7-2020 ENVIRONMENTAL LAW REPORTER 50 ELR 10531
by Jason C. Rylander, Megan Evansen, Jennifer R.B. Miller, and Jacob Malcom
DEFINING HABITAT TO PROMOTE
CONSERVATION UNDER THE ESA
Jason C. Rylander is Senior Endangered Species Counsel with the Defenders of Wildlife. Megan Evansen
is Conservation Science and Policy Analyst with the Center for Conservation Innovation (CCI), Defenders
of Wildlife. Jennifer R.B. Miller is a Senior Scientist at CCI. Jacob Malcom is the Director of CCI.
The U.S. Supreme Court’s opinion in Weyerhaeuser
Co. v. U.S. Fish & Wildlife Service raises important
questions about the scope of the Endangered Spe-
cies Act’s (ESA’s)1 protections for critical habitat.2 Foremost
among them is a question one might think was long set-
tled: what is “habitat”?
Under §4 of the ESA, when a species is listed as threat-
ened or endangered, the U.S. Fish and Wildlife Service
(FWS or the Service) or National Marine Fisheries Service
(NMFS) must also, to the maximum extent practicable,
designate as “critical habitat” those areas deemed “essen-
tial to the conservation of the species.” By “conservation,”
the ESA requires measures necessary to ensure that a listed
species both survives and recovers. e designation of criti-
cal habitat matters because, under §7, federal agencies must
ensure that any action they authorize, fund, or carry out
does not result in the “destruction or adverse modication”
of habitat the agencies have deemed to be “critical.”3
Not surprisingly, this provision has engendered a fair
amount of controversy over the years.4 Most of that con-
troversy has focused on either the denition of “adverse
modication” or whether the designated habitat is essential
to the conservation of the species, a nding that must be
made “on the basis of the best scientic data available and
after taking into consideration the economic impact, the
impact on national security, and any other relevant impact
of specifying any particular area as critical habitat.”5 But
until Weyerhaeuser, no court had ever considered speci-
1. 16 U.S.C. §§1531-1544, ELR Stat. ESA §§2-18.
2. 139 S. Ct. 361, 48 ELR 20196 (2018). [Editor’s Note: Jason Rylander au-
thored an amicus brief in the Supreme Court in the Weyerhaeuser case on
behalf of Defenders of Wildlife, Animal Welfare Institute, Humane Society
of the United States, Sierra Club, and WildEarth Guardians.]
3. 16 U.S.C. §1532(5)(A).
4. Debate over this provision can be found in both legal and scientic litera-
ture. See, e.g., Giord Pinchot Task Force v. U.S. Fish & Wildlife Serv., 378
F.3d 1059, 1070, 34 ELR 20068 (9th Cir. 2004) (requiring FWS to provide
for species recovery, not just survival, in designating critical habitat); see also
Dennis D. Murphy & Barry R. Noon, Exorcising Ambiguity From the En-
dangered Species Act: Critical Habitat as an Example, 8 E S
UPDATE 6 (1991).
5. 16 U.S.C. §1533(b)(2); id. §1533(a)(3)(A), (a)(3)(A)(i).
cally what the word “habitat” actually means as a legal or
Enter the dusky gopher frog, a shy species of frog
endemic to ephemeral ponds and adjacent forested uplands
in Louisiana and Mississippi. Habitat loss—destruction of
those transitory ponds and conversion of longleaf pine for-
ests to loblolly pine plantations—reduced the frog’s range
to a single population in a Mississippi pond. With fewer
than 100 frogs remaining at that site, FWS declared the
species to be endangered in 2001.6
At the time, FWS did not designate critical habitat.
When, following litigation by conservation groups, the
Service nally proposed to designate critical habitat for
the frog, it concluded after peer review that the existing
occupied habitat was not sucient to provide for conserva-
tion and recovery of the species.7 After scouring the frog’s
historic range for habitat that contained the right mix of
ephemeral ponds and forest uplands, the Service desig-
nated an area in Louisiana within the historic range of the
frog that contained some of the last remaining ponds suit-
able for breeding.8 ese uplands, however, were degraded,
and the species had not been seen there since 1965.9
According to FWS, the parcel in question—referred to
as Unit 1—was essential to the conservation of the dusky
gopher frog because it was the last remaining area of the
species’ historic range that could still support the species
in the future.10 According to the property owners, which
include the Weyerhaeuser timber company, the area is not
only unoccupied but uninhabitable without extensive res-
toration eorts. Whether the frog actually could live on
the parcel without restoration is a matter of some debate
6. FWS, Final Rule to List the Mississippi Gopher Frog Distinct Population
Segment of Dusky Gopher Frog as Endangered, 66 Fed. Reg. 62993 (Dec.
7. FWS, Designation of Critical Habitat for Mississippi Gopher Frog, 75 Fed.
Reg. 31387, 31394 (June 3, 2010).
8. FWS, Designation of Critical Habitat for Dusky Gopher Frog, 77 Fed. Reg.
35118 (June 12, 2012).
9. 77 Fed. Reg. at 35131.
10. Id. at 35124 (“[T]he ve ponds in Unit 1 provide breeding habitat that in
its totality is not known to be present elsewhere within the historic range of
the dusky gopher frog.”).
Copyright © 2020 Environmental Law Institute®, Washington, DC. Reprinted with permission from ELR®, http://www.eli.org, 1-800-433-5120.
50 ELR 10532 ENVIRONMENTAL LAW REPORTER 7-2020
in the administrative record.11 But assuming it could not,
the question then arises: can an area be considered “habi-
tat,” let alone “critical habitat,” if a species cannot cur-
rently live there?
In a short ruling, the Weyerhaeuser Court opined that
“critical habitat” must rst be “habitat,” but it did not
attempt to dene exactly what habitat is or how much def-
erence FWS should get on what is both a biological and
policy question. e Court also sidestepped whether cur-
rently unoccupied “habitat” must in fact be “habitable”
at the time of designation as critical habitat. e task of
dening “habitat” now falls to the ESA’s implementing
agencies or to the U.S. Congress.12
It should go without saying that how habitat is ulti-
mately dened has serious implications for species conser-
vation. In the wake of recent reports on the accelerating
loss of biodiversity due largely to habitat loss in the United
States and across the globe, how and where we protect
habitat is vital to preventing extinction and ensuring the
long-term security of species. A denition that is too nar-
row and excludes degraded but restorable habitat, or areas
that are likely to become habitat in the foreseeable future,
could leave areas essential to species recovery unprotected.
