The Gray Wolf Under the Endangered Species Act (ESA): A Case Study in Listing and Delisting Challenges

January 17, 2020 – November 25, 2020 R46184

The Gray Wolf Under the Endangered Species
November 25, 2020
Act (ESA): A Case Study in Listing and Delisting Erin H. Ward
Challenges
Legislative Attorney

Under the Endangered Species Act of 1973 (ESA or the Act; 16 U.S.C. §§ 1531-1544), the U.S.
Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS) (together,

the Services) determine which species to “list” as “endangered species” or “threatened species,”
terms defined in the Act. Species, subspecies, and distinct population segments (DPSs) may all be listed as “species” under
the Act. Listing a species invokes certain protections under the Act and a requirement that the Services develop a recovery
plan to conserve the species. A species listed as threatened may be reclassified as endangered or vice versa. The Services may
also remove a species from the list, often called delisting, if the species no longer meets the definition of an endangered or
threatened species. The Services list, reclassify, and delist species through the agency rulemaking process, guided by
statutory criteria and definitions. Persons may—and often do—challenge the legality of those final rules through litigation.
When such challenges succeed, the court remands the rule to the applicable Service for further proceedings and may vacate
the challenged rule.
The case of the gray wolf (Canis lupus) exemplifies the legal issues that arise with listing and delisting species as threatened
and endangered under the ESA and how FWS has addressed them. FWS first listed the gray wolf as endangered in 1967
under the Endangered Species Preservation Act (ESPA), a predecessor of the ESA. The gray wolf’s status and regulation
under the ESA and its predecessors have been the subjects of numerous FWS rules and court opinions. FWS’s gray wolf
rules show how the agency’s approach to interpreting and implementing the ESA has evolved and highlight hurdles that may
arise with species’ status determinations.
As American pioneers settled the West, hunting and other human-caused mortality, spurred by federal and state bounties,
brought the gray wolf to near extinction. By the 1960s, the only population remaining in the lower 48 states was in the
northern Minnesota forests. FWS listed the eastern timber wolf (C. lupus lycaon, a gray wolf subspecies found in Minnesota)
as endangered under the ESPA. By 1976, three more gray wolf subspecies—the Mexican wolf (C. lupus baileyi), the northern
Rocky Mountain wolf (C. lupus irremotus), and the Texas wolf (C. lupus monstrabilis)—were listed as endangered under the
ESA. In 1978, FWS combined all gray wolf subspecies listings. One rule listed the entire gray wolf species as endangered in
the lower 48 states except Minnesota, and a separate rule listed the gray wolf in Minnesota as threatened. In the next few
years, FWS created subspecies recovery plans that outlined management strategies and recovery criteria. In the 1990s, FWS
reintroduced gray wolves to the northern Rocky Mountains and the Southwest as experimental populations under the ESA.
Protected under the ESA from human-caused mortality, which FWS identified as the greatest threat to the species, gray wolf
populations increased. In the 2000s, FWS tried on multiple occasions to reclassify or delist gray wolf DPSs it had determined
were no longer in risk of extinction, but courts vacated many of the agency’s rules. In 2015, FWS listed the Mexican wolf
separately as endangered. In that rule, FWS adjusted the territory over which the gray wolf in the lower 48 states was
endangered or threatened to exclude the Mexican wolf’s territory in Arizona and New Mexico. On November 3, 2020, FWS
published a final rule delisting the gray wolf in the lower 48 states, with an effective date of January 4, 2021. This delisting
rule does not affect the separate listing for the Mexican wolf as endangered.
FWS’s efforts to recover the gray wolf under the ESA exemplify the regulatory and legal challenges that arise when listing
and delisting species under the Act. From initial listing to recovery and reintroduction efforts to more recent attempts to delist
the gray wolf, FWS has addressed such issues as uncertainties in gray wolf taxonomy, ambiguous statutory terms (e.g.,
“foreseeable future” and “significant portion of its range”), and the adequacy of state management plans. Stakeholders have
questioned FWS’s choices in comments to the proposed rules and have challenged many of the agency’s gray wolf rules in
court. Many of the legal challenges to FWS’s delisting rules have succeeded, with courts vacating the rules and remanding
them to the agency. The history of FWS’s regulation of the gray wolf under the ESA and related litigation serve as a useful
case study in how regulatory and legal challenges have shaped FWS’s interpretation and application of key terms when
listing and delisting species under the Act.
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Appendixes
Appendix. Timeline ....................................................................................................... 42

Contacts
Author Information ....................................................................................................... 45

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nder the Endangered Species Act of 1973 (ESA or the Act),1 the U.S. Fish and Wildlife
Service (FWS) and the National Marine Fisheries Service (together, the Services)
U determine which species to “list” as “endangered species” or “threatened species,” terms
defined in the Act.2 Species, subspecies, and distinct population segments (DPSs) may al be
listed as “species” under the Act.3 Listing a species invokes certain protections under the Act and
a requirement that the Services develop a recovery plan to conserve the species.4 A species listed
as threatened may be reclassified as endangered or vice versa.5 The Services may also remove a
species from the list, often cal ed delisting,6 if the species no longer meets the definition of an
endangered or threatened species.7 The Services list, reclassify, and delist species through the
agency rulemaking process, guided by statutory criteria and definitions.8 Persons may—and often
do—chal enge the legality of those final rules through litigation.9 When such chal enges succeed,
the court remands the rule to the applicable Service for further proceedings and may vacate the
chal enged rule.10
The gray wolf (Canis lupus) presents a useful example of the legal issues that arise with listing
and delisting species as threatened and endangered under the ESA and how FWS has addressed
those issues. The gray wolf was among the first species identified by federal law as endangered
after being hunted to near extinction in the lower 48 states.11 FWS has issued numerous rules in
connection with its efforts to recover the gray wolf under the ESA.12 Many of those rules have
been chal enged in court, and a number of them have been vacated and remanded to FWS.13 FWS
has addressed issues such as uncertainties in gray wolf taxonomy, ambiguous statutory terms
(e.g., “foreseeable future” and “significant portion of its range”), and the adequacy of state
management plans. This report uses FWS’s regulation of the gray wolf under the ESA and related
litigation as a case study in how legal chal enges have shaped FWS’s interpretation of ESA
provisions when listing and delisting species under the Act. The report begins by laying out
general legal principles governing agency rulemaking under the ESA before reviewing the history
of FWS’s actions to list, recover, and delist the gray wolf and subsequent litigation. The report
then uses this regulatory and litigation history to analyze specific issues that arise when listing
and delisting species under the Act.

1 Pub. L. No. 93-205, 87 Stat. 884 (1973) (codified at 16 U.S.C. §§ 1531 – 1544).
2 16 U.S.C. § 1533.
3 Id. §§ 1532(16) & 1533(a).
4 Id. §§ 1533(f), 1536, & 1538. T he Secretary of the Interior or of Commerce, as applicable, may decline to develop
and implement a recovery plan only upon finding “that such a plan will not promote the conservation of the species.”
Id. § 1533(f)(1).
5 Id. § 1533(a) & (c).
6 T hough the term “delist” does not appear in the Endangered Species Act of 1973 (ESA or the Act), it is generally
used by the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Services (together, the Services)
to refer to removing a species from the list of endangered or threatened species.
7 Id.
8 Id. § 1533(a); 5 U.S.C. § 553.
9 See, e.g., Defenders of Wildlife v. Sec’y, U.S. Dep’t of the Interior, 354 F. Supp. 2d 1156 (D. Ore. 2005); Nat’l
Wildlife Fed’n v. Norton, 386 F. Supp. 2d 553 (D. Vt. 2005).
10 See, e.g., Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp. 2d 7, 21 (D.D.C. 2008).
11 Endangered Species, 32 Fed. Reg. 4001, 4001 (Mar. 11, 1967).
12 See infra “History of Listing and Delisting the Gray Wolf” section.
13 Id.
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Listing and Delisting Species Under the Endangered
Species Act
The ESA aims to accomplish its goal of conserving fish, wildlife, and plants species threatened
with extinction by “listing” species the Services determine to be endangered or threatened.14 The
ESA’s provisions and protections general y apply only to these listed species.15 The Act’s legal
framework determines when and how species are listed, reclassified,16 and delisted.17 The
Secretary of the Interior and the Secretary of Commerce (this report refers to “the Secretary” to
mean either the Secretary of the Interior or the Secretary of Commerce, as applicable) review
species’ statuses under the Act on the respective Secretary’s own initiative or in response to
petitions.18 Any person19 may petition the Secretary to list, reclassify, or delist a species.20 The
ESA prescribes when and how the Secretary is required to respond to such petitions, as shown in
Figure 1.

14 16 U.S.C. §§ 1531(b), 1533(a) & (c).
15 Candidate species being considered for listing receive some minimal protections under the Act before they are listed.
50 C.F.R. § 424.02.
16 Reclassification, as used in this report, refers to a “change[] in status” from endangered to threatened or from
threatened to endangered. See 16 U.S.C. § 1533(c)(2)(B).
17 See generally id. § 1533.
18 Id. § 1533(b).
19 Under the ESA, “ person” is defined to mean “ an individual, corporation, partnership, trust, association, or any other
private entity; or any officer, employee, agent, department, or instrumentality of the Federal Government, of any State,
municipality, or political subdivision of a State, or of any foreign government; any State, municipality, or political
subdivision of a State; or any other entity subject to the jurisdiction of the United States. ” Id. § 1532(13).
20 Id. § 1533(b)(3); 5 U.S.C. § 553(e).
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The Gray Wolf: A Case Study in Endangered Species Act Listing Challenges

Figure 1. Petitioning the Secretary Under the Endangered Species Act

Source: Congressional Research Service (based on 16 U.S.C. § 1533(b)).
Note: “The Secretary” refers to the Secretary of the Interior or the Secretary of Commerce, as applicable.
A status review, conducted pursuant to a petition that may be warranted or at the Secretary’s
initiative, determines whether a species should be or remain listed.21 Figure 2 depicts the general
pathway for a species from status review and listing through post-delisting monitoring and
management under the ESA framework. A brief explanation of each stage is provided below
Figure 2.22

21 16 U.S.C. § 1533(a) & (b)(3)(A). For species listed as endangered or threatened, a status review could determine that
the species should be reclassified from endangered to threatened or vice versa, as applicable. Id. § 1533(c).
22 For more information on the ESA, see CRS Report RL31654, The Endangered Species Act: A Primer, by Pervaze A.
Sheikh and CRS In Focus IF11241, The Legal Fram ework of the Endangered Species Act (ESA) , by Erin H. Ward.
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The Gray Wolf: A Case Study in Endangered Species Act Listing Challenges

Figure 2. Listing and Delisting Species Under the Endangered Species Act

Source: Congressional Research Service (based on 16 U.S.C. §§ 1532, 1533, 1536 & 1538).
Note: “Secretary” refers to either the Secretary of the Interior or the Secretary of Commerce, as applicable.
Listing. As a threshold matter, the Secretary may list only groups of organisms that qualify as a
“species” under the ESA,23 defined to include subspecies and DPSs.24 Because the term “species”
under the Act has a distinct legal meaning that may differ from its conventional or taxonomic
meaning,25 this report uses the term “species” to refer to species as defined by the Act (i.e.,
including subspecies and DPSs) and the term “full species” when referring to a taxonomic

23 16 U.S.C. § 1532(16).
24 Distinct population segments (DPSs) are limited to species of vertebrate fish or wildlife that interbreed when mature.
16 U.S.C. § 1532(16). For more information about how the Services have interpreted and applied this term, see infra
“Designating Distinct Population Segments (DPSs)
25 See, e.g., John L. Gittleman, Species, ENCYCLOPAEDIA BRITANNICA (Nov. 6, 2019),
https://www.britannica.com/science/species-taxon.
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species. For species eligible for listing, the Secretary examines whether the species qualifies as an
endangered species or threatened species, as defined by the Act,26 because of any of the five
factors listed in Figure 2. The ESA requires the Secretary to make this determination “solely”
based on the “best scientific and commercial data available.”27 Based on this evaluation, the
Secretary either lists the species as endangered or threatened, as appropriate, or determines the
species is ineligible for listing and, if the Secretary conducted the status review pursuant to a
petition to list, denies the petition.28 The Secretary may also determine that a species qualifies as
an endangered or threatened species but that the species cannot be listed at the time due to the
Services’ priorities and limited resources. In that case, the Secretary may deny a petition as
warranted but precluded.29 The Secretary publishes listing determinations in the Federal Register
and the Code of Federal Regulations.30
Listed. Once endangered and threatened species are listed, the ESA directs federal agencies to
“conserve” them and their ecosystems.31 As shown in Figure 2, the Act provides two types of
mechanisms to conserve listed species and facilitate their recovery.32 First, as shown in the
Protections box of Figure 2, it protects the species by prohibiting certain acts with respect to
endangered species; similar prohibitions may also be extended to threatened species.33 The Act
further protects listed species by requiring federal agencies to consult with the Services when
their actions, or actions they approve or fund, could affect listed species—often cal ed Section 7
consultations.34 Through this process, federal agencies assess the potential effects of their actions
on any endangered or threatened species and evaluate, as necessary, alternatives that would
mitigate the impact.35
Second, as shown in the Recovery Tools box in Figure 2, the ESA provides tools to facilitate the
recovery of the species. The Act general y requires the Secretary to develop and implement a

26 16 U.S.C. § 1532(6) & (20).
27 Id. § 1533(b). “Best scientific and commercial data” is not defined in the ESA.
28 Id. § 1533(a)-(c).
29 Id. § (b)(3)(B)(iii).
30 Id. § 1533(c)(1); 50 C.F.R. § 17.11-17.12. T he Secretary is also required, “to the maximum extent prudent and
determinable,” to designate critical habitat concurrently with listing a species. 16 U.S.C. § 1533(a)(3)(A). Critical
habitat designations are also published in the Federal Register and Code of Federal Regulations. Id. § 1533(c)(1); 50
C.F.R. § 17.95.
31 16 U.S.C. § 1531(b). Conserving an endangered or threatened species means the federal agency uses “all methods
and procedures which are necessary to bring [the species] to the point at which the measures provided [in the ESA] are
no longer necessary.” Id. § 1532(3).
32 T he Services use the term “ recovery” to mean “improvement in the status of listed species to the point at which
listing is no longer appropriate under the criteria set out in section 4(a)(1) of the Act.” 50 C.F.R. § 402.02. See also
Endangered and T hreatened Wildlife and Plants; Final Rule to Reclassify and Remove the Gray Wolf from the List of
Endangered and T hreatened Wildlife in Portions of the Conterminous United States; Establishment of T wo Special
Regulations for T hreatened Gray Wolves, 68 Fed. Reg. 15,804, 15,809 (Apr. 1, 2003) (“Essentially, recover and
conserve both mean to bring a species to the point at which it no longer needs th e protections of the Act, because the
species is no longer threatened or endangered.”).
33 16 U.S.C. § 1538(a) & 1533(d). T he Act requires the Secretary to issue regulations, often called 4(d) rules, for
threatened species “as he deems necessary and advisable to provide for the conservation of such species.” Id.
§ 1533(d). In those regulations, the Secretary may prohibit any act that is prohibited with respect to endangered species,
with minor limitations. Id.
34 Id. § 1536(a)(2). T his consultation, often called a Section 7 consultation, is intended to ensure that federal agency
actions are “not likely to jeopardize the continued existence of endangered or threatened species” or to “adversely
modify” or to destroy critical habitat. Id. § 1536; 50 C.F.R. Part 402.
35 16 U.S.C. § 1536; 50 C.F.R. Part 402.
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recovery plan for each listed species unless such a plan would “not promote the conservation of
the species.”36 The recovery plan includes any site-specific management actions needed to
conserve the species, objective and measureable criteria that would merit delisting the species if
met,37 and estimates of timelines and costs.38 In addition to recovery plans, Congress amended the
ESA in 1982 to al ow the Services to reintroduce experimental populations of listed species,
which are regulated as threatened species regardless of the listed species’ status.39 Experimental
populations must be “wholly separate geographical y” from existing natural populations of the
species.40
As shown in the Review Status box in Figure 2, the Secretary must review the status of a listed
species every five years41—or pursuant to a petition to reclassify or delist the species that may be
warranted42—to determine whether it stil qualifies as an endangered or threatened species.
Species are reclassified or delisted based on the same criteria used to list species, as shown in the
Status box in Figure 2.43
Post-delisting. Once a species is delisted, the states in which the species resides resume control
over management of the recovered species.44 The Secretary and the states monitor the status of a
recovered species for at least five years after delisting.45 In this period, if the Secretary determines
that there is a significant risk to the wel -being of the species, the Secretary must exercise
emergency powers to restore the Act’s protections to the species for 240 days, during which time
the Secretary may begin rulemaking proceedings to relist the species.46
Administrative Law and Statutory Interpretation
The Services list, reclassify, and delist species through the rulemaking process. The principles of
administrative law and statutory interpretation that general y govern the agency rulemaking
process and judicial review underpin the Services’ actions under the ESA.47 Agencies use rules,

