or destroy a wolf that poses “an immediate
threat” to such animals “on property owned, leased or occupied
by the owner” of the animal. Id. § 97B.645, subdiv. 5.

     Likewise, in Zone B, a controlled killing area can be
opened following a verified loss of livestock, domestic
animals, or pets. See MINN. STAT. § 97B.671, subdiv. 4(b).
The control area may be opened for 30 to 214 days, depending
on the time of year, and may be opened anytime within five
years of a verified loss. See id.; J.A. 439. Only trained and
certified predator controllers, operating with the permission of
the landowners within the control area, may legally take a wolf.
See MINN. STAT. § 97B.671, subdivs. 1, 4(b). In addition, a
person may shoot a wolf on land owned, leased, or managed by
that person at any time to protect that person’s livestock,
domestic animals, or pets, regardless of whether the wolf is an
immediate threat. See id. § 97B.645, subdiv. 8.

    Given those limitations, we disagree with the district
court’s and the Humane Society’s characterization of Zone B
as an “unregulated killing zone.” See Humane Society, 76 F.
Supp. 3d at 134; Humane Society’s Br. 77–78. Minnesota only
permits the killing of a wolf in Zone B by a limited class of
persons, and only after there has been some threat to livestock
or domestic animals. And at the time the 2011 Rule issued,
                               46
killing a wolf outside of the plan’s specific authorizations or
without a license was a gross misdemeanor. See MINN. STAT.
§ 97A.331, subdiv. 7 (2011), repealed by Act of May 3, 2012,
ch. 277, art. 1, § 91, 2012 Minn. Laws 1169.

      In other words, the Minnesota Plan does not authorize the
unregulated killing of any wolf at any time by any person. It
provides for regulated killing. To be sure, killings are allowed
at higher numbers than the Humane Society wants. That does
not make the Service’s decision unreasoned or arbitrary and
capricious, however. To the contrary, the Service adequately
explained why Minnesota’s new depredation scheme was
unlikely to threaten the wolves’ survival. In coming to that
conclusion, the Service did not ignore that the wolves residing
in Zone B “could be subject to substantial reduction in
numbers, and at the extreme, wolves could be eliminated from
Zone B.” 2011 Rule, 76 Fed. Reg. at 81,704. Rather, the
Service explained that “there is no way to reasonably evaluate
in advance the extent to which residents of Zone B will use this
new authority, nor how vulnerable Zone B wolves will be” in
actuality. Id. What the Service did know and found relevant
to its decision was that statistical data from 2007 to 2008, when
the Minnesota gray wolves were not federally listed, revealed
that only six wolves were shot in Zone B during that time
period, and in 2009 only one additional wolf was taken. Id.
Overall, the total number of wolves taken through depredation
controls from 2007 to 2008 (133 in 2007, 143 in 2008) was
comparable to the number that had been taken under a prior
federal regulation. See id. (under pre-2007 federal regulation,
105 wolves were killed in 2004, 134 in 2005, and 122 in 2006).

     Looking to data from 2007 to 2008 to predict the
consequences of delisting was entirely reasonable because
there was an absence of federal regulation and a presence of
state depredation authorizations nearly identical to the regime
                                47
that would operate after delisting. In addition, the Service is
obligated to continue monitoring the gray wolf for five years
following any successful delisting and to make “prompt use”
of its emergency powers “to prevent a significant risk to the
well being of any such recovered species.” 16 U.S.C.
§ 1533(g)(2). Concerned entities also remain free to petition
the Service to relist the gray wolf should it be threatened once
more. Id. § 1533(b)(3). For those reasons, the Service’s
consideration of the Minnesota plan in its delisting decision
was not arbitrary or capricious and was reasonably grounded in
substantial evidence.