It is, however, possible to dene habitat in a way that
is consistent with the intent of the ESA, reects the best
available science, is operationally workable, and also broad
enough to account for species’ needs. is Comment pro-
poses such a denition.
When Congress passed the ESA in 1973, it was acutely
aware that stemming the loss of biodiversity required
more than protecting individual animals and plants; it
also required protecting critical habitat from destruc-
tion or adverse modication.13 Unfortunately, that is as
true today as ever. e recent Intergovernmental Science-
Policy Platform on Biodiversity and Ecosystem Services
(IPBES) report found that as many as one million spe-
cies—one in eight species on earth—face extinction in
the coming decades.14 is is a rate “tens to hundreds of
times higher” than the background rate of extinction.15
Despite signicant eorts to prevent extinction under the
11. Weyerhaeuser Co. v. U.S. Fish & Wildlife Serv., 139 S. Ct. 361, 369, 48
ELR 20196 (2018).
12. After the Weyerhaeuser decision, FWS agreed to withdraw the critical habi-
tat rule, and the parties agreed to dismiss the case. Accordingly, the lower
courts have no present opportunity to consider the denition of habitat in
the rst instance.
13. As the Supreme Court has recognized: “Congress started from the nding
that ‘[the] two major causes of extinction are hunting and destruction of
natural habitat.’ Of these twin threats, Congress was informed that the
greatest was destruction of natural habitats.” Tennessee Valley Auth. v.
Hill, 437 U.S. 153, 179, 8 ELR 20513 (1978) (quoting S. R. N. 93-
307, at 2 (1973), reprinted in 1973 U.S.C.C.A.N. 2989, 2990) (alteration
14. IPBES, S P G A R-
B E S 12 (Sandra Díaz et al.
eds., 2019), https://ipbes.net/sites/default/les/2020-02/ipbes_global_
ESA and other laws, the loss of biodiversity remains a rap-
idly growing crisis.
As the National Academy of Sciences made clear
in a seminal report 25 years ago, “there is no disagree-
ment in the ecological literature about one fundamental
relationship: sucient loss of habitat will lead to species
extinction.”16 Indeed, the IPBES report found habitat loss
remains the leading cause of this extinction crisis, ahead of
direct exploitation, climate change, pollution, and invasive
species.17 Climate change will only exacerbate these trends,
causing some habitats to become inhospitable for some spe-
cies, while currently unsuitable areas may become viable
habitats for species seeking to adapt and survive in a warm-
Recognizing the importance of habitat protection in any
comprehensive scheme to protect imperiled species, Con-
gress designed the ESA to address not only actions directed
at species themselves—such as hunting and trade—but also
to “provide a means whereby the ecosystems upon which
endangered species and threatened species depend may be
conserved.”19 To that end, habitat protection is elemental
to the ESA’s statutory scheme: §4 requires designation of
critical habitat at the time of listing20; §5 explicitly calls
for land conservation21; §7 contains the operative provi-
sions for protecting critical habitat22; §9 prohibits destruc-
tion of habitat that would directly harm a listed species23;
and §10 provides for habitat conservation plans.24 Almost
every part of the Act addresses the need to protect habitat
in order to prevent extinction.
e Act’s critical habitat provisions, however, may be
the most signicant of those habitat protection provi-
sions. In the lead-up to the 1978 amendments, Congress
reemphasized that “[t]he loss of habitat for many species
is universally cited as the major cause for the extinction
of species worldwide.”25 Moreover, Congress specically
stated that “if the protection of endangered and threatened
species depends in large measure on the preservation of
the species’ habitat, then the ultimate eectiveness of the
Endangered Species Act will depend on the designation of
16. N R C, S E S
A 72 (1995).
17. IPBES, supra note 14, at 12-13.
18. Daniel A. Farber, Separated at Birth? Addressing the Twin Crises of Biodiversity
and Climate Change, 42 E L.Q. 841, 846 (2015).
19. 16 U.S.C. §1531(b). “Conservation,” in turn, is statutorily dened as “the
use of all methods and procedures which are necessary to bring any endan-
gered or threatened species to the point at which the measures provided
pursuant to this chapter are no longer necessary.” Id. §1532(3).
20. Id. §1533(a)(3)(A)(i) (requiring, when possible, designation of critical habi-
tat at the time of listing); id. §1534 (providing for land conservation).
21. Id. §1534 (providing for land conservation).
22. Id. §1536(a)(2) (prohibiting destruction or adverse modication of criti-
23. Id. §1538 (prohibiting “harm” to a listed species, which has been dened
by FWS and NMFS as including destruction of habitat that kills or injures
wildlife by impairing essential behavioral patterns); see also Babbitt v. Sweet
Home Chapter of Cmtys. for a Great Or., 515 U.S. 687, 25 ELR 21194
(1995) (requiring a reasonable likelihood of harm to individual animals for
habitat modication to constitute take under the ESA).
24. 16 U.S.C. §1539 (providing for habitat conservation plans).
25. H.R. R. N. 95-1625, at 5 (1978).
26. H.R. R. N. 94-887, at 3 (1976).
Copyright © 2020 Environmental Law Institute®, Washington, DC. Reprinted with permission from ELR®, http://www.eli.org, 1-800-433-5120.