36 16 U.S.C. § 1533(f).
37 Species are not automatically delisted if they meet the objective, measurable criteria in their recovery plans. T he
Secretary must undertake agency rulemaking to delist the species in accordance with the ESA listing criteria, 5 U.S.C.
§ 553; 16 U.S.C. § 1533(a), and circumstances may have changed since the criteria were set.
38 16 U.S.C. § 1533(f). For example, the recovery plan may specify the number of breeding p airs that must be sustained
for a certain number of years in a particular geographic area to consider the species recovered. See, e.g., Northern
Rocky Mountain Wolf Recovery Plan, U.S. FISH & WILDLIFE SERV., at v (1987).
39 Endangered Species Act Amendments, Pub. L. No. 97-304, 96 Stat. 1411 (1982) (codified at 16 U.S.C. § 1539(j));
16 U.S.C. § 1539(j)(2)(C). A court, reviewing relevant legislative history, concluded that Congress added this option,
with its greater regulatory flexibility, to address the Services’ frustration with political opposition to such reintroduction
efforts borne from “industry’s fears experimental populations would halt development projects.” Wyo. Farm Bureau
Fed’n v. Babbitt, 199 F.3d 1224, 1231-32 (10th Cir. 2000) (citing H.R. Rep. No. 97-567, at 8 (1982)).
40 16 U.S.C. § 1539(j)(1).
41 Id. § 1533(c)(2)(A).
42 Id. § 1533(b).
43 Id. § 1533(c).
44 T he Secretary generally reviews and may need to approve state management plans for states where a recovered
species is found as part of the recovery criteria and five-factor threats assessment before finalizing the delisting rule.
See, e.g., Endangered and T hreatened Wildlife and Plants; Final Rule Designating the Northern Rocky Mountain
Population of Gray Wolf as a Distinct Population Segment and Removing this Distinct Population Segment from the
Federal List of Endangered and T hreatened Wildlife, 73 Fed. Reg. 10,514, 10,546-52 (Feb. 27, 2008).
45 16 U.S.C. § 1533(g)(1).
46 Id. §§ 1533(b)(7) & (g)(2).
47 For in-depth information on agency rulemaking, judicial review, and statutory interpretation, see CRS Report
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among other tools, to implement and interpret statutes and promulgate regulations.48 The
Administrative Procedure Act (APA)49 general y governs agency rulemaking by prescribing
procedural requirements for agencies to follow and providing an opportunity for judicial review
of final agency actions.50 The APA requires agencies to publish a proposed rule to provide notice
of the agency’s proposed action and provide an opportunity for public comment, then to publish a
final rule that concisely states the agency’s basis and purpose for the rule.51 The agency’s
statement must general y address significant comments and explain the agency’s rationale for
those comments not incorporated into the final rule.52 Any changes in the final rule must be a
“logical outgrowth” of the proposed rule to comport with due process.53
Parties affected by an agency rule can general y seek judicial review of the agency’s action.54 To
the extent the rule relies on an agency’s interpretation of a provision in a statute it administers, the
court general y evaluates the agency’s interpretation under the Chevron doctrine.55 Under the
Chevron doctrine,56 the court first determines whether the statutory provision is ambiguous (i.e.,
if there are multiple permissible meanings) by relying on principles of statutory interpretation.57
The court may look to the plain meaning of the term in common parlance, the provision’s
statutory context, how the term is used elsewhere in the statute or other statutes, the statute’s
purpose and legislative history, and whether a particular interpretation would render a term
superfluous, lead to absurd results, or raise constitutional questions.58 If the court determines that
a statutory provision is ambiguous, then it defers to the administering agency’s interpretation so
long as it is a permissible (i.e., reasonable) interpretation.59

R41546, A Brief Overview of Rulem aking and Judicial Review, by T odd Garvey, and CRS Report R45153, Statutory
Interpretation: Theories, Tools, and Trends, by Valerie C. Brannon.
48 5 U.S.C. § 551(4).
49 Id. §§ 551-559, 701-706.
50 Id.
51 Id. § 553. Congress may provide by statute that all or part of the Administrative Procedure Act (APA) does not apply
to certain agency actions. In some cases, Congress has provided alternative rulemaking procedures for an agency to
follow. See, e.g., 42 U.S.C. 7607(d) (prescribing rulemaking procedures for the U.S. Environmental Protection Agency
to follow for rules promulgated under certain provisions of the Clean Air Act).
52 See, e.g., Perez v. Mortg. Bankers Ass’n, 135 S. Ct. 1199, 1203 (2015).
53 Envt’l Integrity Project v. EPA, 425 F.3d 992, 996 (D.C. Cir. 2005) (“[A]n agency’s proposed rule and its final rule
may differ only insofar as the latter is a ‘logical outgrowth’ of the former.”). A final rule is a “logical out growth” of the
proposed rule if parties “‘should have anticipated’ that the change was possible, and thus reasonably should have filed
their comments on the subject during the notice-and-comment period.” Northeast Md. Waste Disposal Auth. v. EPA,
358 F.3d 936, 952 (D.C. Cir. 2004).
54 5 U.S.C. § 702. Judicial review is a right created by statute under the APA, but Congress may and has limited the
availability of judicial review for certain agency actions or entirely precluded judicial review. See, e.g., 38 U.S.C.
§ 511(a); 42 U.S.C. § 7607(b).
55 See, e.g., Adams Fruit Co. v. Barrett, 494 U.S. 638, 649 (1990).
56 Chevron U.S.A., Inc. v. Natural Res. Def. Council, 467 U.S. 837, 843 (1984). For more information on the Chevron
doctrine, see CRS Report R44954, Chevron Deference: A Prim er, by Valerie C. Brannon and Jared P. Cole.
57 Chevron U.S.A., Inc., 467 U.S. at 842.
58 See, e.g., NLRB v. SW Gen., Inc., 137 S. Ct. 929, 938-39 (2017); McDonnell v. United States, 136 S. Ct. 2355, 2369
(2016); Yates v. United States, 135 S. Ct. 1074, 1080 (2015) ; FAA v. Cooper, 566 U.S. 284, 291 -92 (2012); FCC v.
AT &T Inc., 562 U.S. 397, 407-08 (2011); Stenberg v. Carhart, 530 U.S. 914, 942 (2000); City of Chicago v. Envtl.
Def. Fund, 511 U.S. 328, 337-38 (1994); Anita S. Krishnakumar, Statutory Interpretation in the Roberts Court’s First
Era: An Em pirical and Doctrinal Analysis, 62 HASTINGS L.J. 221, 251 (2010).
59 Chevron U.S.A., Inc., 467 U.S. at 843.
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Under the APA, a court must set aside agency rules if it finds the rule is “arbitrary, capricious, an
abuse of discretion, or otherwise not in accordance with law.”60 For example, a court may
determine that a rule is arbitrary and capricious because the agency’s interpretation of an
ambiguous term is not a permissible one.61 A court may also hold that an agency rule is arbitrary
and capricious if it is il ogical y reasoned, fails to consider an important aspect of the problem, or
is unsupported by the administrative record.62 When a court overturns an agency rule, it general y
vacates the rule and remands it to the agency.63
History of Listing and Delisting the Gray Wolf
The gray wolf has a long history as a listed species under the ESA and its predecessors.
As discussed in this section, from the initial listing to the present, nearly every element of
the listing and delisting legal framework has been implicated in regulating the gray wolf
under the Act. (See “Listing and Delisting Species Under the Endangered Species Act”
section.) Table 1 includes a timeline of legislative, regulatory, and litigation actions by
population, and Table A-1 in the Appendix provides a more detailed version. The
substantive issues that have been raised in the various rulemakings and court opinions
described in this section are discussed by topic in the “Chal enges When Listing and
Delisting Species” section.

60 5 U.S.C. § 706(2)(A).
61 See, e.g., Defenders of Wildlife v. Salazar, 729 F. Supp. 2d 1207, 1224 -26 (D. Mont. 2010). Cf. Sec’y of Labor,
Mine Safety & Health Admin v. Nat’l Cement Co. of Cal., Inc., 494 F.3d 1066, 1074 -75 (D.C. Cir. 2007).
62 See, e.g., Ctr. for Biological Diversit y v. U.S. Bureau of Land Mgmt., 698 F.3d 1101, 1124 (9th Cir. 2012); Am.
Fed’n of Gov’t Emps., Local 2924 v. Fed. Labor Relations Auth., 470 F.3d 375, 380 (D.C. Cir. 2006); United States v.
Dierckman, 201 F.3d 915, 926 (7th Cir. 2000) (quoting Bagdonas v. Dep’t of the T reasury, 93 F.3d 422, 426 (7th Cir.
1996)); Allied-Signal, Inc. v. Nuclear Reg. Comm’n, 988 F.2d 146, 152 (D.C. Cir. 1993).
63 See, e.g., Humane Soc’y of U.S. v. Kempthorne, 579 F. Supp. 2d 7, 21 (D.D.C. 2008).
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The gray wolf’s traits and history inform much of FWS’s analysis of threats to the species and
pathways to recovery. Gray wolves are the largest member of the Canidae (i.e., dog) family.64
They are frequently found in packs and occupy defined territory, but lone gray wolves may leave
their packs to join another pack or wander alone.65 Gray wolves are effective and adaptive
predators who general y hunt large prey, such as moose, elk, caribou, bison, and deer; they also
eat smal er prey.66 Historical y, gray wolves ranged throughout most of North America, Europe,
and Asia.67 On the North American continent, gray wolves were once found from Canada and
Alaska to northern Mexico except for much of the southeastern United States (where the related
but distinct red wolf lived) and parts of southern California.68 The arrival of European settlers and
their expansion into the western frontier led to widespread persecution of wolves as a result of
fear, superstition, and perceived and real conflicts between wolves and humans, such as attacks
on humans, domestic animals, or livestock.69 Encouraged by federal, state, and local bounties,
settlers poisoned, trapped, and shot wolves until they were eliminated from more than 95% of
their historical range.70
Listing and Recovery Efforts
FWS listed the first gray wolf subspecies, the eastern timber wolf (C. lupus lycaon), as
endangered in 1967 under the Endangered Species Preservation Act of 1966 (ESPA).71 After the
Endangered Species Conservation Act of 1969 (ESCA)72 amended the ESPA, FWS listed the
northern Rocky Mountain wolf (C. lupus irremotus) as endangered in 1973.73 Under the ESPA
and the ESCA, the Services could list only species or subspecies that were endangered
worldwide.74 Enacted in 1973,75 the ESA al owed the Services to identify a species as endangered
or threatened in al or a significant part of its range.76 After the ESA was enacted, FWS listed two
more gray wolf subspecies—the Mexican wolf (C. lupus baileyi) and the Texas wolf (C. lupus
monstrabilis)—as endangered in 1976.77 In 1978, FWS combined these listings into one listing
for the gray wolf species as endangered throughout the lower 48 states except Minnesota and a
separate listing for the gray wolf in Minnesota as threatened.78

64 Endangered and T hreatened Wildlife and Plants; Proposal to Reclassify and Remove the Gray Wolf from the List of
Endangered and T hreatened Wildlife in Portions of the Conterminous United States; Proposal to Establish T hree
Special Regulations for T hreatened Gray Wolves, 65 Fed. Reg. 43 ,450, 43,451 (July 13, 2000).
65 Id.
66 Id.
67 Id.
68 Id.
69 Id.
70 Id.
71 32 Fed. Reg. 4001 (Mar. 11, 1967).
72 Pub. L. No. 91-135, 83 Stat. 273 (1969).
73 Amendments to Lists of Endangered Fish and Wildlife, 38 Fed. Reg. 14,678 (June 4, 1973).
74 Pub. L. No. 89-669, 80 Stat. 926 (1966); Pub. L. No. 91-135, 83 Stat. 273 (1969).
75 Pub. L. No. 93-205, 87 Stat. 884 (1973) (codified at 16 U.S.C. §§ 1531 – 1544).
76 16 U.S.C. § 1533(a).
77 Determination That T wo Species of Butterflies Are T hreatened Species and T wo Species of Mammals are
Endangered Species, 41 Fed. Reg. 17,736 (Apr. 28, 1976); Endangered Status for 159 T axa of Animals, 41 Fed. Reg.
24,064 (June 14, 1976).
78 Reclassification of the Gray Wolf in the United States and Mexico, with Determination of Critical Habitat in
Michigan and Minnesota, 42 Fed. Reg. 9607 (Mar. 9, 1978).
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Between 1978 and 1982, FWS created recovery plans for the eastern timber wolf, the northern
Rocky Mountain wolf, and the Mexican wolf that outlined management strategies and recovery
criteria.79 It later updated each of those plans.80 In the 1990s, FWS reintroduced gray wolves into
central Idaho and the greater Yel owstone area in the northern Rocky Mountains and the
Southwest.81 FWS designated each population as a nonessential experimental population,
meaning FWS determined the population is not essential to the conservation of the species.82
Protected from human-caused mortality, which FWS identified as the greatest threat to the
species, gray wolf populations in the western Great Lakes region, the northern Rocky Mountains,
and the Southwest increased and expanded their ranges.83
Designating Distinct Population Segments (DPSs)
Beginning in the early 2000s, FWS promulgated a series of rules that simultaneously designated
gray wolf DPSs, removing them from (or dividing up) the previously listed gray wolf entities, and
reclassified or delisted them—nearly al of which have been overturned by courts. As mentioned
above, the ESA defines species to include taxonomic species, subspecies, and DPSs.84 The term
DPS is distinct to the ESA, unlike species and subspecies, which are commonly used taxonomic
terms with scientific meanings.85 The term DPS is not defined in the ESA. The Services issued a
DPS policy (DPS Policy) in 1996 explaining how they would interpret and apply the term.86
Under the DPS Policy, the Services evaluate the population’s discreteness87 and significance88 to
determine if it qualifies as a DPS and, therefore, a listable species under the Act.89 FWS has used

79 Recovery Plan for the Eastern Timber Wolf, EASTERN T IMBER WOLF RECOVERY TEAM (1978); Northern Rocky
Mountain Wolf Recovery Plan, U.S. FISH & WILDLIFE SERV. (1980); Mexican Wolf Recovery Plan, U.S. FISH &
WILDLIFE SERV. (1982).
80 Northern Rocky Mountain Wolf Recovery Plan, U.S. FISH & WILDLIFE SERV. (1987); Recovery Plan for the Eastern
Tim ber Wolf, EASTERN T IMBER WOLF RECOVERY TEAM (Rev. 1992); Mexican Wolf Recovery Plan: First Revision, U.S.
FISH & WILDLIFE SERV. (2017).
81 Endangered and T hreatened Wildlife and Plants; Establishment of a Nonessential Experimental Population of Gray
Wolves in Yellowstone National Park in Wyoming, Idaho, and Montana, 59 Fed. Reg. 60,252, 60,252 (Nov. 22, 1994);
Endangered and T hreatened Wildlife and Plants; Establishment of a Nonessential Experimental Population of Gray
Wolves in Central Idaho and Southwestern Montana, 59 Fed. Reg. 60,266, 60,266 (Nov. 22, 1994); Endangered and
T hreatened Wildlife and Plants; Establishment of a Nonessential Experimental Population of the Mexican Gray Wolf in
Arizona and New Mexico, 63 Fed. Reg. 1752, 1752 (Jan. 12, 1998).
82 59 Fed. Reg. at 60,252; 59 Fed. Reg. at 60,266; 63 Fed. Reg. at 1752.
83 See, e.g., Endangered and T hreatened Wildlife and Plants; Final Rule Designating the Western Great Lakes
Populations of Gray Wolves as a Distinct Population Segment; Removing the West ern Great Lakes Distinct Population
Segment of the Gray Wolf from the List of Endangered and T hreatened Wildlife, 72 Fed. Reg. 6052, 6053 -56 (Feb. 8,
2007); 73 Fed. Reg. 10,514, 10523 -26 (Feb. 27, 2008).
84 16 U.S.C. § 1532(16).
85 See Policy Regarding the Recognition of Distinct Vertebrate Population Segments Under the Endangered Species
Act, 61 Fed. Reg. 4722, 4722 (Feb. 7, 1996) (henceforth “ DPS Policy”); 16 U.S.C. § 1532.
86 DPS Policy, 61 Fed. Reg. 4722.
87 T he DPS Policy considers a population discrete if it is “markedly separate from other populations” of the same
species due to “ physical, physiological, ecological, or behavioral factors.” Id. at 4725. A population may also be
considered discrete if (1) it is separated from other populations by international governmental boundaries and (2) the
legal protections differ significantly between the two countries. Id.
88 T he DPS Policy considers a population significant based on its biological and ecological significance to the species.
Id. For example, a population might be significant if it persists in an unusual or unique setting for the species, its loss
would create a significant gap in the species’ range, it represents the only surviving population in the wild that was not
reintroduced, or its genetic composition differs markedly from other populations of the species. Id.
89 Id. at 4725.
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its authority to list DPSs as species, as interpreted by the Services’ DPS policy, to designate gray
wolf populations as DPSs and delist those DPSs. The various rules designating and delisting gray
wolf DPSs and related court decisions are described below and listed in Table 1.
Final Rule Designating Eastern, Western, and Southwestern DPSs in 2003
In 2000, FWS proposed to designate four DPSs of gray wolves—the Western Great Lakes DPS,
Western DPS, Southwestern DPS, and Northeastern DPS,90 as shown in Map 2 of Figure 3—and
to delist the gray wolf in any state outside the range of those DPSs.91 FWS determined that non-
DPS states were outside the gray wolf’s current range and unlikely to be repopulated by gray
wolves, and that wolf restoration to those areas was neither potential y feasible nor necessary for
recovery.92 FWS also proposed to reclassify the gray wolves of the Western Great Lakes DPS,
Western DPS, and Northeastern DPS from endangered to threatened.93 For the Western Great
Lakes and Western DPSs, FWS determined that they were not in danger of extinction based on
the recovery progress of the western Great Lakes and northern Rocky Mountain gray wolf
populations, respectively.94 FWS determined that these populations were sufficient to ensure the
continuing viability of the DPSs as a whole.95 For the Northeastern DPS, FWS proposed to
reclassify it as threatened due to the regulatory flexibility afforded by a threatened status, rather
than based on determining that the DPS met the definition of “threatened species.”96