                                2

     The Service’s decision to delist notwithstanding the lack
of state plans in North and South Dakota, Illinois, Iowa, Ohio,
and Indiana also did not rise to the level of arbitrary-and-
capricious decisionmaking, given the near non-existence of
gray wolves within those jurisdictions. The boundaries of the
Western Great Lakes segment includes only portions, at times
very small ones, of those six States, and few if any gray wolves
are found there. See, e.g., 2011 Rule, 76 Fed. Reg. at 81,671
(map of Great Lakes segment area); id. at 81,700 (sixteen total
reports of wolf sightings or deaths in North Dakota from 1999
to 2003); id. at 81,713 (no gray wolves found in Ohio and
Indiana). Scientific literature cited by the Service indicates that
the only gray wolves found in North and South Dakota are
primarily loners, not packs or mates with pups. Id. at 81,679;
see also id. at 81,700 (detailing every report of wolves in North
and South Dakota). Since 1993, there have been only five
verified wolf deaths from depredation and eight total deaths
from all causes of mortality in North and South Dakota. Id. at
81,713 (depredation deaths); id. at 81,700 (total deaths). Both
Ohio and Indiana list the gray wolf as “extirpated” from their
States. Id. at 81,713. Indiana, Illinois, Ohio, and Iowa, “do not
                               48
contain suitable habitat [for gray wolves] or currently
established packs[.]” Id.

      In addition, the absence of formal state wolf plans does not
mean that the few wolves in those States lack legal protection.
The Service explained that, in North Dakota and Iowa, there is
no open season on wolves because they are “furbearers.” 2011
Rule, 76 Fed. Reg. at 81,713. Illinois includes gray wolves on
its state endangered species list, making it illegal to possess or
kill a wolf in the state. Id.; see 520 ILL. COMP. STAT. 10/3
(detailing state law protections for endangered species). In
South Dakota, wolves are not listed as a game animal open for
hunting. 2011 Rule, 76 Fed. Reg. at 81,713. In short, in North
Dakota, South Dakota, Iowa, and Illinois, gray wolves are
protected from indiscriminate hunting. Only in Indiana and
Ohio, where wolves no longer exist, are there no formal
protections in place. Id. But it is not arbitrary or capricious to
overlook a State’s failure to protect an animal that does not
exist within its borders.

     Further, for all six of the States with no wolf plans, the
Service reasonably concluded that the deaths of any wolves
that might enter those States would be so minimal as to pose no
threat to the segment’s survival. 2011 Rule, 76 Fed. Reg. at
81,713. For example, the deaths since 1993 of a total of eight
wolves in North and South Dakota is quite unlikely to pose a
survival threat to the several thousand wolves protected within
Minnesota’s borders. Similarly, the death of a lone wolf that
might roam into Indiana or Ohio would be highly unlikely to
affect the health or sustainability of the Western Great Lakes
segment.

    The district court faulted the Service’s decision on the
ground that the limited number of wolves “does not foreclose
the possibility of an increased presence there[.]” Humane
                              49
Society, 76 F. Supp. 3d at 134. True. But the Endangered
Species Act tasks the Service with determining whether the
species is endangered or threatened, not whether the species
could reach still higher population levels if given more
protection. Challenges to expanding a species’ territory do not
by themselves undermine survival in existing territory.

     We accordingly hold that the absence of conservation
plans for the gray wolves in North Dakota, South Dakota,
Illinois, Iowa, Ohio, and Indiana does not render the Service’s
decision to delist the Western Great Lakes gray wolves
arbitrary and capricious on this record.

                               C

     Finally, the Humane Society challenges the 2011 Rule as
violating the Service’s statutory obligation to ground the
delisting decision in the best available science, 16 U.S.C.
§ 1533(b)(1)(A). The Humane Society argues first that science
does not support the 2011 Rule because the Service admits that
the Minnesota gray wolf is not a separate species of wolf under
the Endangered Species Act. The Humane Society argues
secondly that the 2011 Rule responded to political pressure, not
science. Neither argument succeeds.

                               1

     With respect to the status of the gray wolf in Minnesota,
the Service initially proposed classifying it as a separate
species (the “eastern wolf” or Canis lycaon). See Proposed
Rule to Revise the List of Endangered and Threatened Wildlife
for the Gray Wolf (Canis lupus), 76 Fed. Reg. 26,086, 20,086
(May 5, 2011) (“Proposed 2011 Rule”). But in the final 2011
Rule, the Service admitted that “neither a scientific consensus
nor the majority opinion of researchers on the taxonomy of
wolves” supported designating the wolves in Minnesota as a
                              50
distinct species. 2011 Rule, 76 Fed. Reg. at 81,669. In the
Humane Society’s view, once the Service determined that the
Minnesota gray wolf was not a separate species, the Service
should have withdrawn the rule, rather than promulgate a final
rule “without knowing the species that it is both listing and
delisting.” Humane Society’s Br. 61 (emphasis in original).