7-2020 ENVIRONMENTAL LAW REPORTER 50 ELR 10533
Consistent with Congress’ understanding that habitat
preservation is the key to recovering species, the ESA rec-
ognizes that critical habitat can be occupied or unoccupied
by the species at the time of listing and provides separate
denitions for each. “Occupied critical habitat” is dened
as “the specic areas within the geographical area occupied
by the species, at the time it is listed ... on which are found
those physical or biological features (I)essential to the con-
servation of the species and (II)which may require special
management consideration or protection.”27
By contrast, the denition of “unoccupied critical habi-
tat” includes the “specic areas outside the geographical
area occupied by the species at the time it is listed ... upon
a determination by the Secretary that such areas are essen-
tial for the conservation of the species.”28 Notably, Con-
gress’ denition of unoccupied critical habitat specically
omits the requirement that such habitat possess the “physi-
cal or biological features” essential to species conservation
and, instead, requires only that FWS (or NMFS) make a
“determination ... that such areas are essential for the con-
servation [(i.e., recovery)] of the species.”29
Congress’ determination that both occupied and unoc-
cupied habitat may be essential to conservation makes
biological and practical sense. When a species with a pre-
viously larger range has been reduced to a small patch of
presently suitable habitat by the “destruction [or] modi-
cation ... of its habitat,” recovery may necessarily require
the protection of both the dwindling areas where the spe-
cies still occurs and other areas needed for its conservation.
at includes historically occupied areas capable of being
restored and recolonized. For such species, designation of
unoccupied critical habitat could play an indispensable role
in their recovery.
For all the emphasis on dening occupied and unoc-
cupied critical habitat, including reference to physical fea-
tures essential to the species’ conservation, it is perhaps
surprising that Congress never dened “habitat” in the
rst instance. But while nearly 50 years have passed since
the ESA was enacted, only now have courts begun to parse
whether lands designated as critical habitat because of their
actual or potential benets to a species might not qualify
II. The Importance of Critical Habitat
Before digging deeper into what habitat means, it is worth
considering why critical habitat matters. Although for
many years FWS downplayed the value of critical habitat
as redundant with the ESA’s take prohibition and generally
tried to avoid designating it,30 critical habitat has impor-
tant benets to species. In 1995, the National Research
Council found that while “ecosystem protection is of para-
27. 16 U.S.C. §1532(5)(A)(i).
28. Id. §1532(5)(A)(ii).
29. Compare 16 U.S.C. §1532(5)(A)(i), with 16 U.S.C. §1532(5)(A)(ii).
30. David J. Hayes et al., A Modest Role for a Bold Term: “Critical Habitat” Un-
der the Endangered Species Act, 43 ELR 10671, 10672 (Aug. 2013) (“Criti-
cal habitat designations typically have modest impacts primarily because
the regulatory consequences of listing a species in the rst place are so
mount importance to species preservation,” the fact that
“nearly 80% of all species listed do not have critical habitat
designations is a cause for concern.”31 Prompted in part by
conservation litigation, FWS has since done an about-face
on the value of critical habitat. Still, only about one-half
of listed species currently have designated critical habitat.32
Critical habitat’s contribution to recovery will, of
course, vary on a species-by-species basis, but research
shows a correlation between critical habitat designation
and positive trends in recovery status.33 Other studies
have shown that designation of critical habitat is “corre-
lated with increased eort to protect species.”34 Species
with critical habitat are also more likely to have recovery
plans that are up-to-date and being implemented than
species without critical habitat.35
For projects on federal lands or that require federal
funding, approval, or implementation, ESA §7 provides
important substantive and procedural checks on actions
aecting critical habitat. Section 7 is particularly impor-
tant for unoccupied critical habitat because there is no
other statutory mechanism for protecting these potentially
vital areas. Although the Act’s take prohibition protects
species from, among other things, “harm,” the regulatory
denition of “harm” only applies to habitat modication
that could actually kill or injure wildlife. at is unlikely
to happen if the listed species is not present.36 By contrast,
the proscription on federal agency actions that may destroy
or adversely modify critical habitat protects designated
areas regardless of whether an action will directly harm
individual animals. us, critical habitat designation pro-
vides an important statutory protection for areas that are
unoccupied but necessary for the expansion and recovery
of the species.
When critical habitat is designated on federal lands, it
can also help prioritize §7(a)(1) conservation eorts. Under
§7(a)(1), all federal agencies must “utilize their authorities
in furtherance of the purposes of [the ESA] by carrying out
programs for the conservation of endangered species and
threatened species.”37 is obligation includes everything
from recovery planning to direct restoration of habitat on
federal lands. Take, for example, the U.S. Forest Service’s
eorts to restore degraded unoccupied critical habitat for
the New Mexico meadow jumping mouse. Unoccupied
31. N R C, supra note 16, at 76, 179.
32. At this writing, according to the ESA box score, FWS and NMFS had
designated critical habitat 853 times for 1,665 domestic species. See FWS,
USFWS reatened & Endangered Species Active Critical Habitat Report,
https://ecos.fws.gov/ecp/report/table/critical-habitat.html (last visited May
33. Martin F.J. Taylor, e Eectiveness of the Endangered Species Act: A Quanti-
tative Analysis, 55 BS 360, 363 (2005).
34. Amy N. Hagen & Karen E. Hodges, Resolving Critical Habitat Designation
Failures: Reconciling Law, Policy, and Biology, 20 C B
399, 400 (2006).
35. Id. (“Critical habitat designation therefore helps populations improve,
increases knowledge about trends, and contributes to recovery goals be-
36. 50 C.F.R. §17.3 (2019); Babbitt v. Sweet Home Chapter of Cmtys. for a
Great Or., 515 U.S. 687, 25 ELR 21194 (1995) (requiring a reasonable
likelihood of harm to individual animals for habitat modication to consti-
tute take under the ESA).
37. 16 U.S.C. §1536(a)(1).
Copyright © 2020 Environmental Law Institute®, Washington, DC. Reprinted with permission from ELR®, http://www.eli.org, 1-800-433-5120.
50 ELR 10534 ENVIRONMENTAL LAW REPORTER 7-2020
critical habitat for this species was designated along ripar-
ian tracts degraded by years of overgrazing.38 Following
this designation, the Forest Service engaged with conserva-
tion partners and local ranchers to install a series of cattle
exclusion fences and alternative water sources that allowed
these degraded areas to return to their natural condition
and once again host the mouse.39
Designation also generates valuable information that
federal, state, local, and private landowners can use to help
conserve species, including the location and importance of
the particular areas that are essential to species recovery.40
e information developed during the designation process
can also help focus the eorts of conservationists, states,
and private landowners when developing habitat conserva-
tion plans. Even where no federal action is involved, these
actors may elect to tailor their activities to avoid negatively
aecting a sensitive area.41 Designation can help maximize
the conservation value of land acquisition by allowing par-
ties to target those areas that would most benet a species.