90 Endangered and T hreatened Wildlife and Plants; Proposal to Reclassify and Remove the Gray Wolf from the List of
Endangered and T hreatened Wildlife in Portions of the Conterminous United States; Proposal to Establish T hree
Special Regulations for T hreatened Gray Wolves, 65 Fed. Reg. 43,450, 43,450, 43,472-74, 43,476-78 (July 13, 2000).
Under the proposal, the Western Great Lakes DPS would include gray wolves in North Dakota, South Dakota,
Minnesota, Wisconsin, and Michigan; the Western DPS would include gray wolves in Washington, Oregon, Idaho,
Montana, Wyoming, Utah, Colorado, and northern parts of Arizona and New Mexico; the Southwestern D PS would
include gray wolves in southern Arizona and New Mexico, parts of southwest T exas, and Mexico; and the Northeastern
DPS would include gray wolves in New York, Vermont, New Hampshire, and Maine. Id. at 43,473.
91 Id. at 43,450, 43,476-78.
92 Id.
93 Id. at 43,450, 43,472-74, 43,476-78.
94 Id.
95 Id.
96 Id. T hough FWS provided this justification in its proposed rule, a species’ status is determined by whether it meets
the definition of endangered or threatened based on the five statutory factors. 16 U.S.C. § 1533(a).
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Figure 3. Distinct Population Segments (DPSs) in 2000 Proposed Rule and
2003 Final Rule
Designations and Listing Statuses

Source: U.S. Fish and Wildlife Service. The gray wolf has never been listed in Alaska or Hawai .
In the 2003 final rule, FWS combined and expanded the Western Great Lakes and Northeastern
DPSs to create the Eastern DPS, as shown in Map 3 of Figure 3, after not finding justification for
a separate Northeastern DPS.97 FWS reclassified the gray wolves of the Eastern DPS and the
Western DPS from endangered to threatened.98 The agency also determined that it could delist
only based on a finding of recovery, extinction, or original listing in error.99 Accordingly, FWS

97 68 Fed. Reg. 15,804, 15,859 (Apr. 1, 2003). FWS had relied on anecdotal evidence of wolf sightings when it
proposed to designate the Northeastern DPS and expected to receive more information on wolf populations in that
region during the comment period. 65 Fed. Reg. at 43,450. However, FWS received no new data on this subject, so it
determined that it could not designate a DPS without concrete evidence of a population. 68 Fed. Reg. at 15,859.
98 Id. at 15,809-11.
99 Id. at 15,826, 15,859.
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extended the three DPSs to include 12 of the states it had proposed to delist.100 The agency
delisted the gray wolf only in 14 states in the southeastern United States and in portions of
Oklahoma and Texas that FWS determined were outside the gray wolf’s historical range.101
District courts in Oregon and Vermont ultimately vacated the 2003 final rule.102 Those courts held
that FWS conflated the statutory terms “al ” and “a significant portion” when analyzing whether
the DPSs were endangered or threatened in “al or a significant portion of [their] range.”103 By
assessing what constituted “a significant portion” of the range based on which areas ensured the
continuing viability of the DPS as a whole, FWS rendered the phrase “a significant portion”
superfluous by ensuring that any DPS endangered or threatened in “a significant portion” of its
range would also be endangered or threatened in “al ” of its range.104 Those courts also concluded
that FWS violated the ESA and the DPS Policy by designating DPSs based on geographical
rather than biological criteria and by failing to conduct the five-factor analysis for wolves outside
the core recovery populations, thus reclassifying species without applying the statutory criteria.105
The Oregon district court further held that FWS combining the two DPSs and including states in
the DPSs beyond the recovered populations’ ranges was arbitrary and capricious because the gray
wolf’s conservation status varied across each DPS.106 By extending the DPSs to the gray wolf’s
historical range rather than “draw[ing] a line around a population whose conservation status
differs from other populations within that species,” the court held that FWS “invert[ed]” the
DPS’s purpose.107 The Vermont district court held that FWS violated the APA by combining the
Western Great Lakes and Northeastern DPSs into a new Eastern DPS in the 2003 final rule, which
did not appear in the proposed rule.108 The Vermont district court determined that establishing the
Eastern DPS was not a “logical outgrowth” of the proposed rule and accordingly did not provide
the public with adequate notice and opportunity for comment.109
Final Rules Designating and Delisting Western Great Lakes DPS in 2007 and
Northern Rocky Mountain DPS in 2008
After the district courts vacated the 2003 final rule, FWS adjusted its approach by individual y
designating and delisting the Western Great Lakes DPS (as shown in Figure 4) in 2007 and the
Northern Rocky Mountain DPS (as shown in Figure 5) in 2008.110 For these and later DPS rules,
FWS assessed whether each DPS met the DPS Policy’s discreteness and significance criteria.111

100 Id.
101 Id.
102 Defenders of Wildlife v. Sec’y, U.S. Dep’t of the Interior, 354 F. Supp. 2d 1156 (D. Ore. 2005); Nat’l Wildlife
Fed’n v. Norton, 386 F. Supp. 2d 553 (D. Vt. 2005).
103 Defenders of Wildlife, 354 F. Supp. 2d at 1167-69; Nat’l Wildlife Fed’n, 386 F. Supp. 2d at 565-66.
104 Defenders of Wildlife, 354 F. Supp. 2d at 1167-69; Nat’l Wildlife Fed’n, 386 F. Supp. 2d at 565-66.
105 Defenders of Wildlife, 354 F. Supp. 2d at 1171; Nat’l Wildlife Fed’n, 386 F. Supp. 2d at 563-65.
106 Defenders of Wildlife, 354 F. Supp. 2d at 1170.
107 Id.
108 Nat’l Wildlife Fed’n, 386 F. Supp. 2d at 564-65.
109 Id.
110 72 Fed. Reg. 6052, 6052 (Feb. 8, 2007); 73 Fed. Reg. 10,514, 10,514 (Feb. 27, 2008).
111 See, e.g., 72 Fed. Reg. at 6059-60; 73 Fed. Reg. at 10,519-20; Endangered and T hreatened Wildlife and Plants; 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 T hreatened Wildlife, 74 Fed. Reg. 15,070, 15,078 (Apr. 2, 2009); Endangered and
T hreatened Wildlife and Plants; Final Rule to Identify the Northern Rocky Mountain Population of Gray Wolf as a
Distinct Population Segment and to Revise the List of Endangered and T h reatened Wildlife, 74 Fed. Reg. 15,123,
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FWS determined that gray wolf populations were discrete under the DPS Policy by comparing the
distance between areas occupied by gray wolf populations to gray wolf dispersal data, finding
that the populations were separated by more than three times the average dispersal distance and
that the area in between general y was not suitable habitat for gray wolves.112 In the new final
rules, FWS determined the populations to be significant under the DPS Policy by finding that
(1) the populations occupied an unusual or unique ecological setting for the gray wolf, and
(2) losing these populations would create a significant gap in the gray wolf’s range.113 In
subsequent DPS rules, FWS would rely solely on the latter finding.114
Figure 4. Western Great Lakes Distinct Population Segment

Source: U.S. Fish and Wildlife Service.

15,128-29 (Apr. 2, 2009). FWS analyzed discreteness and significance under the DPS Policy for the 2003 rule, but its
discussion was less robust than the analysis found in the DPS rules from 2007 onward. See 68 Fed. Reg. at 15,818-19.
112 See, e.g., 72 Fed. Reg. at 6059; 73 Fed. Reg. at 10,519-20; 74 Fed. Reg. at 15,078; 74 Fed. Reg. at 15,128-29.
113 72 Fed. Reg. at 6059-60; 73 Fed. Reg. at 10,520.
114 See, e.g., 74 Fed. Reg. at 15,079; 74 Fed. Reg. at 15,129.
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In its 2007 and 2008 rulemakings, FWS also assessed whether each population had met the
recovery criteria in its recovery plan and was no longer in danger of extinction at the time or in
the foreseeable future.115 FWS found that both the Western Great Lakes and Northern Rocky
Mountain populations had met the objective criteria laid out in the recovery plans.116 It also
determined that the States of Minnesota, Michigan, and Wisconsin in the Western Great Lakes
DPS and the States of Montana and Idaho in the Northern Rocky Mountain DPS had adequate
wolf management plans in place.117 However, in the proposed rule for the Northern Rocky
Mountain DPS, FWS determined that Wyoming’s wolf management plan was inadequate to
ensure the continued recovery of the species.118 Among other concerns, FWS pointed to Wyoming
committing to manage only seven breeding packs outside the national parks119 and to Wyoming
designating the gray wolf as a predatory animal in most of the state.120 FWS stated that delisting
was contingent on Wyoming implementing an adequate wolf management plan.121 Wyoming
enacted legislation in February 2007 removing statutory obstacles to the revisions FWS required,
and the Wyoming Fish and Game Commission approved the revised plan in November 2007.122
In the 2008 final rule, FWS determined that Wyoming’s plan would adequately ensure the
continued recovery of the gray wolf population there.123

115 72 Fed. Reg. 6052, 6052 (Feb. 8, 2007); 73 Fed. Reg. 10,514, 10,514 (Feb. 27, 2008).
116 72 Fed. Reg. at 6052-56; 73 Fed. Reg. at 10,520-26.
117 72 Fed. Reg. at 6083-95; 73 Fed. Reg. at 10,546-49.
118 72 Fed. Reg. at 6134.
119 T he recovery criteria in the Northern Rocky Mountain Wolf Recovery Plan established 10 breeding pairs in each of
the 3 recovery areas—northern Montana, central Idaho, and the greater Yellowstone area— as a minimum recovery
level. Northern Rocky Mountain Wolf Recovery Plan , U.S. FISH & WILDLIFE SERV., at 10 (1987). To ensure the
populations’ continued recovery, FWS determined that each state (Montana, Idaho, and Wyoming) should commit to
managing their populations to maintain at least 15 breeding pairs. See, e.g., 73 Fed. Reg. at 10,522; Endangered and
T hreatened Wildlife and Plants; Removal of the Gray Wolf in Wyoming from the Federal List of Endangered and
T hreatened Wildlife and Removal of the Wyoming Wolf Population’s Status as an Experimental Population, 77 Fed.
Reg. 55,530, 55,538 (Sept. 10, 2012). Wyoming’s gray wolf population was differently situated from the other two
states because most of the gray wolves in the greater Yellowstone area occupy land within the boundaries of national
parks, such as Yellowstone National Park. Id.
120 According to FWS, classifying the wolf as a “predatory animal” under Wyoming law means the animal is “under the
jurisdiction of the Wyoming Department of Agriculture and may be taken by anyone, anywhere in the predatory animal
area, at any time, without limit, and by any means[.]” 72 Fed. Reg. at 6129.
121 Id. at 6106.
122 Endangered and T hreatened Wildlife and Plants; Designating the Northern Rocky Mountain Population of Grey
Wolf as a Distinct Population Segment and Removing this Distinct Population Segment from the Federal List of
Endangered and T hreatened Wildlife, 72 Fed. Reg. 36,939, 36,940 (July 6, 2007).
123 73 Fed. Reg. at 10,514, 10,552-55.
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Figure 5. Northern Rocky Mountain Distinct Population Segment

Source: U.S. Fish and Wildlife Service.
Much like the 2003 rule, courts also vacated these final rules.124 For the 2007 Western Great
Lakes DPS final rule, a federal district court in the District of Columbia held that the ESA was
ambiguous about whether FWS could designate for delisting purposes a DPS from a listed full
species if FWS had never listed the DPS specifical y.125 However, FWS had argued that the ESA
was unambiguous and the plain meaning of the text supported its authority to designate and delist
a DPS from a listed full species.126 Because FWS had relied on the ESA’s plain language rather
than interpreting the text, the court determined there was no FWS interpretation to defer to under

124 Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp. 2d 7 (D.D.C. 2008); Defenders of Wildlife v. Hall, No.
9:08-cv-00056 (Oct. 14, 2008) (order vacating and remanding rule to FWS and dismissing case with prejudice).
125 Humane Soc’y of the U.S., 579 F. Supp. 2d at 17.
126 Id. at 19-20.
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the Chevron doctrine.127 The court vacated the rule and remanded it to FWS to interpret the
ambiguous statutory language.128
For the 2008 Northern Rocky Mountain DPS final rule, a federal court in Montana reviewed
FWS’s rule when it granted a motion to enjoin the rule while litigation proceeded.129 To issue a
preliminary injunction, a court must find, among other things, that the plaintiffs have a likelihood
of success on the merits of the case.130 The court determined the plaintiffs were likely to prevail
based on two arguments. First, the court determined that FWS likely had been arbitrary and
capricious by inadequately explaining why its final rule ignored the recovery plan criterion of
genetic exchange between gray wolves from different recovery areas (i.e., central Idaho,
northwestern Montana, and the greater Yel owstone area).131 Genetic exchange had been included
as a recovery criterion in a 1994 environmental impact statement prepared to evaluate the
environmental impacts of introducing the experimental gray wolf populations into central Idaho
and the greater Yel owstone area.132 The court held that although FWS did not have to rely on
recovery criteria to find that a species had recovered, the agency needed to explain its decision to
ignore such criteria adequately.133 Second, the court determined that FWS was arbitrary and
capricious in approving Wyoming’s wolf management plan—part of the recovery criteria—
because, in the court’s view, FWS’s reasons for rejecting previous Wyoming plans applied
equal y to the 2007 one.134 After issuing the preliminary injunction, the court granted FWS’s
request to vacate the rule and remand it.135
Final Rules Designating and Delisting Western Great Lakes DPS and Northern
Rocky Mountain DPS Except Wyoming in 2009
In 2009, FWS again published final rules designating and delisting the Western Great Lakes DPS
and the Northern Rocky Mountain DPS, except it did not delist the gray wolf in Wyoming after
finding the state’s management plan inadequate.136 FWS issued the final Western Great Lakes
DPS rule, which interpreted FWS’s authority to designate and delist DPSs from listed species to
address the concerns raised by the D.C. district court’s 2008 ruling, without issuing a new
proposed rule.137 Parties chal enged the latest Western Great Lakes DPS rule for, among other