     But the Service did know that the Minnesota wolves that
it added to the Western Great Lakes segment were part of the
gray wolf species. See 2011 Rule, 76 Fed. Reg. at 81,669 (“The
wolves that occupy the [Western Great Lakes segment] have
long been accepted as gray wolves, C. lupus[.]”). In that
respect then, the Service’s treatment of the wolves in
Minnesota as part of the gray wolf species aligns with the best
science available, which was inconclusive as to whether the
Minnesota wolves were a separate species or just a subspecies
of the gray wolf. See id. at 81,668–81,669 (discussing the
scientific literature on wolf taxonomy).

     In any event, the Service’s recognition of the Western
Great Lakes segment did not depend on a finding that the
Minnesota wolves were a separate species. From the outset,
the Service proposed recognizing a distinct population segment
in the region. See Proposed 2011 Rule, 76 Fed. Reg. at 26,094
(“Within this rule we are proposing changes to the listing for
C. lupus and are initiating a status review for C. lycaon. These
two actions combined will address all wolves in the [Western
Great Lakes] region.”); id. (“Our proposed action here is to
establish the existence of a [Western Great Lakes] distinct
population segment of C. lupus and to determine that the
[segment] is neither endangered nor threatened, despite its
proximity to a closely related species, C. lycaon—a species
whose status we will evaluate for possible protection under the
Act in the near future.”). When the science did not support
according a distinct species status to wolves in Minnesota, the
                              51
Service followed where the science led by treating the
Minnesota wolves as non-distinct and grouping them with all
of the other wolves in the Western Great Lakes region.

                               2

     The record likewise does not support the Humane
Society’s charge that the delisting decision was driven by
politics rather than science. The Society’s argument relies
primarily on a single letter from United States Senator Amy
Klobuchar of Minnesota supporting delisting, which prompted
several emails within the Service discussing the Senator’s
letter.     But a single communication from an elected
representative conveying the views of constituents could not by
itself politically poison an agency’s decisionmaking. That is
especially true when, as here, the Society does not point to any
science that the Service ignored, misused, or manipulated, or
to any material switch in the Service’s position after receiving
the letter.

     On December 7, 2010, Senator Klobuchar sent a letter to
Ken Salazar, the then-Secretary of the Interior, “urg[ing]” the
Service “to expedite the delisting of the gray wolf in the Great
Lakes” and communicating her intent to introduce legislation
“to help speed-up this process.” J.A. 771. Assistant Secretary
Thomas Strickland’s response to Senator Klobuchar referenced
the 2009 Rule delisting the gray wolf in that region, which at
that time had been withdrawn due to litigation, and further
informed the Senator that the Service intended to publish a new
proposed rule delisting the wolf by April 2011. Senator
Klobuchar then made a public announcement about the
Service’s forthcoming proposed rule.

    Such a commonplace senatorial inquiry, standing alone,
cannot taint an agency decision that is otherwise adequately
reasoned and grounded in the factual record. And certainly not
                                52
here where the Service’s threefold effort to delist the region’s
gray wolves preceded the Senator’s letter by multiple years.
See 2003 Rule, 68 Fed. Reg. at 15,857 (final rule delisting gray
wolves); 2007 Rule, 72 Fed. Reg. at 6,101 (same); 2009 Rule,
74 Fed. Reg. at 15,120 (same). In addition, the Service had
received multiple petitions to delist the Western Great Lakes
wolves and had decided that those petitions presented
substantial evidence meriting delisting several months before
Senator Klobuchar’s letter. See 90-Day Finding on Petitions to
Delist the Gray Wolf in Minnesota, Wisconsin, Michigan and
the Western Great Lakes, 75 Fed. Reg. 55,730, 55,735 (Sept.
14, 2010).