For example, after conservation groups expressed concern
about development near one of the dusky gopher frog’s last
known breeding ponds, the real estate developers agreed to
a land purchase that protected 170 acres of critical habitat
for the species.42
Perhaps most importantly, designating critical habitat
ensures that adequate focus is placed on species recovery
and not just survival.43 While other provisions of the Act
protect species from direct harm, only critical habitat man-
dates that FWS determine precisely which areas are essen-
tial to recovery. Designation of unoccupied critical habitat
is especially important for historically occupied areas and
areas that scientists believe to be essential for expanding a
species’ range in the future.44 In fact, of all the provisions
in the ESA, critical habitat designation is particularly valu-
able because it is not limited just to those areas where a
38. FWS, Designation of Critical Habitat for the New Mexico Meadow Jump-
ing Mouse, 81 Fed. Reg. 14264, 14267 (Mar. 16, 2016).
39. See U.S. Forest Service, New Mexico Meadow Jumping Mouse Habitat Im-
provement Projects on the Agua Chiquita Grazing Allotment, https://www.
fs.usda.gov/project/?project=51273 (last visited May 12, 2020). Without
critical habitat designation, it is unlikely that these areas would have re-
ceived the same priority.
40. Jack McDonald, Critical Habitat Designation Under the Endangered Species
Act: A Road to Recovery?, 28 E. L. 671, 688-91 (1998) (discussing the
notice benets of designating critical habitat).
41. See, e.g., Dashiell Farewell, Revitalizing Critical Habitat: e Ninth Circuit’s
Pro-Eciency Approach, 46 E. L. 653, 663 (2016) (“With more parties
on notice the more likely it is that habitat will receive the consideration and
protection it deserves.”).
42. See Press Release, Center for Biological Diversity, Land Purchase Protects
Essential Mississippi Habitat for Endangered Dusky Gopher Frog (May
14, 2015), https://www.biologicaldiversity.org/news/press_releases/2015/
43. Giord Pinchot Task Force v. U.S. Fish & Wildlife Serv., 378 F.3d 1059,
1070, 34 ELR 20068 (9th Cir. 2004) (requiring FWS to provide for species
recovery, not just survival, in designating critical habitat).
44. M J. B M J. R, T E N
W L 261-62 (3d ed. 1997) (“Unoccupied critical habitat is habi-
tat, the protection of which is needed to improve the species’ status quo;
that is, it is primarily needed for the recovery of the species.”). If the goal
is to recover species to a point where the Act’s protections are no longer
needed, then logically “it will be necessary to protect some of [a species’]
former habitat as well as that which it currently occupies.” Kalyani Robbins,
Recovery of an Endangered Provision: Untangling and Reviving Critical Habi-
tat Under the Endangered Species Act, 58 B. L. R. 1095, 1105 (2010).
species lives at any given moment. is is especially true
for species that have been driven to the point of extinction
by habitat loss.
It is also worth noting that critical habitat serves this vital
function in the ESA’s conservation scheme without con-
verting an area into a park or preserve or ceasing all activity
on the land. e consultation requirement that attaches to
critical habitat is directed solely at federal agency actions.45
us, so long as no federal permit is required, and no fed-
eral funding needed, designating critical habitat on private
land may have no eect on the owner’s use of the property.
Even when a federal permit is required, empirical evidence
demonstrates that §7 consultation almost never stops a pro-
posed development in its tracks. In practice, consultation
has allowed most development projects to proceed with no
more than minor modications.46
As research shows, §7 does not, in theory or practice,
hamstring all private development. Properly implemented,
it advances the ESA’s recovery goals by striking a science-
driven balance between conservation and economic activ-
ity. In fact, one could argue that FWS has generally been
too cautious in its designation of critical habitat because of
political and economically driven concerns.
III. Considering Habitat in the Wake
e Supreme Court began its analysis in Weyerhaeuser with
a bit of linguistic formalism. “According to the ordinary
understanding of how adjectives work,” the Court said,
“‘critical habitat’ must also be habitat.”47 Because “adjec-
tives modify nouns,” the Court reasoned that “[i]t follows
that ‘critical habitat’ is a subset of habitat that is ‘critical’
to the conservation of an endangered species.”48 In other
words, “[o]nly the ‘habitat’ of the endangered species is eli-
gible for designation as critical habitat.”49
At rst blush, this makes sense. e ESA states that
FWS (or NMFS for marine species) must “designate any
habitat of such species which is then considered to be criti-
cal habitat.”50 As Prof. J.B. Ruhl has noted: “Had the statute
instead used the term ‘critical areas’ or ‘critical resources,’
the question for the Court in Weyerhaeuser would have
been much dierent. But after Weyerhaeuser, you can’t take
the ‘habitat’ out of ‘critical habitat.’”51 us, according
to the Supreme Court, even if FWS nds that an area is
essential to the conservation of the species, “Section 4(a)(3)
(A)(i) does not authorize the Secretary to designate the area
as critical habitat unless it is also habitat for the species.”52
45. 16 U.S.C. §1536(a)(2).
46. Jacob Malcom & Ya-Wei Li, Data Contradict Common Perceptions About a
Controversial Provision of the U.S. Endangered Species Act, 112 P. N’
A. S. 15844, 15845 (2015) (reviewing all 88,920 FWS consultations
from January 2008 through April 2015).
47. Weyerhaeuser Co. v. U.S. Fish & Wildlife Serv., 139 S. Ct. 361, 368, 48
ELR 20196 (2018).
50. 16 U.S.C. §1533(a)(3)(A)(1) (emphasis added).
51. J.B. Ruhl, What Is Habitat?, 34 N. R E’ 52, 53 (2019).
52. Weyerhaeuser, 139 S. Ct. at 368.
7-2020 ENVIRONMENTAL LAW REPORTER 50 ELR 10535
So, what did Congress mean when it used the word
“habitat”? Legal advocates often turn to the dictionary
when a term is not clearly dened in the law. In the Wey-
erhaeuser case, the petitioners used Webster’s Dictionary to
dene habitat as “the place where a plant or animal species
naturally lives and grows,” or “the kind of site or region
with respect to physical features ... naturally or normally
preferred by a biological species.”53 By their reading of the
dictionary denition, if a species cannot currently live on
a site, then it does not “naturally” or “normally” live there,
and that area cannot qualify as habitat.