127 Id.
128 Id.
129 Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160 (D. Mont. 2008).
130 Id. at 1167 (citing Nat’l Wildlife Fed’n v. Nat’l Marine Fisheries Serv., 422 F.3d 782, 795 (9th Cir. 2005)).
131 FWS argued that the criterion did not require evidence of actual genetic exchange, only the potential for likely
genetic exchange; the court disagreed. Id. at 1169-70.
132 Id. at 1169-71.
133 Id.
134 Id. at 1172-75.
135 Endangered and T hreatened Wildlife and Plants; Designating the Northern Rocky Mountain Population of Gray
Wolf as a Distinct Population Segment and Removing this Distinct Population Segment from the Federal List of
Endangered and T hreatened Wildlife, 73 Fed. Reg. 63,926, 63,926 (Oct. 28, 2008); Defenders of Wildlife v. Hall, No.
9:08-cv-00056 (Oct. 14, 2008) (order vacating and remanding rule to FWS and dismissing case with prejudice).
136 74 Fed. Reg. 15,070 (Apr. 2, 2009); 74 Fed. Reg. 15,123 (Apr. 2, 2009 ).
137 74 Fed. Reg. at 15,075-78.
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things, violating the APA’s notice and comment requirements.138 Pursuant to a settlement
agreement, FWS ultimately withdrew the rule.139
The Montana district court vacated the 2009 Northern Rocky Mountain DPS rule after concluding
that the ESA did not al ow FWS to list a partial DPS (i.e., listing the gray wolf only in the
Wyoming segment of the DPS).140 FWS had interpreted the statutory phrase “significant portion
of its range” in the endangered species and threatened species definitions to al ow a species to be
listed for only that portion of its range where the Services determine the species is endangered or
threatened.141 The court rejected this interpretation as impermissible under the Act and vacated
the rule.142 It held that the plain language of the ESA precluded listing a smal er classification
than a DPS.143 The court also held that FWS’s interpretation rendered superfluous Congress’s
addition of DPS to the definition of “species” and Congress’s restriction of DPSs to vertebrate
species because under FWS’s interpretation, the agency could simply list the full species or
subspecies for only the range occupied by the DPS and achieve the same result without the DPS
designation and for any species—vertebrate or not.144 However, an act of Congress in 2011
directed FWS to reinstate the 2009 rule designating and delisting the Northern Rocky Mountain
DPS without Wyoming.145
Final Rule Designating and Delisting Western Great Lakes DPS in 2011
FWS published another final rule designating and delisting the Western Great Lakes DPS in
2011.146 In the proposed rule, FWS also proposed to recognize the eastern timber wolf as a full
species (C. lycaon) rather than a subspecies of gray wolf (C. lupus lycaon) based on
developments in taxonomic research.147 In recognizing the eastern timber wolf as a full species,
FWS proposed to delist the gray wolf in al or part of 29 states (outside the Western Great Lakes
DPS) where FWS determined that the areas were part of the historical range of the eastern timber
wolf or red wolf (C. rufus) rather than the gray wolf (C. lupus).148 In the 2011 Western Great
Lakes DPS final rule, however, FWS determined that the scientific community had not reached a
consensus on whether the eastern timber wolf was a full species.149 FWS accordingly continued to
recognize the eastern timber wolf as a subspecies of gray wolf until the scientific debate was

138 Humane Soc’y of the U.S. v. Salazar, No. 1:09-CV-1092 (D.D.C. June 15, 2009) (complaint).
139 Humane Soc’y of the U.S. v. Salazar, No. 1:09-CV-1092 (D.D.C. July 2, 2009) (settlement order).
140 Defenders of Wildlife v. Salazar, 812 F. Supp. 2d 1205, 1207 (D. Mont. 2009).
141 Id. at 1218.
142 Id. at 1221-22.
143 Id. at 1218-24.
144 Id.
145 Department of Defense and Full-Year Appropriations Act, 2011, Pub. L. No. 112-10, § 1713, 125 Stat. 150 (2011).
Parties challenged this legislation as unconstitutional for violating the separation -of-powers doctrine. Alliance for the
Wild Rockies v. Salazar, 800 F. Supp. 2d 1123 (D. Mont. 2011). A court upheld the legisla tion, holding that Congress
substantively amended the ESA and did not direct the federal courts to make specific findings about the rule’s validity
under the ESA. Id.; Alliance for the Wild Rockies v. Salazar, 672 F.3d 1170, 1175 (9th Cir. 2012).
146 Endangered and T hreatened Wildlife and Plants; Revising the Listing of the Gray Wolf (Canis lupus) in the Western
Great Lakes, 76 Fed. Reg. 81,666 (Dec. 28, 2011).
147 Endangered and T hreatened Wildlife and Plants; Proposed Rule to Revise the List of Endangered and T hreatened
Wildlife for the Gray Wolf (Canis lupus) in the Eastern United States, Initiation of Status Reviews for the Gray Wolf
and for the Eastern Wolf (Canis lycaon), 76 Fed. Reg. 26,086, 26,088 (May 5, 2011).
148 Id. at 26,086-88.
149 76 Fed. Reg. at 81,669.
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resolved and postponed delisting in the 29 states and partial states.150 FWS otherwise finalized the
rule as proposed, relying on data and analysis similar to what it had used in prior rules
designating and delisting the Western Great Lakes DPS.151
A district court in the District of Columbia vacated the 2011 Western Great Lakes DPS rule in
2014.152 The court reviewed FWS’s interpretation of its statutory authority under the ESA to
designate and delist a DPS from a listed full species, which the agency adopted after the 2008
opinion vacating FWS’s 2007 Western Great Lakes DPS rule that relied on the plain meaning of
the ESA.153 On appeal, the U.S. Court of Appeals for the District of Columbia Circuit (D.C.
Circuit) held in 2017 that FWS could designate and delist DPSs from listed full species but that
FWS had failed to do so properly in the 2011 rule.154 The court concluded that the 2011 Western
Great Lakes DPS rule was arbitrary and capricious because FWS had improperly conducted its
analysis by failing to consider two factors: (1) the effect of delisting the DPS on the remainder of
the species and (2) the loss of the gray wolf’s historical range when analyzing threats to the
species.155
Final Rule Delisting the Gray Wolf in Wyoming in 2012
After approving its revised state laws and wolf management plan, FWS delisted the gray wolf in
Wyoming in 2012.156 The federal district court in the District of Columbia vacated the rule after
finding it was arbitrary and capricious for FWS to rely on nonbinding promises in Wyoming’s
management plan to determine the state’s regulatory mechanisms were adequate.157 The D.C.
Circuit reversed the federal district court, holding that the ESA did not limit FWS to considering
only legal y binding regulatory mechanisms to determine whether the regulatory mechanisms
were adequate to protect the species.158 The rule delisting the gray wolf in Wyoming was
accordingly reinstated.159
Delisting the Gray Wolf Listed Entities
Beginning in 2013, FWS delisting proposals have examined the gray wolf entities that were listed
through FWS’s various rulemakings (referred to as the “listed entities”) rather than attempting to
list or delist gray wolf DPSs. As discussed in more detail below, in 2013, FWS proposed to delist
the gray wolf entities (at the time, (1) the gray wolf in Minnesota and (2) the gray wolf in the

150 Id. at 81,666, 81,669.
151 Id. at 81,721-23.
152 Humane Soc’y of the U.S. v. Jewell, 76 F. Supp. 2d 69, 110-13 (D.D.C. 2014).
153 Id.
154 Humane Soc’y of the U.S. v. Zinke, 865 F.3d 585, 600-07 (D.C. Cir. 2017).
155 Id.
156 77 Fed. Reg. 55,530 (Sept. 10, 2012). T he gray wolf in Wyoming is not a species, subspecies, or DPS. However, as
discussed above, the 2011 legislation directed FWS to reinstate the rule delisting the gray wolf in the Northern Rocky
Mountain DPS, except for in Wyoming, leaving the gray wolf in Wyoming listed. Department of Defense and Full-
Year Appropriations Act, 2011, Pub. L. No. 112-10, § 1713, 125 Stat. 150 (2011). In the proposed and final rules, FWS
assessed the status and recovery of the gray wolf in Wyoming in the context of being part of the Northern Rocky
Mountain DPS. 76 Fed. Reg. 61,782 (Oct. 5, 2011) (proposed rule); 77 Fed. Reg. 55,530 (Sept. 10, 2012) (final rule).
157 Defenders of Wildlife v. Jewell, 68 F. Supp. 3d 193, 203 -10 (D.D.C. 2014).
158 Defenders of Wildlife v. Zinke, 849 F.3d 1077, 1082-84, 1093 (D.C. Cir. 2017).
159 Endangered and T hreatened Wildlife and Plants; Reinst atement of Removal of Federal Protections for Gray Wolves
in Wyoming, 82 Fed. Reg. 20,284 (May 1, 2017).
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lower 48 states—other than Minnesota, the Northern Rocky Mountain DPS, and the Western
Great Lakes DPS—and Mexico) and relist the Mexican wolf (C. lupus baileyi), a subspecies of
the gray wolf, as endangered.160 However, FWS finalized the Mexican wolf listing in 2015 as a
separate listing without finalizing the delisting component of the proposed rule.161 In that rule,
FWS revised the gray wolf listing for the lower 48 states that had previously included the
Mexican wolf’s territory in New Mexico and Arizona to exclude that area.162 FWS published a
new proposed rule in 2019 to delist the listed entities other than the Mexican wolf.163 At the time,
the listed entities were (1) the gray wolf in Minnesota; and (2) the gray wolf in the lower 48 states
and Mexico, except for gray wolves in Minnesota, the Northern Rocky Mountain DPS of gray
wolves, and the Mexican wolf. In November 2020, FWS published a final rule removing these
two gray wolf entities from the list of endangered and threatened species effective January 4,
2021, but leaving the Mexican wolf listed as endangered.164
2013 Proposed Rule to Delist Gray Wolf Listed Entities and List Mexican Wolf
In 2013, FWS proposed to delist the gray wolf in the lower 48 states and Mexico and list the
Mexican wolf—a gray wolf subspecies—as endangered.165 At the time FWS published the 2013
proposed rule, the Northern Rocky Mountain DPS (including Wyoming) and the Western Great
Lakes DPS were already delisted.166 In the proposed rule, FWS concluded that the gray wolf as
listed at the time (i.e., gray wolves found in the lower 48 states that were not part of the Western
Great Lakes or Northern Rocky Mountain DPSs) did not qualify as a “species” under the ESA,
which is a requirement for listing under the Act.167 FWS noted that the listed entity was not an
entire species or subspecies of gray wolf.168 It also concluded that the listed entity did not
describe a valid “population” of gray wolves that could qualify as a DPS, and accordingly was
not a “species.”169
FWS then evaluated whether the gray wolf as a taxonomical species or any subspecies or DPSs of
the gray wolf merited listing as an endangered or threatened species.170 FWS determined first that

160 Endangered and T hreatened Wildlife and Plants; Removing the Gray Wolf (Canis lupus) from the List of
Endangered and T hreatened Wildlife and Maintaining Protections for the Mexican Wolf (Canis lupus baileyi) by
Listing It as Endangered, 78 Fed. Reg. 35,664 (June 13, 2013).
161 Endangered and T hreatened Wildlife and Plants; Endangered Status for the Mexican Wolf, 80 Fed. Reg. 2488 (Jan.
16, 2015).
162 Id. at 2511.
163 Endangered and T hreatened Wildlife and Plants; Removing the Gray Wolf ( Canis lupus) from the List of
Endangered and T hreatened Wildlife, 84 Fed. Reg. 9648, 9686 (Mar. 15, 2019). For the status at the time of the
proposed rule, see Table 1.
164 Endangered and T hreatened Wildlife and Plants; Removing the Gray Wolf (Canis lupus) from the List of
Endangered and T hreatened Wildlife, 85 Fed. Reg. 69,778 (Nov. 3, 2020).
165 78 Fed. Reg. 35,664 (June 13, 2013). As a reminder, the ESA definition of species includes subspecies and DPSs.
16 U.S.C. § 1532(16).
166 T he rules delisting the gray wolf in Wyoming and the Western Great Lakes DPS were subsequently vacated by
courts in 2014. Humane Soc’y of the U.S. v. Jewell, 76 F. Supp. 2d 69, 110-13 (D.D.C. 2014), aff’d by Humane Soc’y
of the U.S. v. Zinke, 865 F.3d 585, 614-15 (D.C. Cir. 2017); Defenders of Wildlife v. Jewell, 68 F. Supp. 3d 193, 203 -
10 (D.D.C. 2014). T he latter was later ordered to be reinstated by the D.C. Circuit in 2017 . Defenders of Wildlife v.
Zinke, 849 F.3d 1077, 1082-84, 1093 (D.C. Cir. 2017).
167 78 Fed. Reg. at 35,673-78, 35,695.
168 Id. at 35,673.
169 Id. at 35,673-74.
170 Id. at 35,673-78, 35,695.
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the gray wolf as a whole did not merit listing.171 FWS concluded that based on the best available
data, there were three subspecies of gray wolf and, of the three, only the Mexican wolf was
listable as endangered and the other two did not merit listing.172 Further, FWS did not identify any
listable DPSs of the gray wolf.173 In particular, FWS determined that gray wolves that had been
sighted in the Pacific Northwest did not qualify as a DPS because it was not a population and, in
any event, were not discrete from the Northern Rocky Mountain DPS population.174 Having
concluded that the listed entities did not qualify as a species, and finding only one listable species
or DPS—the Mexican wolf, FWS proposed to delist the gray wolf where it was stil listed and list
the Mexican wolf as an endangered species.175
In 2014, as discussed above, federal courts in the District of Columbia vacated the 2011 and 2012
rules delisting the Western Great Lakes DPS and delisting the gray wolf in Wyoming.176
Following these court decisions, in 2015 FWS finalized its 2013 proposal to list the Mexican wolf
as endangered, but it did not finalize the rest of the proposed rule pertaining to delisting the gray
wolf.177 In that rule, FWS adjusted the listing for the gray wolf in the lower 48 states and Mexico
to exclude the Mexican wolf’s territory in Arizona and New Mexico from the territory over which
the gray wolf is endangered.178
2020 Rule Delisting the Gray Wolf Listed Entities Except the Mexican Wolf
In 2019, FWS published a proposed rule to delist two gray wolf listed entities: (1) the gray wolf
in Minnesota and (2) the gray wolf in the lower 48 states and Mexico, except for the gray wolves:
(a) in Minnesota, (b) in the Northern Rocky Mountain DPS, and (c) that are part of the gray wolf
subspecies, the Mexican wolf.179 Though the listed entities had changed since the 2013 proposed
rule, the effect would be the same—delisting al gray wolves except the Mexican wolf. The
proposed rule did not address or affect the Mexican wolf that was listed separately in 2015.180 On

171 Id. at 35,673-74.
172 FWS recognized the following three gray wolf subspecies: C. lupus nubilus (found in the coastal areas of Alaska
and Canada and the Pacific Northwest to the Great Lakes region), C. lupus occidentalis (found in the interior of Canada
and the northern Rocky Mountains), and C. lupus baileyi (historically found in the American Southwest and Mexico).
Id. at 35,717, 35,670-73.
173 Id. at 35,675-77. In its analysis, FWS also revisited the gray wolf’s taxonomy, determining that scientific evidence
supported recognizing the eastern wolf as a full species, C. lycaon, separate from the gray wolf. Id. at 35,717, 35,670-
73.
174 Id. at 35,675-77.
175 Id. at 35,718.
176 Humane Soc’y of the U.S. v. Jewell, 76 F. Supp. 2d 69, 110-13 (D.D.C. 2014), aff’d by Humane Soc’y of the U.S. v.
Zinke, 865 F.3d 585, 614-15 (D.C. Cir. 2017); Defenders of Wildlife v. Jewell, 68 F. Supp. 3d 193, 203 -10 (D.D.C.
2014). T he latter was later ordered to be reinstated by the D.C. Circuit in 2017 . Defenders of Wildlife v. Zinke, 849
F.3d 1077, 1082-84, 1093 (D.C. Cir. 2017). For more information on these decisions, see “ Final Rule Designating and
Delisting Western Great Lakes DPS in 2011 ” and “ Final Rule Delisting the Gray Wolf in Wyoming in 2012 .”
177 80 Fed. Reg. 2488 (Jan. 16, 2015).
178 Id. at 2511.
179 Endangered and T hreatened Wildlife and Plants; Removing the Gray Wolf (Canis lupus) from the List of
Endangered and T hreatened Wildlife, 84 Fed. Reg. 9648, 9686 (Mar. 15, 2019). For the status at the time of the
proposed rule, see Table 1.
180 84 Fed. Reg. at 9686; Endangered and T hreatened Wildlife and Plants; Endangered Status for the Mexican Wolf, 80
Fed. Reg. 2488 (Jan. 16, 2015).
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November 3, 2020, FWS published a final rule, effective January 4, 2021, delisting the gray wolf
listed entities except for the Mexican wolf, which remains listed as endangered.181
In the final rule, FWS concluded that the two listed entities are not “species” as defined by the
Act, which is a requirement for listing.182 FWS observed that neither listed entity encompassed
the entire taxonomic species or any subspecies of gray wolf, and accordingly could only be
listable as DPSs.183 Neither listed entity qualified as a DPS, according to the FWS, because
neither was discrete—the Minnesota wolves were not discrete from the remainder of the Western
Great Lakes population, and the remaining entity listed as endangered was not discrete from the
Minnesota wolves or the Northern Rocky Mountain DPS wolves.184 FWS also assessed the status
of various gray wolf groups (i.e., whether they are threatened or endangered species), assessing
the two listed entities, separately and combined, as wel as the two listed entities combined plus
the Northern Rocky Mountain DPS wolves.185 FWS concluded that those various combinations of
the gray wolf listed entities did not qualify as endangered species or threatened species under the
Act.186 Pursuant to its determination that the listed entities did not qualify as species and its
finding that the entities, separately or combined, did not qualify as endangered or threatened,
FWS delisted the gray wolf entities.187 As mentioned, the final rule did not affect the listing for
the Mexican wolf.188
The gray wolf is accordingly, as of January 4, 2021, delisted in the lower 48 states and Mexico,
although the Mexican wolf remains listed as endangered. Several environmental groups have
provided a notice of intent to sue to the Secretary of the Interior and Director of FWS, al eging
that the final rule violates the ESA.189 Table 1 summarizes the history of listing, recovery, and
delisting by DPS or region (described further in the “History of Listing and Delisting the Gray
Wolf” section), and Table A-1 in this report’s Appendix provides a more detailed timeline.