      The Humane Society’s reliance on Save Our Springs v.
Babbitt, 27 F. Supp. 2d 739 (W.D. Tex. 1997), actually proves
the opposite. Unlike the case at hand, the Service in Save Our
Springs succumbed to political pressure and withdrew a
proposed listing of salamanders even though it had earlier
stated that the salamander was the “top priority in the region
for listing.” Id. at 745. The level of political pressure,
moreover, bears no resemblance to the single letter in this case.
In Save Our Springs, the pressure came through a letter from
the Governor of Texas, emails from employees worrying that
listing was a “hot” issue and noting “intense opposition” to the
proposal from all levels of Texas government, and “inferences
that political lobbyists for the development community worked
with political appointees.” Id. The record here reflects no such
concerted pressure, no manipulation or disregard of material
evidence, and no change in the Service’s course of action
before and after the single communication. 10


    10
        Likewise, Western Watersheds Project v. Fish & Wildlife
Service, 535 F. Supp. 2d 1173 (D. Idaho 2007), involved a “well-
documented history” of a Deputy Assistant Secretary “intervening in
the listing process,” “editing scientific conclusions” and
                                  53
     We accordingly find no merit to the charge of improper
political influence in this case.

                                  V

     A common remedy when we find a rule is invalid is to
vacate. See Sugar Cane Growers Co-op. of Fla. v. Veneman,
289 F.3d 89, 97 (D.C. Cir. 2002) (“Normally when an Agency
* * * clearly violates the APA we would vacate its action[.]”).
But we may remand without vacatur depending upon “the
seriousness of the order’s deficiencies (and thus the extent of
doubt whether the agency chose correctly) and the disruptive
consequences of [vacating the Rule,] an interim change that
may itself be changed.” Id. at 98 (citation omitted); Allina
Health Servs. v. Sebelius, 746 F.3d 1102, 1110 (D.C. Cir.
2014); see also United States Sugar Corp. v. EPA, 844 F.3d
268, 270 (D.C. Cir. 2016) (per curiam) (“Although remand
without vacatur may in some circumstances invite prejudicial
agency delay, in other circumstances vacatur itself carries
more-harmful consequences. We have therefore frequently
remanded without vacating when a rule’s defects are curable
and where vacatur would at least temporarily defeat * * * the
enhanced protection of the [rule].”) (first alteration in original;
internal quotation marks and citations omitted).

      In this case, the agency’s analysis (i) wholly failed to
address the effect on the remnant population of carving out the
Western Great Lakes segment, and in doing so (ii) misapplied
the Service’s own discreteness and significance tests, and also
(iii) turned its back on the implications of historical range loss.
Those are major shortcomings that go to the heart of the

“intimidating [Service] staffers,” id. at 1175; see also id. at 1188
(The Deputy Assistant Secretary “had extensive involvement in the
sage-grouse listing decision, used her intimidation tactics in this
case, and altered the ‘best science’ to fit a not-warranted decision.”).
                              54
Service’s delisting decision. Given the serious and pervading
role those deficiencies played in the agency’s decisionmaking,
there is substantial “doubt whether the [Service] chose
correctly” in promulgating the 2011 Rule, Sugar Cane
Growers, 289 F.3d at 98 (citation omitted). That makes vacatur
appropriate. See id. at 97–98; Fox Television Stations, Inc. v.
FCC, 280 F.3d 1027, 1049, 1052–1053 (D.C. Cir. 2002).

     In addition, vacatur would not trigger disruptive
consequences. The agency has failed repeatedly over the last
sixteen years to make a delisting decision that complies with
the APA, and it has not shown that vacatur here would be any
more disruptive than it was on the Service’s last three failed
occasions. With respect to protecting domestic animals in the
interim, federal regulations already permit depredation control
in Minnesota, which is where most of the gray wolves in the
Western Great Lakes segment live. See 50 C.F.R. § 17.40(d).

     Because of the “seriousness of the [Rule’s] deficiencies”
and the absence of materially “disruptive consequences,” we
affirm the judgment of the district court vacating the Service’s
2011 Rule.

                                                    So ordered.