But that is not necessarily so. Such a reading fails to
examine what it means for a thing to be “natural” or even
“normal.” For example, “natural” has many denitions in
Webster’s, among them “growing without human care,”
“not cultivated,” and “closely resembling an original: true
to nature.”54 is implies a state prior to signicant human
disturbance. When understood in that frame, what “natu-
rally lives and grows” on Unit 1 are not the loblolly pines
that the landowners currently cultivate, but the longleaf
pine forests that FWS found could provide “food, shel-
ter and protection” for the frog with some restoration.55
e frog, after all, naturally—and normally—lived there
until at least 1965, when the last observations of the spe-
cies were recorded.56
Whichever view one prefers, the dictionary alone will
not settle the issue. As Professor Ruhl put it: “Apparently,
the plain meaning of ‘habitat’ is not so plain.”57
e Supreme Court correctly did not address the issue
further and remanded the case to the lower courts to con-
sider the denition of “habitat” in the rst instance. e
Court did recognize that “habitat can, of course, include
areas where the species does not currently live, given that
the statute denes critical habitat to include unoccupied
areas.”58 Alas, this further begs the question of whether an
unoccupied area must be presently habitable in order to be
considered habitat that could be designated critical. After
the Weyerhaeuser decision, FWS agreed to withdraw and
reconsider the designation of Unit 1, and the parties dis-
missed the case. Accordingly, the lower courts no longer
have the opportunity to consider the denition of habitat
in that case.
IV. Toward a Scientiﬁc Understanding
If the ESA itself is silent as to precisely what habitat means,
and dictionary denitions fail to illuminate the concept
beyond a most general (and largely unhelpful) denition,
what might science tell us? It turns out that the scientic
literature is not crystal clear either. e National Academy
of Sciences, in its seminal report Science and the Endan-
53. Brief of Petitioners at 23, Weyerhaeuser Co. v. U.S. Fish & Wildlife Serv.,
139 S. Ct. 361, 48 ELR 20196 (2018) (No. 17-71) (citing “Habitat,” W-
’ T N I D (1976)).
54. “Natural,” W’ T N I D (1976).
55. 77 Fed. Reg. at 35131.
56. Id. at 35133.
57. Ruhl, supra note 51, at 54.
58. Weyerhaeuser, 139 S. Ct. at 369.
gered Species Act, dened habitat as “the physical and bio-
logical setting in which organisms live and in which the
other components of the environment are encountered.”59
But while scientists universally agree that loss of habitat
leads to species extinction, recent reviews of the scientic
literature nd that the term is used inconsistently, even
incorrectly, in a large number of articles. In fact, the word
habitat and habitat-related terminologies are used so often
and in so many ways that David Kirk et al. have dubbed
the term to be a “Panchreston problem,” which means “an
explanation or theory used in such a variety of ways as to
One highly cited 1997 paper by Linnea Hall et al. called
for a standardized denition of habitat.61 Under their own
proered denition, habitat is “the resources and condi-
tions present in an area that produce occupancy—includ-
ing survival and reproduction—by a given organism.” at
said, dening a specic habitat is highly species-dependent.
In their view, habitat “relates the presence of a species, pop-
ulation, or individual (animal or plant) to an area’s physical
and biological characteristics. Habitat implies more than
vegetation or vegetation structure; it is the sum of the spe-
cic resources that are needed by organisms.”62
is denition emphasizes not just physical presence,
but the “resources and conditions” that support presence,
including the “sum” of the resources that an individual
species may need to survive. But from a policy perspective,
it does not settle the question posed by the Weyerhaeuser
Court. If this were the denition of habitat, would Unit 1
be considered habitat or not? It is not clear.
A broader look at the ecological literature makes clear
just how uid the concept of habitat can be. For example,
Hall et al. note specically that “‘unused’ and ‘unoccupied’
habitat are not synonymous with ‘non-habitat,’” and that
such terms are appropriate when discussing threatened,
endangered, or rare species who might use such unoc-
cupied areas given the opportunity. Others have pointed
out that habitat important for conservation can include a
wide variety of space and resource congurations, includ-
ing areas that are marginal or of low quality.63 Moreover,
the value or quality of habitat for a species can also change
over time. As the National Academy noted, “the rhythm
of natural disturbance, the waxing and waning of preda-
tor and prey population, and the cycling of soil nutrients”
among other things, can “change the distribution, growth,
abundance, and interaction of species.”64
Similarly, stopover habitats that are occupied temporar-
ily or sporadically such as during migration can be very
59. N R C, supra note 16, at 71.
60. David Anthony Kirk et al., Our Use, Misuse, and Abandonment of a Concept:
Whither Habitat?, 8 E E 4197, 4198 (2018), available
61. Linnea S. Hall et al., e Habitat Concept and a Plea for Standard Terminol-
ogy, 25 W S’ B. 173 (1997).
63. Carmen Vanbianchi et al., Navigating Fragmented Landscapes: Canada Lynx
Brave Poor Quality Habitats While Traveling, 8 E E
64. N R C, supra note 16, at 95.
50 ELR 10536 ENVIRONMENTAL LAW REPORTER 7-2020
important for species,65 as can articial or built habitats.66
Some “dispersal habitat”—habitat that “organisms occa-
sionally or periodically disperse through”—may be of little
value to a species for breeding or foraging, but may none-
theless be key to its survival in that it provides “stepping
stones or unbroken corridors” that facilitate migration. For
that matter, species may take refuge in areas that would
typically be unsuitable due to environmental stressors.67
Finally, and most critically, science tells us that “[h]abitat
restoration results in an increase in population size—and
therefore, viability—because of an expansion in available
habitat. Importantly, connecting fragments allows immi-
gration from source populations that rescue ounder-
ing populations.”68 Given that so much habitat is already
degraded, not enough “move-in-ready” habitat exists to
support both the survival and recovery of some species.