181 85 Fed. Reg. 69,778 (Nov. 3, 2020).
182 Id. at 69,783-85.
183 Id. at 69,783.
184 Id. at 69,783-84.
185 Id. at 69,784-85.
186 Id. at 69,882, 69,885-86, 69,889, 69,893.
187 Id. at 69,778. FWS also returned to its position that the scientific community had not yet reached a consensus that
the eastern wolf is a full species. Id. at 69,785-86.
188 Id. at 69,778.
189 Letter from Kristen L. Boyles & T imothy J. Preso, EarthJustice, to David Bernhardt, Sec’y, Dep’t of the Interior, &
Aurelia Skipwith, Dir., U.S. Fish & Wildlife Serv. (Nov. 5, 2020),
https://www.biologicaldiversity.org/campaigns/gray_wolves/pdfs/Gray-Wolf-60-Day-Notice.pdf.
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Table 1. Timeline: Gray Wolf Status by Population
Western Great Lakes
Northern Rocky
Southwestern
Remaining
Date
Population
Mountain Population
Population
Lower 48 States
3/11/1967
Eastern timber wolf (C.

lupus lycaon) listed
1/15/1973

Northern Rocky Mountain

wolf (C. lupus irremotus)
listed
4/28/1976

Mexican wolf (C.

lupus baileyi) listed
6/14/1976

Texas wolf (C.

lupus monstrabilis)
listed
3/9/1978
Gray wolf listings consolidated to list as ful species in lower 48 states except in Minnesota;
Minnesota gray wolf listed as threatened
11/22/1994

Experimental populations

introduced
1/12/1998

Experimental

population
introduced
4/1/2003
Eastern (combining Western Great Lakes and Northeastern DPSs),
Western, and Southwestern DPSs designated;
Eastern and Western DPSs reclassified as threatened
1/31/2005
Eastern, Western, and Southwestern DPSs invalidated by Oregon district court;
ful listing as endangered restored
3/18/2005

Court dismissed

Wyoming’s suit chal enging
FWS’s finding that the
state’s management plan
was inadequate
8/19/2005
Eastern, Western, and Southwestern DPSs also invalidated by Vermont district court
2/8/2007
Designated as DPS and

delisted
2/27/2008

Designated as DPS and

delisted
7/18/2008

Court granted preliminary

injunction and stays
delisting rule
9/29/2008
Court vacated delisting

rule
10/14/2008

Court vacated delisting

rule
12/11/2008
Listing reinstated

4/2/2009
Designated as DPS and
Designated as DPS and

delisted
delisted except in
Wyoming
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Western Great Lakes
Northern Rocky
Southwestern
Remaining
Date
Population
Mountain Population
Population
Lower 48 States
8/1/2017
Appeals court affirmed

district court opinion
vacating delisting rule
11/3/2020
Gray wolf delisted except the Mexican wolf (C. lupus baileyi) subspecies
Status
Delisted
Delisted
Mexican wolf
Delisted
Effective
(C. lupus baileyi)
1/4/2021 a
listed as
endangered
Source: Congressional Research Service.
Notes: DPS = Distinct Population Segment; FWS = U.S. Fish and Wildlife Service.
a. January 4, 2021, is the effective date of the November, 3, 2020 final rule.
Challenges When Listing and Delisting Species
FWS has encountered a host of legal chal enges when listing or delisting the gray wolf.190 This
section reviews by topic the substantive chal enges FWS has encountered in rulemaking and
litigation. Though specific to the gray wolf, the chal enges FWS has faced provide insight into the
issues the Services general y encounter with listing and delisting species and how courts may
react to the Services’ approaches.
Identifying the Species
To identify a species as endangered or threatened, the Services must first identify what qualifies
as a “species” under the Act. When the ESA was enacted in 1973, it defined a species to include
“any subspecies of fish or wildlife or plants and any other group of fish or wildlife of the same
species or smal er taxa in common spatial arrangement that interbreed when mature.”191 In 1978,
Congress amended the ESA to define species to include “any subspecies of fish or wildlife or
plants, and any distinct population segment of any species of vertebrate fish or wildlife which
interbreeds when mature.”192 Species and subspecies are biological concepts used in taxonomic
classification.193 As such, the Services consult experts in those fields to identify listable species
and subspecies based on the best available scientific data.194 A DPS, however, is a statutory
creation, not a biological concept.195 In 1996, the Services implemented the DPS Policy to outline
how they would evaluate DPSs.196 Under the policy, a population must be discrete from other

190 See, e.g., Defenders of Wildlife v. Sec’y, U.S. Dep’t of the Interior, 354 F. Supp. 2d 1156 (D. Ore. 2005) ; Nat’l
Wildlife Fed’n v. Norton, 386 F. Supp. 2d 553 (D. Vt. 2005); Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp.
2d 7 (D.D.C. 2008); Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160 (D. Mont. 2008) ; Defenders of Wildlife v.
Salazar, 729 F. Supp. 2d 1207 (D. Mont. 2010); Humane Soc’y of the U.S. v. Jewell, 76 F. Supp. 3d 69 (D.D.C. 2014),
aff’d on other grounds Humane Soc’y of the U.S. v. Zinke, 865 F.3d 585 (D.C. Cir. 2017) .
191 Pub. L. No. 93-205, § 3, 87 Stat. 886 (1973).
192 Pub. L. No. 95-632, § 2, 92 Stat. 3752 (1978) (emphasis added).
193 See, e.g., SCIENCE AND THE ENDANGERED SPECIES ACT, NAT’L RESEARCH COUNCIL, NAT’L ACADEMY OF SCI. 56-57
(1995) (henceforth “NAS ESA Report”).
194 See, e.g., 78 Fed. Reg. 35,664, 35,669-73 (June 13, 2013).
195 DPS Policy, 61 Fed. Reg. at 4722.
196 Id.
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populations, significant in accordance with principles of conservation biology, and endangered or
threatened to be listed as a DPS.197
Applying these criteria in practice has proven difficult. For the gray wolf in particular, FWS has
encountered chal enges with the wolf’s taxonomy and with regulating segments of the wolf
population.
Taxonomy
Many of FWS’s rulemaking preambles detail the difficulties involved in identifying listable
entities and analyzing them in light of disagreements over the taxonomic classification of wolf
species and subspecies. Under the ESA, FWS must be able to identify a listable entity—a full
species, a subspecies, or a DPS—to analyze its status for listing.198 The entity identified for
analysis determines the population(s), historical and current range, and threats that the Services
consider. Though FWS’s determinations about gray wolf taxonomy general y have not been
subject to direct legal chal enges, they underpin how FWS conducts the remainder of its analyses
to assess the species’ status. Changing views and a lack of scientific consensus over the
taxonomic classifications for the gray wolf have caused FWS to revise its analyses during or
between rulemakings.199
The Services must base decisions about what entity to evaluate on the “best scientific and
commercial data available.”200 But scientists do not always agree on their taxonomic
conclusions.201 Taxonomists may classify species based on distinctive physical or behavioral
traits, evolutionary pathways, interbreeding capabilities, or genetic composition.202 Taxonomists
may disagree about whether and how to recognize subspecies within a species. Differences in
methodology or datasets may also lead to disagreements about the taxonomic level to assign a
particular entity. For example, various scientific studies have concluded that the eastern timber
wolf is a full species (C. lycaon), a subspecies of gray wolf (C. lupus lycaon), a hybrid of
different wolf species, a wolf-coyote hybrid, or a distinct gray wolf population not rising to the
level of a subspecies.203 Different methodological approaches may also affect how many entities
within a species taxonomists recognize as distinct. For example, FWS has observed that scientific
studies had recognized as many as 24 subspecies of wolves in North America but that other
taxonomists had suggested there were actual y 5 or fewer subspecies.204 From these divergent
scientific studies, the Services must determine what classification for an entity the “best scientific
and commercial data available” support.

197 Id. at 4725.
198 16 U.S.C. §§ 1532(16) & 1533(a). T he ESA defines species to include subspecies and DPSs. Id. T he term “full
species” does not appear in the statute but is used here to distinguish a taxonomic species from species as it is used in
the ESA.
199 Compare 76 Fed. Reg. 26,086, 26,088-89 (May 5, 2011), with 76 Fed. Reg. 81,666, 81,668-69 (Dec. 28, 2011);
com pare 78 Fed. Reg. 35,664, 35,669-70 (June 13, 2013), with 84 Fed. Reg. 9648, 9654-55 (Mar. 15, 2019).
200 16 U.S.C. § 1533(b)(1).
201 See, e.g., 78 Fed. Reg. at 35,670-73; 84 Fed. Reg. at 9654-55.
202 See, e.g., NAS ESA REPORT, supra note 193, at 51-54; 78 Fed. Reg. at 35,670-73.
203 See, e.g., 76 Fed. Reg. 26,086, 26,088-89 (May 5, 2011); 78 Fed. Reg. at 35,669-70.
204 Endangered and T hreatened Wildlife and Plants; Proposed Establishment of a Nonessential Experimental
Population of Gray Wolf in Yellowstone National Park in Wyoming, Idaho, and Montana, 59 Fed. Reg. 42,108, 42,108
(Aug. 16, 1994).
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The Services may also conclude that there is no scientific consensus on an entity’s taxonomic
status that would be defensible based on the data.205 For example, twice FWS has proposed to
recognize the eastern timber wolf as a full species only to conclude later that the scientific
community had not reached a consensus on its classification.206 In each case, FWS reverted to the
eastern timber wolf’s original classification as a subspecies of gray wolf (C. lupus lycaon).207 It is
unclear how FWS would have proceeded if it could not have reverted to a status quo. Any
determination on taxonomic classification for listing purposes must be defensible based on the
best scientific and commercial data available.208
Classifications may also change over time as scientists reevaluate their conclusions based on
additional data or improved methodologies.209 In its 2013 proposed rule, FWS determined that it
would recognize only three gray wolf subspecies out of as many as 24 identified historical y—C.
lupus nubilus (coastal wolf), C. lupus occidentalis (interior and mountain wolf), and C. lupus
baileyi (Mexican wolf).210 As described above, FWS has continued to evaluate the taxonomic
status of the eastern timber wolf as scientific research and opinion evolves.211
Changing classifications and disagreements within the scientific community may result in a
previously listed entity no longer qualifying as a “species” under the ESA or in the Services being
unable to identify any listable entity that qualifies as endangered or threatened. Such changes and
disagreements can also affect other aspects of the Services’ status analysis. For example, which
areas FWS recognizes as comprising the gray wolf’s current and historical range depends on
whether the eastern timber wolf is a subspecies of gray wolf or a separate full species.212 Any
areas solely occupied by the eastern timber wolf would be included in the gray wolf’s range only
if the eastern timber wolf is a subspecies. When FWS proposed to recognize the eastern timber
wolf as a full species in 2011, it also proposed removing certain areas from the gray wolf listing
that FWS considered listed in error because it determined that the wolves occupying those areas
were eastern timber wolves rather than gray wolves.213 In addition, the Services use a species’
current range to determine the species’ status (i.e., whether it is endangered or threatened in “al
or a significant portion of its range”214) and use the historical range to assess threats against the
species’ continued existence.215 Accordingly, changes to how a species is classified and defined
can affect the Services’ analysis of the species’ status.
Defining DPSs
FWS’s efforts to designate and delist gray wolf DPSs have given rise to multiple legal chal enges
and vacated rules. To designate gray wolf DPSs, FWS has applied the DPS Policy. Under the

205 See, e.g., 76 Fed. Reg. at 26,088-89; 78 Fed. Reg. at 35,669-70.
206 Compare 76 Fed. Reg. at 26,088-89, with 76 Fed. Reg. 81,666, 81,668-69 (Dec. 28, 2011); compare 78 Fed. Reg. at
35,669-70, with 84 Fed. Reg. 9648, 9654-55 (Mar. 15, 2019).
207 76 Fed. Reg. at 81,668-69; 84 Fed. Reg. at 9654-55.
208 16 U.S.C. § 1533(b).
209 See, e.g., 78 Fed. Reg. at 35,670-73; 84 Fed. Reg. at 9654-55.
210 78 Fed. Reg. at 35,670-73.
211 Compare 76 Fed. Reg. at 26,088-89, with 76 Fed. Reg. 81,666, 81,668-69 (Dec. 28, 2011); compare 78 Fed. Reg. at
35,669-70, with 84 Fed. Reg. 9648, 9654-55 (Mar. 15, 2019).
212 76 Fed. Reg. at 26,088-89; 78 Fed. Reg. at 35,669-70.
213 76 Fed. Reg. at 26,142.
214 See 16 U.S.C. § 1532(6) & (20) (emphasis added).
215 See, e.g., 84 Fed. Reg. 9648, 9658 (Mar. 15, 2019).
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policy, the Services may designate a DPS if it is discrete from the remainder of the species and
significant to the species.216 The Services determine a population is discrete if it is “markedly
separate” from other populations based on “physical, physiological, ecological, or behavioral
factors” or international boundaries.217 The Services determine that a population is significant—
biological y and ecological y—based on whether the population persists in an unusual setting for
the species, differs markedly from the rest of the species genetical y, represents the only natural y
occurring population in the wild (i.e., excluding reintroduced populations), or would create a gap
in the species range if the population were lost.218 The Services imposed the significance criteria
to ensure they use the DPS designation authority “sparingly,” consistent with congressional
guidance, to avoid potential abuse, such as listing numerous populations of otherwise abundant
species.219 If the Services determine a population meets the discreteness and significance criteria,
they evaluate the DPS’s status to determine whether it is endangered or threatened in accordance
with the ESA definitions and factors.220
For the gray wolf, FWS has general y evaluated discreteness by determining the distance between
the areas occupied by different populations against average dispersal distances.221 The agency
determined that the distances between the Western Great Lakes, Northern Rocky Mountain, and
Mexican wolf populations were al greater than three times the average dispersal distance for a
lone wolf, leading FWS to determine that each population is discrete. FWS also has used the
Canada-U.S. border to demarcate DPSs based on the different regulatory regimes in the two
countries.222 FWS determined the Western Great Lakes and Northern Rocky Mountain DPSs were
significant because losing either population would leave a significant gap in the gray wolf’s
range.223 In the 2003 rulemaking, FWS also determined that the Western Great Lakes, Western
(later Northern Rocky Mountain), and Mexican wolf populations each displayed distinct
morphological traits that could represent different subspecies, presumably meaning they were
genetical y distinct.224 In the 2007 rule, FWS also concluded that the Western Great Lakes DPS
persisted in a unique environment due to its presence in the Laurentian Mixed Forest Province
where the boreal forest transitions to the broadleaf deciduous forest.225 However, it did not rely on
those factors in later rules.
FWS’s determinations that gray wolf populations meet the DPS Policy’s discreteness and
significance criteria general y have not been the subject of legal chal enge. Instead, parties have
chal enged FWS’s determination of DPSs’ geographic boundaries.226 The Oregon district court

216 DPS Policy, 61 Fed. Reg. 4722, 4725 (Feb. 7, 1996).
217 Id.
218 Id.
219 Id.; S. Rep. No. 96-151, at 6-7 (1979).
220 61 Fed. Reg. at 4725.
221 See, e.g., 72 Fed. Reg. 6052, 6059 (Feb. 8, 2007); 73 Fed. Reg. 10,514, 10,519-20 (Feb. 27, 2008).
222 See, e.g., 74 Fed. Reg. 15,123, 15,129 (Apr. 2, 2009).
223 See, e.g., 72 Fed. Reg. at 6059-60; 73 Fed. Reg. at 10,520; 74 Fed. Reg. at 15,129.
224 65 Fed. Reg. 43,450, 43,473 (July 13, 2000); 68 Fed. Reg. 15,804, 15,819 (Apr. 1, 2003).
225 Endangered and T hreatened Wildlife and Plants; Designating the Western Great Lakes Population 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 T hreatened Wildlife, 71 Fed. Reg. 15,266, 15,273-74 (Mar. 27, 2006); 72 Fed. Reg. at
6059-60.
226 Defenders of Wildlife v. Sec’y, U.S. Dep’t of the Interior, 354 F. Supp. 2d 1156, 1170 -71 (D. Ore. 2005). See also
Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp. 2d 7, 14 (D.D.C. 2008) (declining to reach plaintiff’s argument
regarding the DPS boundaries after finding another argument sufficient to vacate the rule).
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vacated FWS’s rule designating the Western, Eastern, and Southwestern DPSs because it
determined that FWS had inappropriately delineated the DPSs.227 In that 2003 final rule, FWS
had combined the proposed Western Great Lakes DPS and Northeastern DPS into the Eastern
DPS after it did not obtain sufficient evidence of gray wolves inhabiting the Northeast to
designate a DPS.228 The agency also extended each DPS to include surrounding states such that
the historical range of the gray wolf was carved up into DPSs.229 The court determined that FWS
had inverted the DPS Policy’s purpose by combining populations with dramatical y different
statuses into one DPS based on geography.230 The court held that FWS must delineate DPSs
carefully to include only discrete, significant populations that qualify as DPSs and their occupied
ranges.231
The Services’ decisions to list a full species rather than a subspecies or DPS may also affect their
ability to delist the species.232 Most of the chal enges FWS has encountered with gray wolf DPSs
have arisen when the agency has designated DPSs from listed full species for delisting purposes.
Plaintiffs have argued that FWS can only designate a DPS to increase protections—either listing a
DPS of a species or subspecies that is not listed or reclassifying a DPS to endangered if the
species or subspecies is listed as threatened—and therefore can only delist a previously listed
DPS.233 FWS has contended that it has authority to delist a DPS from a listed species or
subspecies based on (1) the statutory definition of species including DPSs and (2) its authority to
review species’ statuses and revise listings pursuant to new determinations or designations.234
FWS has argued that its interpretation enables the flexibility Congress intended to provide the
Services through the DPS category and is consistent with the Act’s purposes by al owing the
Services to direct resources to conserve those species or populations most in need of assistance.235
Courts have concluded that the ESA is ambiguous as to whether FWS may designate and delist a
DPS from a listed species or subspecies.236 District courts had initial y agreed with plaintiffs that
FWS’s interpretation was impermissible because DPSs are a “one-way ratchet” and FWS may
only delist a DPS it had previously listed.237 But the D.C. Circuit reversed the district court’s
opinion in 2017, holding that it is reasonable to interpret the ESA as authorizing FWS to revise a
full species or subspecies listing by designating and removing a DPS from the listed species.238
The D.C. Circuit also concluded, however, that FWS had improperly executed designating and
delisting the Western Great Lakes DPS in the 2011 rule because the agency must consider the
effects of removing the DPS on the status of the listed remnant of the species in its analysis .239
Thus although this decision determined that FWS has the legal authority to designate and delist

227 Defenders of Wildlife, 354 F. Supp. 2d at 1170-71.
228 68 Fed. Reg. at 15,809-10.
229 Id. at 15,818-19; Defenders of Wildlife, 354 F. Supp. 2d at 1172-73.
230 Defenders of Wildlife, 354 F. Supp. 2d at 1170-71.
231 Id. at 1171-73.
232 See, e.g., Defenders of Wildlife v. Zinke, 865 F.3d 585 (D.C. Cir. 2017).
233 See, e.g., Humane Soc’y of the U.S. v. Jewell, 76 F. Supp. 3d 69, 109-12 (D.D.C. 2014); Humane Soc’y of the U.S.
v. Kempthorne, 579 F. Supp. 2d 7, 13 -14 (D.D.C. 2008).
234 See, e.g., 74 Fed. Reg. 15,070, 15,075-76 (Apr. 2, 2009); Humane Soc’y of the U.S. v. Zinke, 865 F.3d 585, 592-94
(D.C. Cir. 2017).
235 Humane Soc’y of the U.S., 865 F.3d at 593.
236 Humane Soc’y of the U.S., 579 F. Supp. 2d at 15-16.
237 See, e.g., Humane Soc’y of the U.S., 76 F. Supp. 3d at 109-25.
238 Humane Soc’y of the U.S., 865 F.3d at 600.
239 Id.
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DPSs from listed species and subspecies, the agency has yet to do so in practice in a way that
survives judicial review.
Experimental Populations
The ESA al ows the Secretary to release specimens of listed species into the wild and designate
the population as an “experimental population” if it is “wholly separate geographical y” from
existing populations of the species.240 Experimental populations may be designated as essential or
nonessential to the conservation of the species.241 An experimental population is protected as a
threatened species even if the species is listed as endangered, al owing the Services to limit which
acts are prohibited with respect to the experimental population.242 Additional y, federal agencies
are not required to enter into Section 7 consultations if their actions are likely to affect only
nonessential experimental populations.243 These more limited protections afforded to
experimental populations reduce the regulatory burden on the local community where the
specimens are released, which may reduce public opposition to introducing (or reintroducing) the
species to the wild in that area.244 The Services must ensure that the released population is
“wholly separate geographical y” from existing populations to qualify as experimental and be
subject to these reduced protections.245
FWS implemented two rules in 1994 establishing experimental populations of gray wolves in
(1) the greater Yel owstone area and (2) central Idaho and southwestern Montana.246 FWS
evaluated whether these populations would be “wholly separate geographical y” based on the
areas occupied by existing gray wolf populations, not where any individual gray wolves—lone
dispersers from the pack—might be found.247 In the rules, FWS stated that it would treat any
individual gray wolves found in the experimental population area as part of that population.248
Farm bureaus, researchers, and conservation groups chal enged this approach.249

240 16 U.S.C. § 1539(j)(1).
241 Id.
242 Id.
243 Id.
244 T he ESA was amended in 1982 to allow the Services to reintroduce listed species and designate them as
experimental populations. Endangered Species Act Amendments, Pub. L. No. 97-304, 96 Stat. 1411 (1982) (codified at
16 U.S.C. § 1539(j)). T hough the Services had preexisting authority to reintroduce listed species, a court, reviewing the
statute’s legislative history, concluded that Congress added this section to address the Services’ frustration with
political opposition to such reintroduction efforts borne from “ industry’s fears experimental populations would halt
development projects.” Wyo. Farm Bureau Fed’n v. Babbitt, 199 F.3d 1224, 1231-32 (10th Cir. 2000) (citing H.R. Rep.
No. 97-567, at 8 (1982)).
245 16 U.S.C. § 1539(j)(1).
246 Endangered and T hreatened Wildlife and Plants; Establishment of a Nonessential Experimental Population of Gray
Wolves in Yellowstone National Park in Wyoming, Idaho, and Montana, 59 Fed. Reg. 60,252, 60,253-54 (Nov. 22,
1994); Endangered and T hreatened Wildlife and Plants; Establishment of a Nonessential Experimental Population of
Gray Wolves in Central Idaho and Southwestern Montana, 59 Fed. Reg. 60,266, 60,267 -69 (Nov. 22, 1994).
247 59 Fed. Reg. at 60,253-54; 59 Fed. Reg. at 60,267-69.
248 59 Fed. Reg. at 60,253-54; 59 Fed. Reg. at 60,267-69.
249 Wyo. Farm Bureau Fed’n v. Babbitt, 987 F. Supp. 1349, 1355 -57 (D. Wyo. 1997).
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A federal district court in Wyoming vacated the rules on three grounds, al centered on FWS’s use
of populations rather than individuals to evaluate geographic separation.250 First, the court held
that FWS’s interpretation was inconsistent with clear congressional intent by potential y lessening
protections for individual members of the species that ventured from protected populations into
the experimental population’s range.251 Second, the court held that the rules conflicted with
FWS’s own regulations, which require that any overlapping experimental and nonexperimental
animals al be treated as endangered under the Act.252 Third, it held that treating al gray wolves in
the experimental area as part of the experimental population, including natural y occurring
wolves who migrated there, effected a de facto delisting of those wolves contrary to the ESA.253
On appeal, the U.S. Court of Appeals for the Tenth Circuit (Tenth Circuit) disagreed. It found that
Congress left the phrase “wholly separate geographical y from nonexperimental populations” to
the Services to interpret.254 Reviewing FWS’s interpretation, the court observed that FWS’s
regulations define the term “population” as a group “in common spatial arrangement.”255 FWS
had relied on this definition to conclude that individual dispersers would never be part of a
“population” and therefore need not be accounted for when assessing geographic separation of
populations.256 The court held that this interpretation was reasonable and consistent with the
Act.257 It pointed to the use of species, subspecies, and DPSs rather than individuals as evidence
that the Act’s purpose is to conserve groups of organisms, not individual specimens.258 Consistent
with that approach, the Tenth Circuit found that FWS reasonably determined the gray wolf’s
current range based on where populations were located rather than where individuals might
disperse.259 Observing that wildlife—particularly wolves— moves, the court concluded that
protecting specimens based on where they are rather than where they came from was a reasonable
enforcement approach.260
The Tenth Circuit also held that the plaintiffs’ contrary interpretation would require FWS to
ensure that no individual specimens might cross between experimental and nonexperimental
populations and would unnecessarily limit FWS’s flexibility and discretion.261 The court
determined that such a restrictive interpretation would prevent FWS from making full use of the
experimental population tool and could hinder the conservation of the species, undermining the
purposes of the Act.262 Accordingly, the Tenth Circuit reversed the district court’s decision,
al owing the central Idaho and greater Yel owstone area experimental populations to remain in
place.263 Pursuant to the court’s opinion, the Services may rely on areas occupied by populations

250 See generally id.
251 Id. at 1373-74.
252 Id. at 1375.
253 Id. at 1375-76.
254 Wyo. Farm Bureau Fed’n v. Babbitt, 199 F.3d 1224, 1234 (10th Cir. 2000).
255 Id.
256 Id.
257 Id. at 1234, 1237.
258 Id. at 1234.
259 Id. at 1234-46.
260 Id. at 1235-36.
261 Id. at 1236-37.
262 Id. at 1237.
263 Id. at 1241.
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rather than individuals to determine whether an experimental population would be “wholly
separate geographical y” as the Act required.
Qualifying as Endangered or Threatened
Determining whether a species qualifies as endangered or threatened for purposes of listing or
delisting requires the Services to examine whether the species is in danger of extinction
(1) currently or in the foreseeable future, (2) in al or a significant portion of its range, and (3) due
to one or more of the five statutory factors categorizing types of threats. Though some
commenters have disagreed with FWS’s analyses of threats under the five statutory factors,264
those analyses have not general y been a focal point in gray wolf litigation except for FWS’s
assessment of state management plans’ adequacy under the five statutory factors.265
“All or a Significant Portion of Its Range”
FWS has had difficulty in successfully interpreting “significant portion of its range”—particularly
the “significant” component—in connection with gray wolf rulemakings. Plaintiffs and
commenters have repeatedly chal enged FWS’s interpretation of “significant portion of its range”
in such rulemakings. Following an adverse court decision,266 FWS currently treats “significant
portion of its range” as an independent basis for listing a species, meaning FWS wil list the
species in all of its range if it finds that the species is endangered or threatened in either (1) al or
(2) a significant portion of its range.267 FWS has successfully defended its interpretation of
“range” by interpreting the phrase to mean current rather than historical range.268 But some courts
have rejected FWS’s interpretation of which portions are “significant.”269 FWS has not yet issued
a revised policy on the meaning of “significant portion of its range” or how it interprets
“significant” in light of the new decisions.270
Interpreting the Terms “Significant” and “Range”
In its 2003 rule, plaintiffs chal enged FWS’s interpretation of “significant” using the current
“range” of the species. FWS had used the gray wolf’s current range (i.e., the areas occupied by
the Western Great Lakes and Northern Rocky Mountain populations) as the “significant” areas
when reclassifying the Eastern DPS and Western DPS as threatened.271 An Oregon district court
held that FWS failed to adequately justify why the areas occupied by these populations were the
only “significant” ones.272 The court determined that FWS had instead relied on the gray wolf’s

264 76 Fed. Reg. 81,666, 81,682 (Dec. 28, 2011).
265 Challenges to FWS’s approval of state management plans, which may be analyzed in delisting rules as part of the
factor addressing adequate regulatory mechanisms, are discussed in the “ Recovery and Delisting” section.
266 Defenders of Wildlife v. Salazar, 729 F. Supp. 2d 1207, 1217-28 (D. Mont. 2010).
267 77 Fed. Reg. 55,530, 55,601 (Sept. 10, 2012).
268 See, e.g., Humane Soc’y of U.S. v. Zinke, 865 F.3d 85, 603-04 (D.C. Cir. 2017).
269 Ctr. for Biological Diversity v. Jewell, 248 F. Supp. 3d 946, 956 (D. Ariz. 2017); Desert Survivors v. U.S. Dep’t of
the Interior, 321 F. Supp. 3d 1011, 1073 -74 (N.D. Cal. 2018) (order granting summary judgment to plaintiffs).
270 84 Fed. Reg. 9648, 9684 (Mar. 15, 2019) (interpreting “significant” for purposes of this rulemaking only).
271 Defenders of Wildlife v. Sec’y, U.S. Dep’t of Interior, 354 F. Supp. 2d 1156, 1165 -66 (D. Ore. 2005).
272 Id. at 1167-69.
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current range, without considering the areas where the gray wolf “is no longer viable but once
was.”273 Based in part on this conclusion, the court vacated the rule and remanded it to FWS.274
On remand, FWS revisited its interpretation of the terms “range” and “significant” in its 2007
Western Great Lakes DPS rule:
 Interpreting “Range.” FWS explicitly interpreted “range” to refer to the
species’ current rather than historical range.275 FWS based its interpretation on
the fact that the ESA defines an endangered species or threatened species as one
that “is in danger of extinction” at the time or in the foreseeable future.276 FWS
determined that while a species may be extinct in its historical range, it could
only be in danger of extinction in al or part of its current range.277 The District of
Columbia district court vacated this rule on other grounds,278 but the D.C. Circuit
subsequently upheld FWS’s interpretation of range as reasonable.279 FWS has
since clarified that although it evaluates the current rather than historical range
for purposes of determining the species’ status, it considers the effect of losing
the species’ historical range when evaluating the statutory factors in listing
decisions.280
 Interpreting “Significant.” FWS explained in the 2007 rule that it would
determine what constituted a “significant” part of a species range on a case-by-
case basis depending on the biological needs of the species.281 To conduct this
analysis, FWS would consider the ecosystems on which the species depends and
the values identified in the Act.282 Relevant factors might include the quality and
quantity of habitat, the historical and current use of the habitat, specific uses for
the habitat such as breeding or migration, and the role of that part of the range in
maintaining genetic diversity.283 Though a federal district court in the District of
Columbia subsequently vacated this rule, it did so on other grounds without
reviewing FWS’s interpretation of “significant.”284 The Solicitor’s Office of the
Department of the Interior issued an opinion soon after the final rule affirming
FWS’s interpretation and providing a more extensive explanation of the
position.285 FWS relied on this interpretation and the Solicitor’s opinion in
subsequent gray wolf rulemakings.286

273 Id. at 1167-69.
274 Id. at 1169, 1174.
275 72 Fed. Reg. 6052, 6069 (Feb. 8, 2007).
276 Id. at 6069-70 (emphasis added).
277 Id.
278 Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp. 2d 7 (D.D.C. 2008).
279 See, e.g., Humane Soc’y of U.S. v. Zinke, 865 F.3d 85, 603-04 (D.C. Cir. 2017).
280 See, e.g., 84 Fed. Reg. 9648, 9658 (Mar. 15, 2019).
281 72 Fed. Reg. at 6070-71.
282 Id.
283 Id.
284 Humane Soc’y of the U.S. v. Kempthorne, 579 F. Supp. 2d 7 (D.D.C. 2008).
285 The Meaning of “In Danger of Extinction Throughout All or a Significant Portion of Its Range,” OFFICE OF THE
SOLICITOR, U.S. DEP ’T OF THE INTERIOR (Mar. 16, 2007).
286 73 Fed. Reg. 10,514, 10,533 (Feb. 27, 2008); 74 Fed. Reg. 15,123, 15,152 -53 (Apr. 2, 2009); 74 Fed. Reg. 15,070,
15,089-90 (Apr. 2, 2009).
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Beginning with its 2011 Western Great Lakes DPS rule, FWS adjusted its explanation of
“significant portion of its range” to incorporate principles of conservation biology. The agency
interpreted the phrase to mean that the area is (1) within the current range of the species and
(2) “important to the conservation of the species because it contributes meaningfully to the
representation, resiliency, or redundancy of the species.”287 An area would “contribute[]
meaningfully” if loss of the area would negatively affect FWS’s ability to conserve the species.288
In 2014, the Services issued a joint policy on their interpretation of “significant portion of its
range” under the ESA.289 The policy was general y consistent with FWS’s and the Solicitor’s past
interpretations but contained a revised definition of “significant”:
A portion of the range of a species is “significant” if the species is not currently endangered
or threatened throughout all of its range, but the portion’s contribution to the viability of
the species is so important that, without the members in that portion, the species would be
in danger of extinction, or likely to become so in the foreseeable future, throughout all of
its range.290
District courts later invalidated this definition, concluding that a species could never be listed
based on a “significant portion of its range” under this interpretation, and prohibited the Services
from applying it.291 These courts maintained that under this definition no species could be
endangered or threatened in a significant portion of its range without being endangered or
threatened in al its range.292 The courts reasoned that if a species were endangered or threatened
in a “significant portion” of its range and would be endangered or threatened in al of its range
without that portion, then the species would be listable as endangered or threatened in all its
range.293 In its 2019 proposed rule to delist the remaining gray wolf entities, FWS acknowledged
that the policy had been invalidated and addressed the courts’ opinions by reviewing the gray
wolf’s range to identify any portion “that could be significant under any reasonable definition of
‘significant’ that relates to the conservation of the gray wolf entity.”294 The Services have not yet
issued a revised policy interpreting the phrase “significant portion of its range.”
Using “Significant Portion of Its Range” for Listing
Plaintiffs have also chal enged FWS’s interpretation of “significant portion of its range” to al ow
FWS to list a species only in those parts of its range where it is endangered or threatened. In its
2009 rule designating the Northern Rocky Mountain DPS and delisting it except in Wyoming,
FWS implicitly interpreted the ESA as al owing the agency to list a species only in that portion of
its range where FWS determined the species was endangered or threatened.295 This interpretation
al owed FWS to keep the DPS listed in Wyoming (based on inadequate regulatory mechanisms)