V. Toward an Operative Deﬁnition
So, where does this leave us? e Supreme Court has made
clear that “critical habitat” must be habitat, but the ESA
does not dene the term and the rst recourse of lawyers
and judges—the dictionary—does not oer a common
understanding that is nuanced enough to account for the
kinds of situations that FWS or NMFS must address in
actually designating critical habitat. Similarly, attempts
to dene habitat scientically tend to fall short as a road
map for decisionmaking, when one considers that a spe-
cies’ habitat needs can change over time and that habitat
quality can wax and wane depending on a wide range of
e structure and purpose of the ESA is perhaps the
best guide. e goal of the ESA is to conserve imperiled
species. e ESA denes “conservation” as “the use of all
methods and procedures which are necessary to bring any
endangered species or threatened species to the point at
which the measures provided pursuant to this Act are no
longer necessary.” As the Supreme Court noted in Tennes-
see Valley Authority v. Hill, the “plain intent of Congress
in enacting [the ESA] was to halt and reverse the trend
towards species extinction, whatever the cost.”69 us, any
denition of habitat adopted by FWS and NMFS should
further that conservation goal.
Congress also required FWS and NMFS to utilize the
“best scientic data available” in designating critical habi-
tat. Principles of ecology, including the dynamic nature of
habitat, the life-cycle needs of species, and other factors,
thus must inform the decision.
65. Justin Sheehy et al., e Importance of Stopover Habitat for Developing Eec-
tive Conservation Strategies for Migratory Animals, 152 J. O 161,
66. Hugh L. Wright et al., Agriculture—A Key Element for Conservation in the
Developing World, 5 C L 11 (2012).
67. N R C, supra note 16, at 101.
68. William D. Newmark et al., Targeted Habitat Restoration Can Reduce Extinc-
tion Rates in Fragmented Forests, 114 P. N’ A. S. 9635, 9635
69. 437 U.S. 153, 184-85, 8 ELR 20513 (1978).
With all this in mind, a denition that reects the best
available science, is consistent with the intent of the ESA,
and is broad enough to account for species’ needs might
look like the following:
Habitat is the area or type of site where a species naturally
occurs or that it depends on directly or indirectly to carry
out its life processes, or where a species formerly occurred
or has the potential to occur and carry out its life processes
in the foreseeable future.
e proposed denition has a number of features. It is
consistent with habitat denitions from the scientic lit-
erature, and it accommodates existing regulatory de-
nitions and key concepts essential to implementing the
ESA. It is separate from but complementary to the ESA’s
denition of “critical habitat.” And, as discussed further
below, it is operational.
First, the proposed denition respects the ESA’s deni-
tion of “critical habitat,” which divides the designations
into currently occupied or unoccupied habitat. Second,
it is centered on identifying areas of interest that can
be mapped, not just a list of the “physical and biologi-
cal features” present in any given area. Taking more of
a landscape view of habitat rather than looking only at
associations of factors a species needs, such as temperature
regimes or specic vegetation, allows for a more holistic
assessment. ird, it recognizes that because of material
and energy ows in real ecosystems, areas that indirectly
contribute to a species’ life processes are part of habitat
Finally, it includes a temporal component. Deni-
tions of habitat in the scientic literature generally do
not include a temporal restriction, but critical habitat in
the ESA must be considered at least to the horizon of the
foreseeable future because these areas are “essential to the
conservation of the species”—that is, to recovery. e pro-
posed denition recognizes that there is a temporal com-
ponent to critical habitat and allows for the possibility that
species have “the potential to occur” and even thrive in
is denition of “habitat” is broad enough to encom-
pass areas where a species currently lives, areas that spe-
cies depend upon for portions of their life cycle, areas that
could presently support reintroduction, areas that could
reasonably be restored or could be expected to support
range expansion in the future, and places that provide
essential nutrients or services to such areas. is gives FWS
the exibility needed to determine specically what por-
tions of a species’ range (current, historic, or potential) are
in fact “critical” and require designation as areas “essential
to the conservation of the species.”
VI. Applying the Deﬁnition
How would this denition work in practice? As a thresh-
old matter, it is important to note that the need to parse
what “habitat” is only arises when FWS or NMFS consider
designating unoccupied habitat. If the area is already occu-
7-2020 ENVIRONMENTAL LAW REPORTER 50 ELR 10537
pied, then there should be no question under any deni-
tion that the area is habitat for the species. Moreover, under
current regulations, FWS and NMFS are only permitted
to designate unoccupied habitat after concluding that the
remaining occupied habitat is not sucient to conserve
the species.70 is rule was briey abandoned during the
Barack Obama Administration and was recently revived.
So, for many critical habitat designations, unoccupied hab-
itat may not even come into play.
In a recent essay, Professor Ruhl posits four scenarios
where a clear denition of habitat could impact designa-
tions of unoccupied habitat. e rst scenario involves
areas that are essentially intact or “move-in ready.” All
that is required is for the species to make its way there
or be reintroduced. Everything the species needs is pres-
ent and it is understood that the species can live there.
ese areas seem, in his words, “squarely to be a candi-
date for critical habitat—it’s habitat just waiting to be
occupied.”71 Under virtually any denition of habitat,
these areas could be designated.
e second scenario is “an area that is unoccupied and
could never practicably be made occupiable for the spe-
cies, naturally or through human intervention.”72 is is
essentially the hypothetical that Chief Justice John Rob-
erts posited during the oral argument in Weyerhaeuser,
when he asked counsel for the government whether
you could simply move the frogs to ephemeral ponds in
Alaska, build a greenhouse around them, and call it criti-
cal habitat.73 In this scenario, the area in question cannot
sustain the species and cannot be meaningfully restored
or converted to habitat. is is an easy case: an ephem-
eral pond greenhouse in Alaska would never be habitat; it
would be a zoo. Similarly, no one would seriously consider
the former polar bear enclave at the Smithsonian National
Zoo to be habitat even though bears lived there (happily
or not) for decades.