287 76 Fed. Reg. 81,666, 81,722 (Dec. 28, 2011). See also 77 Fed. Reg. 55,530, 55,601-02 (Sept. 10, 2012).
288 76 Fed. Reg. 81,666, 81,722 (Dec. 28, 2011). See also 77 Fed. Reg. 55,530, 55,601-02 (Sept. 10, 2012).
289 Final Policy on Interpretation of the Phrase “Significant Portion of Its Range” in the Endangered Species Act’s
Definition of “Endangered Species” and “T hreatened Species,” 79 Fed. Reg. 37,578 (July 1, 2014).
290 Id. at 37,609.
291 E.g., Desert Survivors v. U.S. Dep’t of the Interior, 321 F. Supp. 3d 1011, 1073 -74 (N.D. Cal. 2018) (order granting
summary judgment to plaintiffs); Ctr. for Biological Diversity v. Jewell, 248 F. Supp. 3d 946, 956 (D. Ariz. 2017).
292 Ctr. for Biological Diversity, 248 F. Supp. 3d at 956.
293 Id.; see also Desert Survivors, 321 F. Supp. 3d at 1073-74 (order granting summary judgment to plaintiffs).
294 84 Fed. Reg. 9648, 9684 (Mar. 15, 2019).
295 74 Fed. Reg. at 15,184.
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but delist it elsewhere.296 A Montana district court vacated this rule on the grounds that FWS’s
interpretation was inconsistent with the ESA and its legislative history.297 The court determined
that Congress added the phrase “significant portion of its range” to expand the circumstances
under which the Services could list a species to address concerns that the ESA’s predecessors
limited the Services to listing species that were endangered worldwide.298 The court accordingly
concluded that the phrase was added to change “when a species can be listed,” not “what must be
listed and protected.”299 The court also concluded that FWS’s interpretation rendered superfluous
DPSs and the vertebrate distinction for DPSs if the agency could limit its listing of a species to
the part of its range that was endangered or threatened.300 The court held that “significant part of
its range” refers to whether, not where, a species is endangered or threatened.301 In light of the
court’s decision, FWS has subsequently interpreted this phrase to constitute an independent basis
for listing a species throughout its range.302
Foreseeable Future
To determine whether a species is threatened, the Services must determine whether it is in danger
of extinction in the “foreseeable future.” Though FWS’s interpretation of this phrase has not been
the focus of legal chal enges to rules relating to the gray wolf, FWS’s interpretation of the term as
it applies to the gray wolf has changed over time. Original y, FWS used the term “foreseeable
future” in its analyses but did not interpret it in general or with respect to the gray wolf
specifical y.303 In the 2007 Western Great Lakes DPS rule, however, FWS defined the term
“foreseeable future” specifical y for the gray wolf.304 The agency determined that 30 years was an
appropriate measure of the foreseeable future for the gray wolf because wolves have 3-year
generations, so 30 years represented 10 generations of wolves.305 FWS viewed 10 generations as
a reasonable period to reliably predict the effects of threats on the species.306
FWS changed course again in the 2009 rules designating and delisting the Western Great Lakes
DPS and Northern Rocky Mountain DPS.307 Rather than defining the “foreseeable future” for the
species as a whole based on its reproductive patterns, FWS announced that it would determine the
foreseeable future for each threat it considered based on its ability to project and predict effects of
the threats reliably.308 For example, the agency used 30 years as the timeframe for available
habitat and distribution models, but when considering the effect of genetic isolation on the
species, it used a model that predicted those effects for the next 100 years.309 Though FWS’s gray
wolf rules have not been overturned based on its interpretation of “foreseeable future,” its

296Id.
297 Defenders of Wildlife v. Salazar, 729 F. Supp. 2d 1207, 1217-28 (D. Mont. 2010).
298 Id. at 1227-28.
299 Id. (emphasis in original).
300 Id. at 1224-25.
301 Id. at 1227.
302 See, e.g., 77 Fed. Reg. 55,530, 55,601 (Sept. 10, 2012).
303 See, e.g., 68 Fed. Reg. 15,804 (Apr. 1, 2003).
304 72 Fed. Reg. 6052, 6069 (Feb. 8, 2007).
305 Id.
306 Id.
307 74 Fed. Reg. 15,070, 15,088-89 (Apr. 2, 2009); 74 Fed. Reg. 15,123, 15,147, 15,156 -57 (Apr. 2, 2009).
308 74 Fed. Reg. at 15,088-89; 74 Fed. Reg. at 15,147, 15,156-57.
309 74 Fed. Reg. at 15,147, 15,156-57.
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approach is information as interpretations of this term have generated chal enges for rules on
other species.310
The Services’ 2019 revisions to their ESA regulations codify an interpretation of “foreseeable
future” much like the one FWS adopted in the 2009 rules.311 As revised, the Services interpret
“foreseeable future” to “extend[] only so far into the future as the Services can reasonably
determine that both the future threats and the species responses to those threats are likely.”312 The
Services intend to evaluate “foreseeable future” on a case-by-case basis based on “considerations
such as the species’ life-history characteristics, threat-projection timeframes, and environmental
variability.”313 Consistent with the approach adopted in the 2009 gray wolf rules, the Services
state that they need not identify the foreseeable future as a specific time period.314
Recovery and Delisting
The Services delist species using the same process they use to list species:315 They evaluate
whether the species meets the definition of “endangered species” or “threatened species” due to
one or more of the five statutory factors based on the best available scientific and commercial
data.316 However, when delisting a species, the Services also general y evaluate the species’
recovery pursuant to any identified objective recovery criteria in recovery plans and assesses the
adequacy of state management plans following delisting.317 FWS has stated that a species need
not meet al of the recovery criteria to be delisted.318 But a Montana district court has required
FWS to provide an adequate explanation if it chooses to reject recovery criteria or delist a species
that has not met these criteria,319 because FWS develops the recovery criteria pursuant to the
statutory directive to establish “objective, measurable criteria which, when met, would result in a
determination ... that the species be removed from the list.”320 State management plans fal under
the purview of “inadequate regulatory mechanisms” in the five-factor analysis, but the Services
give them particular attention in delisting rules because the regulatory mechanisms protecting a
species necessarily change when it is delisted and no longer receives federal protection under the
ESA. Accordingly, this section focuses specifical y on two aspects of recovery and delisting
species: (1) how FWS has addressed objective recovery criteria and (2) post-delisting state
management plans.
Objective Recovery Criteria in Recovery Plans
Plaintiffs have chal enged how FWS has used recovery plan criteria when assessing the gray
wolf’s recovery in its delisting rules. The ESA directs the Services to develop and implement

310 See, e.g., In re Polar Bear Endangered Species Act Listing and Section 4(d) Rule Litigation, 709 F.3d 1, 15 -16 (D.C.
Cir. 2013).
311 84 Fed. Reg. 45,020, 45,020-21 (Aug. 27, 2019) (codified at 50 C.F.R. § 424.11(d)).
312 Id.
313 Id.
314 Id.
315 16 U.S.C. § 1533(c).
316 Id. § 1533(a) & (b).
317 See, e.g., 72 Fed. Reg. 6052, 6052-56, 6083-95 (Feb. 8, 2007); 74 Fed. Reg. 15,123, 15,130-38, 15,166-75 (Apr. 2,
2009).
318 Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160, 1169 (D. Mont. 2008).
319 Defenders of Wildlife, 565 F. Supp. 2d at 1168.
320 16 U.S.C. § 1533(f)(1)(B)(ii) (emphasis added).
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recovery plans for the conservation and survival of listed species if such a plan would promote
conservation of the species.321 In any such plan, the Services must include “objective, measurable
criteria” that, if met, would cause the Services to delist the species.322 The Act, however, directs
the Services to determine whether a species should be reclassified or removed from the list during
a status review based on the Section 4(a) and (b) criteria—namely the endangered and threatened
species definitions and the five statutory categories of threats as determined using the best
available commercial and scientific data—without mentioning recovery plan criteria.323 Though
these two provisions do not inherently conflict, they have generated questions about the role of
objective criteria in recovery plans when delisting species.
Parties have chal enged FWS’s decision to delist a species when it had not met al of the objective
recovery criteria. For example, plaintiffs chal enged the 2008 rule to designate and delist the
Northern Rocky Mountain DPS based in part on a study finding no evidence of genetic exchange
between the greater Yel owstone area population and the other two recovery areas.324 The 1994
EIS included as a recovery criterion that the northern Rocky Mountain recovery areas have
“[t]hirty or more breeding pairs comprising some 300+ wolves in a metapopulation (a population
that exists as partial y isolated sets of subpopulations) with genetic exchange between
subpopulations.”325 The plaintiffs argued—and a Montana district court agreed—that this
criterion required evidence of actual DNA exchange, not just the potential for genetic exchange or
expectation of such exchange in the future.326 The court held that although the ESA did not
prohibit FWS from finding that a species had recovered without meeting recovery criteria, FWS
stil needed to justify adequately rejecting its own recovery criteria to avoid violating the APA.327
FWS addressed these criticisms in its 2009 Northern Rocky Mountain DPS rule in multiple ways.
The agency chal enged the factual conclusion that genetic exchange had not occurred by
questioning the assumptions of the underlying scientific study and identifying new studies
showing wolf dispersal and genetic exchange.328 FWS further explained its interpretation of the
recovery criterion, maintaining that the recovery criterion did not require confirmed genetic
exchange and that genetic exchange need not result from natural migration and could be human-
assisted.329 Final y, the agency explained why the criterion was not needed to find recovery,
reasoning that genetic exchange was not a concern for the populations due to the high level of
preexisting genetic diversity.330 In later rulemakings, FWS has stated that “recovery may be
achieved without al recovery criteria being fully met.”331 When there are questions about whether
a species FWS seeks to delist has met objective recovery criteria, the agency may use one or more
of the following approaches based on past practice: (1) explaining flaws in evidence showing the
criteria have not been met; (2) finding additional evidence supporting its position; (3) explaining

321 16 U.S.C. §1533(f).
322 Id. §1533(f)(1)(B)(2).
323 Id. § 1533(c)(2).
324 Defenders of Wildlife, 565 F. Supp. 2d at 1168.
325 Id.
326 Id. at 1168-69.
327 Id. at 1170.
328 74 Fed. Reg. 15,123, 15,130-35 (Apr. 2, 2009).
329 Id.
330 Id.
331 84 Fed. Reg. 9648, 9657 (Mar. 15, 2019).
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its understanding of the recovery criteria to explain why they have been met; or (4) explaining
why it views the species as having recovered despite not explicitly meeting the objective criteria.
Final y, parties have chal enged the recovery criteria in comments on proposed rules as either
excessive or inadequate to determine whether the species had recovered.332 FWS general y has
concluded that its recovery criteria are adequate,333 and, to date, courts general y have not
addressed FWS’s technical expertise in selecting the criteria.
State Management Plans
State plans for managing a species post-delisting can enter into the Services’ delisting
determinations in two ways: (1) the Services examine any state management plans under “Factor
D: The Inadequacy of Existing Regulatory Mechanisms,”334 and (2) the Services may require in
the recovery plan that they approve certain state management plans before delisting the species.335
For the gray wolf, the Eastern Timber Wolf Recovery Plan required as part of its recovery criteria
that Minnesota, Michigan, and Wisconsin have in place state management plans FWS had
approved as providing adequate wolf protection and management.336 Similarly, the Northern
Rocky Mountain Gray Wolf Recovery Plan required in its recovery criteria that Montana,
Wyoming, and Idaho have FWS-approved state management plans.337 To meet this recovery plan
requirement, (1) the state must create a management plan that FWS approves, (2) FWS must
adequately explain why it approved the plan, and (3) the state must implement the plan.338 The
state or FWS failing to complete any of these steps has delayed FWS delisting gray wolf
populations and caused courts to vacate final delisting rules.339
Formulating an Adequate Management Plan. First, the state must craft a management plan that
FWS deems adequate to ensure the continued recovery of the species. In 2003, FWS designated
but did not delist the Western DPS because the agency had rejected Wyoming’s state management
plan as inadequate. Wyoming chal enged FWS’s decision to not approve its management plan,
but a Wyoming district court dismissed the case for failing to tie the decision to any final agency
action that could be reviewed.340 FWS took a different approach in 2009 when it delisted the
Northern Rocky Mountain DPS without Wyoming because it determined that the Wyoming plan
remained inadequate and could not be approved.341 But a Montana district court determined that
FWS could not delist the DPS only in part, effectively holding that Wyoming must enact an
approved state management plan for the entire DPS to be delisted.342 Congress superseded this

332 See, e.g., 72 Fed. Reg. 6052, 6066 (Feb. 8, 2007) (“T he 1992 Service Recovery Plan is outdated, and its recovery
criteria cannot be used to justify delisting.”).
333 See, e.g., 72 Fed. Reg. at 6066.
334 See, e.g., 76 Fed. Reg. 81,666, 81,701-16 (Dec. 28, 2011); 74 Fed. Reg. 15,070, 15,103-17 (Apr. 2, 2009).
335 See 65 Fed. Reg. 43,450, 43,468, 43,475 (July 13, 2000).
336 Id. at 43,475.
337 Northern Rocky Mountain Wolf Recovery Plan, U.S. FISH & WILDLIFE SERV. at 32 (1987).
338 See, e.g. 65 Fed. Reg. at 43,475; Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160, 1163 (D. Mont. 2008); 74
Fed. Reg. 15,123, 15,123 (Apr. 2, 2009).
339 See, e.g. 65 Fed. Reg. at 43,475; Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160, 1163 (D. Mo nt. 2008); 74
Fed. Reg. 15,123, 15,123 (Apr. 2, 2009).
340 Wyoming v. U.S. Dep’t of the Interior, 360 F. Supp. 2d 1214 (D. Wyo. 2005).
341 74 Fed. Reg. at 15,123, 15,170-72.
342 Defenders of Wildlife v. Salazar, 729 F. Supp. 2d 1207, 1217-28 (D. Mont. 2010).
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decision by enacting legislation in 2011 that directed FWS to reinstate the rule delisting the DPS
except for Wyoming.343
Explaining the Agency’s Approval of the Management Plan. Second, FWS must adequately
explain why it approved the state plan. In 2008, FWS delisted the Northern Rocky Mountain DPS
after Wyoming revised its state management plan between the proposed and final rules.344 FWS
proposed to delist the DPS only if Wyoming modified its plan to provide adequate protection for
the species.345 Wyoming modified its statutes and wolf management plan after the proposed rule
was published.346 In the final rule, FWS determined that the revised plan was adequate to ensure
the gray wolf’s continued recovery.347 A Montana district court, however, held that FWS’s
approval of Wyoming’s plan was likely arbitrary and capricious and issued a preliminary
injunction staying the delisting rule.348 The court determined that the plan suffered from the same
flaws that FWS had identified in the plan it previously rejected and that FWS had failed to
adequately explain why the plan was now sufficient.349 Several months after issuing the
preliminary injunction, the court vacated and remanded the rule at FWS’s request.350
Implementing the Management Plan. Final y, the state must enact and otherwise implement, as
applicable, the approved management plan to ensure that the protections the Services rely on to
delist the species are actual y in place. For example, FWS stated in its 2000 proposed rule that it
had intended to propose delisting the Western Great Lakes DPS as wel as designating it but that
the agency could not because the Minnesota legislature had failed to vote on the plan FWS had
approved before FWS published its proposed rule.351 FWS accordingly proposed to designate the
DPS but not delist it because the recovery criteria were not met without an approved Minnesota
management plan in place.352 Once Minnesota enacted its plan, FWS moved forward with
delisting the DPS (though courts ultimately vacated al the rules that followed).353 Similarly, FWS
found Wyoming’s management plan to be inadequate in the 2007 Northern Rocky Mountain DPS
proposed rule because state laws and regulations prevented the Wyoming Game and Fish

343 Pub. L. No. 112-10, § 1713, 125 Stat. 150 (2011).
344 73 Fed. Reg. 10,514, 10,514, 10,549-50 (Feb. 27, 2008).
345 72 Fed. Reg. 6106, 6106, 6129-31 (Feb. 8, 2007). FWS decided that Wyoming’s existing plan was inadequate
because, among other things, it designated the gray wolf as a predatory animal throughout the state outside the national
parks that could be killed at any time by any means so long as there were at least 15 packs in the state or 7 packs
outside the national parks. Id. at 6129. In the event these criteria were not met , the plan directed the Wyoming Game
and Fish Commission to select areas in the state wh ere the gray wolf would be designated as trophy game subject to
regulated take. Id. FWS determined that this plan did not ensure a sufficient number of breeding pairs would be
maintained in the state. Id. at 6129-30.
346 72 Fed. Reg. 36,939, 36,940 (July 6, 2007). Wyoming revised its statutes and wolf management plan to designate
the gray wolf as trophy game in those parts of the state FWS had identified as significant and committed to maintaining
7 breeding pairs outside the national parks, recognizing Wyoming does not have jurisdiction over the national parks
and assuming that 8 breeding pairs would be maintained there. Id.
347 73 Fed. Reg. 10,514, 10,549 (Feb. 27, 2008).
348 Defenders of Wildlife v. Hall, 565 F. Supp. 2d 1160, 1172 -75 (D. Mont. 2008).
349 Defenders of Wildlife, 565 F. Supp. 2d at 1172-75.
350 73 Fed. Reg. 75,356, 75,357 (Dec. 11, 2008).
351 65 Fed. Reg. 43,450, 43,468, 43,475 (July 13, 2000).
352 Id.
353 See, e.g., 73 Fed. Reg. at 10,547-48; 74 Fed. Reg. 15,070, 15,103-05 (Apr. 2, 2009).
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The Gray Wolf: A Case Study in Endangered Species Act Listing Challenges

Commission from actual y implementing certain components of the plan.354 Once Wyoming
modified its state laws and regulations, FWS approved the plan.355
As the litigation over the FWS’s 2012 rule il ustrates, although states must enact management
plans for the Services to move forward with delisting a species, the regulatory mechanisms need
not al be legal y binding so long as states assure the Services that adequate protections wil be
provided in practice. The federal district court for the District of Columbia vacated FWS’s 2012
rule delisting the gray wolf in Wyoming because FWS relied on nonbinding promises from
Wyoming that it would manage the population above the minimum recovery level.356 On appeal,
the D.C. Circuit reversed the district court and restored the rule delisting the gray wolf in
Wyoming, holding that “regulatory mechanisms” need not be binding with the force of law for
FWS to determine they were adequate to protect the species.357
The Services’ approval of state management plans and the adequacy of their explanations for
approving the plans can accordingly play a central role in both finalizing delisting rules and
surviving judicial review of those rules. For a particular species and state, the adequacy of the
state’s regulatory mechanisms and management plan are determined on a case-by-case basis
through negotiation between the state and the Services.
Conclusion
The history of the gray wolf under the ESA il ustrates the chal enges FWS has faced in
conserving the species as the Act intended. In implementing the ESA, the Services must contend
with disagreements over how to interpret ambiguous terms, uncertain and ever-changing
scientific data, and conflicting views on what it means to conserve species and the role of the
states in that effort. These issues can complicate the Services’ efforts to conserve endangered and
threatened species and delist them, consistent with the Act’s purposes.
Difficulties that delay delisting species may frustrate certain stakeholders, such as state wildlife
agencies that want more flexibility in managing the species or private entities in the species’
habitat who must comply with the Act’s prohibitions and Section 7 consultation requirements.
Other stakeholders such as conservation groups or animal rights activists may raise concerns that
species are inadequately regulated to ensure their long-term recovery or continued biodiversity
due to uncertainties in the science and ambiguities in the statute. Either set of stakeholders may
question whether the Act is effectively promoting the recovery of listed species.
In light of the scientific and administrative chal enges FWS has encountered with regulating the
gray wolf under the Act, Congress could consider amending the Act to address these issues and
ensure the Act is implemented in accordance with congressional intent. Such legislation could
amend the Act general y or specifical y with respect to a particular action, such as the Act
directing FWS to reinstate the rule designating and delisting the Northern Rocky Mountain DPS

354 72 Fed. Reg. 6106, 6106, 6129-31 (Feb. 8, 2007).
355 73 Fed. Reg. at 10,514, 10549-50. A court subsequently vacated this rule after determining that FWS was acted in
an arbitrary and capricious manner in approving the Wyoming wolf management plan because it suffered from the
same flaws as the 2003 plan FWS rejected. Defenders of Wildlife, 565 F. Supp. 2d at 1172-75. Wyoming revised its
wolf management plan yet again and FWS ultimately delisted the gray wolf in Wyoming in 2012. 77 Fed. Reg. 55,530
(Sept. 10, 2012).
356 Defenders of Wildlife v. Jewell, 68 F. Supp. 3d 193, 196, 203-10 (D.D.C. 2014).
357 Defenders of Wildlife v. Zinke, 849 F.3d 1077, 1082-88 (D.C. Cir. 2017).
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except for Wyoming.358 Legislative proposals introduced in the 116th Congress would pursue
each of these approaches: amending the Act generally359 or specifical y directing FWS to issue
new rules or reissue vacated ones regarding the gray wolf.360

358 Department of Defense and Full-Year Appropriations Act, 2011, Pub. L. No. 112-10, § 1713, 125 Stat. 150 (2011).
359 See, e.g., S. 1429, 116th Cong. (2019); S. 2343, 116th Cong. (2019); S. 2491, 116th Cong. (2019); H.R. 2245, 116th
Cong. (2019); H.R. 5095, 116th Cong. (2019); H.R. 4804, 116th Cong. (2019).
360 See, e.g., S. 831, 116th Cong. (2019) (directing the Department of the Interior to reinstate the final rule designating
and delisting the Western Great Lakes DPS and precluding judicial review of that rule or the reinstated rule delisting
the gray wolf in Wyoming); American Wild Game and Livestock Protection Act, S. 3140, 116th Cong. (2019)
(directing the Secretary of the Interior to issue a final rule delisting the gray wolf); Gray Wolf State Management Act of
2019, H.R. 4494, 116th Cong. (2019) (directing the Secretary of the Interior to reissue the final rule designating and
delisting the Western Great Lakes DPS).
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Appendix. Timeline
Table A-1. Gray Wolf Endangered Species Act Timeline
Key Legislative, Regulatory, and Litigation Developments
Date
Event
Description
Oct. 15, 1966
Legislation
Endangered Species Preservation Act enacted
March 11, 1967
Listing
Timber wolf listed as endangered
Dec. 5, 1969
Legislation
Endangered Species Conservation Act enacted, amending Endangered
Species Preservation Act
June 4, 1973
Listing
Northern Rocky Mountain wolf listed as endangered
Dec. 28, 1973
Legislation
Endangered Species Act enacted, replacing Endangered Species
Preservation Act
Apr. 21, 1975
Listing
Mexican wolf listed as endangered
July 1, 1975
Legislation
Convention on International Trade in Endangered Species of Wild Fauna
and Flora (CITES) entered into force
June 14, 1976
Listing
Gray wolf listed as endangered in Texas, New Mexico, and Mexico
pursuant to CITES
March 9, 1978
Reclassification
Timber wolf, northern Rocky Mountain wolf, Mexican wolf, and Texas gray
wolf reclassified as subspecies of the gray wolf;
Gray wolf listed as endangered in 48 coterminous states excluding
Minnesota and in Mexico;
Gray wolf listed as threatened in Minnesota with special 4(d) rule al owing
take for depredation control;
Critical habitat established in Minnesota and Michigan
June 5, 1978
Regulation
Approved recovery plan for the eastern timber wolf
Aug. 10, 1983
Regulation
Special 4(d) rule for gray wolf in Minnesota expanded to address
depredation
Jan. 5, 1984
Court decision
Minnesota district court vacated special 4(d) rule for gray wolf in
Minnesota
Feb. 19, 1985
Court decision
Eighth Circuit affirmed in part and remanded in part Montana district court
decision vacating special 4(d) rule for gray wolf in Minnesota and remanded
to district court
May 2, 1985
Court decision
District court orders amendments to special 4(d) rule for gray wolf in
Minnesota
Dec. 12, 1985
Regulation
Special 4(d) rule for gray wolf in Minnesota amended consistent with court
orders
Apr. 24, 1989
Petition denied
Petition to delist gray wolf denied as not warranted
Nov. 30, 1990
Petition denied
Petition to delist gray wolf denied as not warranted
Jan. 31, 1992
Regulation
Approved revised recovery plan for the eastern timber wolf
Nov. 22, 1994
Experimental
Nonessential experimental population of gray wolves established in
population
Yel owstone National Park in Wyoming, Idaho, and Montana
Jan. 12 & 14,
Experimental
Gray wolves released in Yel owstone National Park and central Idaho
1995
population
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Date
Event
Description
Dec. 12, 1997
Court decision
Wyoming district court vacated wolf introduction rule and ordered
introduced wolves removed
Jan. 12, 1998
Experimental
Nonessential experimental population of Mexican gray wolves established
population
in Arizona and New Mexico
Oct. 19, 1998
Petition denied
Petition to delist gray wolf in Minnesota, Wisconsin, and Michigan denied as
not warranted
Jan. 13, 2000
Court decision
Tenth Circuit reverses district court and reinstates rule establishing
experimental population in Yel owstone National Park and central Idaho
Apr. 1, 2003
Reclassification
Established three DPSs of the gray wolf: Western DPS, Eastern DPS, and
DPS
Southwestern DPS;
Regulation
Reclassified Western DPS and Eastern DPS from endangered to
threatened;
Implemented special 4(d) rule for Western DPS and Eastern DPS
Jan. 6, 2005
Regulation
Implemented regulations for nonessential experimental population in
Yel owstone National Park and central Idaho within Western DPS to al ow
more flexibility in state and tribal management
Jan. 31, 2005
Court decision
Oregon district court vacated the rule reclassifying Western DPS and
Eastern DPS from endangered to threatened
March 18, 2005
Court decision
Wyoming district court dismissed case by State of Wyoming chal enging
FWS’s rejection of its gray wolf management plan
Aug. 19, 2005
Court decision
Vermont district court also vacated the rule reclassifying Western DPS and
Eastern DPS from endangered to threatened
Oct. 26, 2005
Petition may be
Petition to establish Northern Rocky Mountain DPS and delist it may be
warranted
warranted
Dec. 9, 2005
Petition denied
Petition to delist gray wolf in Nevada denied as not warranted
Aug. 1, 2006
Petition denied
Petition to establish northern Rocky Mountain DPS and delist it denied as
not warranted in 12-month finding based on inadequate protections under
Wyoming state law
Feb. 8, 2007
DPS
Established the Western Great Lakes DPS and delisted it
Delisting
Jan. 28, 2008
Regulation
Implemented revised regulations for nonessential experimental population
in Yel owstone National Park and central Idaho within Western DPS to
al ow more flexibility in state and tribal management
Feb. 27, 2008
DPS
Established Northern Rocky Mountain DPS and delisted it
Delisting
July 18, 2008
Court decision
Montana district court issued preliminary injunction reinstating Endangered
Species Act protections for Northern Rocky Mountain DPS pending final
resolution of the matter
Sept. 29, 2008
Court decision
District of Columbia district court vacated the rule establishing the
Western Great Lakes DPS and delisting it
Oct. 14, 2008
Court decision
Montana district court vacated the rule establishing the Northern Rocky
Mountain DPS and delisting it, at the request of FWS
Dec. 11, 2008
Relisting
Reinstated protections of the Endangered Species Act for Northern Rocky
Mountain DPS and Western Great Lakes DPS to comply with court orders
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Date
Event
Description
Apr. 2, 2009
DPS
Established Northern Rocky Mountain DPS and delisted it except for gray
Delisting
wolves in Wyoming, which would continue to be managed as a
nonessential experimental population
Apr. 2, 2009
DPS
Established the Western Great Lakes DPS and delisted it, removing critical
Delisting
habitat in Minnesota and Michigan and special 4(d) regulations for
Minnesota
Sept. 8, 2009
Court decision
Montana district court denies motion for preliminary injunction to prohibit
scheduled wolf hunts but found a likelihood of success on the merits
regarding the rule establishing Northern Rocky Mountain DPS and delisting
it except for Wyoming
Sept. 16, 2009
Relisting
Reinstated protections of Endangered Species Act for Western Great
Lakes DPS to comply with settlement agreement and court order
June 10, 2010
Petition denied
Petition to establish Northeastern United States DPS and list it as
endangered denied as not warranted
Aug. 4, 2010
Petition may be
Petition to reclassify Mexican wolf as a separate subspecies may be
warranted
warranted
Aug. 5, 2010
Court decision
Montana district court vacated the rule establishing the Northern Rocky
Mountain DPS and delisting it except for Wyoming
Sept. 14, 2010
Petition may be
Petition to delist the gray wolf in Minnesota, Wisconsin, and Michigan may
warranted
be warranted
Oct. 26, 2010
Relisting
Reinstated protections of the ESA for the Northern Rocky Mountain DPS
to comply with court order
Nov. 18, 2010
Court decision
Wyoming district court set aside FWS requirement that Wyoming
designate the entire state as a trophy game area to provide adequate
protection for gray wolves upon delisting and remanded to agency to
determine whether Wyoming’s management plan with its proposed trophy
game area constitutes an adequate regulatory mechanism
Apr. 9, 2011
Court decision
Montana district court rejects settlement of suit chal enging delisting of
Northern Rocky Mountain DPS that would have removed ESA protections
in Idaho and Montana
April 15, 2011
Legislation
Department of Defense and Ful -Year Appropriations Act, 2011, directed
the Secretary of the Interior to reinstate rule establishing the Northern
Rocky Mountain DPS and delisting it except for Wyoming
May 5, 2011
Delisting
Reinstated rule establishing the Northern Rocky Mountain DPS and
delisting it except for Wyoming to comply with legislation
Aug. 3, 2011
Court decision
Montana district court upholds constitutionality of legislation directing the
Secretary of the Interior to reinstate the vacated rule establishing the
Northern Rocky Mountain DPS and delisting it except for Wyoming
Dec. 28, 2011
DPS
Designated Western Great Lakes DPS to include wolves in Minnesota,
Delisting
Wisconsin, and Michigan along with portions of adjoining states and
delisted it;
Removed critical habitat in Minnesota and Michigan and special 4(d) rule for
Minnesota
March 14, 2012
Court decision
Ninth Circuit affirmed Montana district court decision upholding
constitutionality of legislation directing the Secretary of the Interior to
reinstate vacated rule establishing the Northern Rocky Mountain DPS and
delisting it except for Wyoming
Sept. 10, 2012
Delisting
Delisted gray wolf in Wyoming and eliminated nonessential experimental
population designation for gray wolves in Yel owstone National Park
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The Gray Wolf: A Case Study in Endangered Species Act Listing Challenges

Date
Event
Description
Oct. 9, 2012
Petition denied
Petition to designate Mexican wolf as subspecies or DPS denied as not
warranted
Sept. 23, 2014
Court decision
District of Columbia district court vacated and remanded rule delisting
gray wolf in Wyoming based on inadequacy of Wyoming regulatory
mechanisms
Dec. 19, 2014
Court decision
District of Columbia district court vacated rule designating the Western
Great Lakes DPS and delisting it on the grounds that FWS could not
simultaneously designate a DPS and delist it
Jan. 16, 2015
Listing
Listed Mexican wolf as endangered subspecies;
Revised regulations for nonessential experimental population of the
Mexican wolf
Feb. 20, 2015
Relisting
Reinstated protections of ESA for gray wolf in Wyoming as nonessential
experimental population and for gray wolf in Western Great Lakes DPS as
threatened in Minnesota and endangered in Wisconsin, Michigan, and
portions of adjoining states to comply with court orders
March 3, 2017
Court decision
D.C. Circuit reversed District of Columbia district court and reinstated
rule delisting gray wolf in Wyoming
May 1, 2017
Delisting
Reinstated rule delisting gray wolf in Wyoming
Aug. 1, 2017
Court decision
D.C. Circuit affirmed District of Columbia district court decision vacating
rule designating Western Great Lakes DPS and delisting it
March 31, 2018
Court decision
Arizona district court remanded rule revising regulations for nonessential
experimental population of the Mexican wolf and retaining that designation
to FWS to consider the conservation of the species in a revised rule
March 15, 2019
Proposed
Proposed delisting gray wolf wherever it is found but maintaining Mexican
delisting
wolf endangered status
Nov. 3, 2020
Delisting
Delisted the gray wolf in the lower 48 states except for Mexican wolf,
which remains listed as endangered
Source: Congressional Research Service.
Note: The actions listed in this table were taken by FWS unless otherwise specified.

Author Information

Erin H. Ward

Legislative Attorney

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The Gray Wolf: A Case Study in Endangered Species Act Listing Challenges

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