In between these scenarios, we have the actual facts
of Weyerhaeuser—an area within the historic range
of the species that is presently unoccupied and argu-
ably unoccupiable. In this example, the area has been
degraded due to human intervention or natural causes,
but with some degree of eort it could be restored and
once again support the species. Inherent in this example
is whether critical habitat must be immediately habitable
in order to qualify as habitat. e proposed denition
would allow Unit 1 to be designated critical habitat if the
record evidence supported a nding that it is essential
to the conservation of the species, regardless of whether
the property was immediately habitable. While it is fair
to argue the Weyerhaeuser Court was skeptical of such a
view, the Court did not decide what habitat is, nor did it,
in remanding the case to consider what habitat means in
70. 50 C.F.R. §424.12(b)(2) (2019); FWS, NMFS, Regulations for Listing Spe-
cies and Designating Critical Habitat, 84 Fed. Reg. 45020 (Aug. 27, 2019).
71. Ruhl, supra note 51, at 53.
73. Oral Argument Transcript at 29, Weyerhaeuser Co. v. U.S. Fish & Wildlife
Serv., 139 S. Ct. 361, 48 ELR 20196 (2018) (No. 17-71), https://www.su-
the rst instance, expressly require habitat to be immedi-
e question then is what level of restoration is too
much? Although Chief Justice Roberts’ Alaska hypotheti-
cal goes too far, it does raise a legitimate question of limits.
As he put it at the time, “there has to be presumably some
limit on what restoration you would say is required.”75
Later in the argument, Justice Samuel Alito raised a similar
question: “I think your argument requires you to provide
some denition of reasonable restoration.”76
But that is a dierent question than whether the best
available scientic data indicate that the area should be
considered habitat essential to species recovery. Ratio-
nal basis review requires an application of specic facts.
Once FWS and NMFS have dened habitat in a way that
could be deemed an exercise of agency discretion worthy of
judicial deference, the task of deciding what is reasonable
is much simpler. It is no dierent, really, than the other
question at issue in Weyerhaeuser—whether FWS’ decision
not to exclude an area from critical habitat as imprudent is
subject to judicial review. In most cases, a reasoned agency
decision will be upheld.77 When the facts do not support
the decision, it will not.78
Professor Ruhl’s fourth scenario involves areas outside
the historic range of the species that may become habit-
able due to climate change or human intervention to
change the ecological conditions of the site beyond res-
toration. Professor Ruhl himself argued in a 2018 article
that such areas could be designated as critical habitat,79 but
he now believes the argument is “tenuous at best” because
it did not rely on the premise that “critical habitat” must
be “habitat.”80 While this may indeed be the least solid
ground on which to hang a critical habitat designation, the
proposed denition would allow it with the proviso that
the habitat transition must be foreseeable. FWS already
makes listing determinations on the basis of threats that
are non-imminent but reasonably foreseeable. A similar
approach could be taken where there is evidence that spe-
cies are beginning to shift their range in response to cli-
mate change. If a duly enacted regulation were to dene
habitat to include areas that will be essential to the conser-
74. Weyerhaeuser, 139 S. Ct. at 369:
e Court of Appeals concluded that “critical habitat” designations
under the statute were not limited to areas that qualied as habitat.
See [Markle Interests, L.L.C. v. U.S. Fish & Wildlife Serv., 827
F.3d 452, 468 (5th Cir. 2016)] (“ere is no habitability require-
ment in the text of the ESA or the implementing regulations.”). e
court therefore had no occasion to interpret the term “habitat” in
Section 4(a)(3)(A)(i) or to assess the Service’s administrative nd-
ings regarding Unit 1. Accordingly, we vacate the judgment below
and remand to the Court of Appeals to consider these questions in
the rst instance.
75. Oral Argument Transcript at 29, Weyerhaeuser (No. 17-71).
76. Id. at 35.
77. Baltimore Gas & Elec. Co. v. Natural Res. Def. Council, Inc., 462 U.S. 87,
103, 13 ELR 20544 (1983) (“When examining this kind of scientic deter-
mination ... a reviewing court must generally be at its most deferential.”).
78. Motor Vehicle Mfrs. Ass’n of the United States, Inc. v. State Farm Mut.
Auto. Ins. Co., 463 U.S. 29, 42-43, 13 ELR 20672 (1983) (applying the
arbitrary and capricious standard to agency actions).
79. J.B. Ruhl, Climate Change and the Endangered Species Act: Building Bridges
to a No-Analog Future, 88 B.U. L. R. 1 (2008).
80. Ruhl, supra note 51, at 53.
50 ELR 10538 ENVIRONMENTAL LAW REPORTER 7-2020
vation of the species in the foreseeable future, any determi-
nation FWS made to that eect would again be reviewable
under a rational basis test.
ere is, however, one additional scenario that the pro-
posed denition contemplates, and that is unoccupied,
uninhabitable areas that nonetheless are critically impor-
tant to sustaining the species and its occupied habitat.
Unlike some of the hypotheticals considered above, this
one is real. A good example is the upstream reaches of
the Big Tujunga Creek that provide stream and sediment
ows necessary for the survival of the Santa Ana sucker in
downstream occupied areas,81 or the sandy desert north of
Ramon Road in Riverside County, California, that pro-
vides the source of windblown sand essential to the con-
servation of the Coachella Valley fringe-toed lizard in its
range to the south.82
e proposed denition expressly countenances the
possibility of designating areas like these that are not them-
selves habitable, but that provide the physical or biological
features that are essential to the survival of the species in
occupied areas. Indeed, the U.S. Court of Appeals for the
Ninth Circuit expressly rejected the argument that unoccu-
pied but essential upstream areas should be excluded from
the Santa Ana sucker designation because these areas were
not occupied (or occupiable) habitat. As the court held,
“[t]here is no support for this contention in the text of the
ESA or the implementing regulation, which requires the
Service to show that the area is ‘essential,’ without further
dening that term as habitable.”83 While the Weyerhaeuser
decision may call this holding into question, under the pro-
posed denition of habitat, it would stand.
Consistent with the purpose of the ESA to conserve
species, the essentiality of the area to species recovery, not
its present habitability, should be at the core of any under-
standing of habitat. is not only makes biological and
policy sense, it addresses a practical limitation of the ESA.
Without designation as critical habitat, these unoccupied
areas would not generally receive any protection. at is
because while an action “does not have to occur on desig-
nated critical habitat to trigger Section 7 consultation,”84
where no critical habitat is designated, only the possibil-
ity of impact to species present in the area will prompt
consultation.85 Actions solely aecting unoccupied areas
will thus never trigger §7’s “may aect” standard for a
Critics of the proposed denition might argue that this
approach attempts too much. As Professor Ruhl suggests,
81. 75 Fed. Reg. 77961, 77973 (Dec. 14, 2010).
82. 45 Fed. Reg. 63812, 63818 (Sept. 25, 1980).
83. Bear Valley Mut. Water Co. v. Jewell, 790 F.3d 977, 994, 45 ELR 20121
(9th Cir. 2015). Similarly, when it considered the designation of unoccu-
pied areas for the dusky gopher frog, the U.S. Court of Appels for the Fifth
Circuit found that “there is no habitability requirement in the text of the
ESA or the implementing regulations.” Markle Interests, L.L.C. v. U.S. Fish
& Wildlife Serv., 827 F.3d 452, 468 (5th Cir. 2016).
84. Markle Interests, L.L.C. v. U.S. Fish & Wildlife Serv., 848 F.3d 635, 645
(5th Cir. 2017) (Jones, J., dissenting).
85. FWS NMFS, E S C H 3-11,
pdf (“A biological assessment is required if listed species or critical habitat
may be present in the action area.”).
“Perhaps a way to reconcile all this is to acknowledge that
the ESA was not designed to be the exclusive mechanism
for conserving species in peril. If critical habitat must be a
subset of habitat, habitat should be dened in a way that
does not stretch credulity.”86 But while Professor Ruhl
thinks it may be a “big jump” to include restorable areas
of a species’ historic range, areas in transition due to cli-
mate change, or areas that contribute essential resources
to undisputed habitat, this may well be what conservation
under the ESA requires.
As for the need for limiting principles, it is unlikely
that FWS or NMFS will suddenly begin designating large
swaths of uninhabitable areas under the proposed deni-
tion. First, as noted above, the Services can only designate
unoccupied areas after concluding that there is not enough
occupiable habitat to conserve the species. Second, in some
cases, the unoccupied habitat will be part of the species’
historic range and will require little to no restoration. e
proposed denition would not change the status quo in
ird, as an empirical matter, the Services rarely des-
ignate unoccupied critical habitat. One survey of critical
habitat designations between 2003 and 2012 found that
“unoccupied habitat was included as part of critical habi-
tat for less than one third of the species we considered.”87
Fourth, FWS and NMFS have already addressed the Wey-
erhaeuser case in new regulations “by adding a require-
ment that, at a minimum, an unoccupied area must
have one or more of the physical or biological features
essential to the conservation of the species in order to be
considered as potential critical habitat.”88 is regulation
also ensures that future designations of unoccupied habi-
tat will not be untethered from reality. Ultimately, very
few additional designations will likely be made possible
by the proposed denition, but those that are could be
the dierence between recovery and extinction for the
Finally, even under a broad denition of habitat, the
judiciary will act as a check on overly expansive designa-
tions. Under the ESA, in order to designate such areas,
FWS or NMFS must still nd that a presently unoccupied
area is “essential for the conservation of a species.”89 e
designation must be supported by the best available scien-
tic data and can only be made after taking into account
economic and other factors. While those technical deter-
minations are entitled to deference, they are reviewable for
abuse of discretion. In situations where the scientic merit
is lacking or the costs of designations clearly outweigh the
benets, the Services cannot lawfully include the area in
86. Ruhl, supra note 51, at 54.
87. Abbey E. Camaclang et al., Current Practices in the Identication of Criti-
cal Habitat for reatened Species, 29 C B 482, 482-92
(2014); see also Stephanie Brauer, Arizona Cattle Growers’ Pyrrhic Victory for
Critical Habitat, 38 E L.Q. 369, 379 (2011) (“Despite its impor-
tance, unoccupied habitat constitutes ‘a relatively small amount of habitat
designated as critical habitat.’”).
88. 84 Fed. Reg. at 45022 (“We note that we do not in the rule attempt to
denitively resolve the full meaning of the term ‘habitat.’”).
89. 16 U.S.C. §1533(b)(2).
7-2020 ENVIRONMENTAL LAW REPORTER 50 ELR 10539
e dusky gopher frog case illustrates just how dicult
it can be for FWS to designate unoccupied critical habi-
tat. Indeed, the Service designated Unit 1 as unoccupied
critical habitat only after making a scientic determina-
tion that existing occupied critical habitat was insucient
to conserve the frog. e Service’s original proposal only
included occupied sites within Mississippi.90 But scientic
peer reviewers of the proposed rule “were united in their
assessment that this proposal was inadequate for the con-
servation of the dusky gopher frog.”91
Before designating Unit 1, FWS surveyed recorded
sightings of the frog throughout its historic range and fol-
lowed up on those leads with detailed aerial and on-the-
ground surveys of potential remnant habitat.92 It also ruled
out many other areas in both Alabama and Louisiana that
lacked the breeding ponds that are so important to the frog’s
life cycle.93 Finally, the Service weighed the economic bur-
den of designating Unit 1 against the conservation benet
from such action and determined that it was not appropri-
ate to exclude these tracts.94 As the U.S. Court of Appeals
for the Fifth Circuit explained: “e Final Designation was
based on the scientic expertise of the agency’s biologists
and outside gopher frog specialists. If this scientic support
were not in the record, the designation could not stand.”95
90. 75 Fed. Reg. 31387, 31395 (proposed June 3, 2010).
91. 77 Fed. Reg. at 35123-24.
92. Id. at 35133 (noting that the five ponds on Unit 1 were of “remark-
94. Id. at 35140-41.
95. Markle Interests, L.L.C. v. U.S. Fish & Wildlife Serv., 827 F.3d 452, 472
(5th Cir. 2016).
Nearly 50 years since the passage of the ESA, biodiver-
sity remains in crisis. Species are now going extinct at an
unprecedented rate. Although the ESA is rightly credited
with helping to recover or stabilize many species on the
endangered and threatened species list,96 hundreds more
await listing decisions. Moreover, climate change threat-
ens to undermine much of the progress we have made in
protecting species and habitats in the United States and
around the world. Whatever we are doing to preserve the
world as we know it is not enough.
e ESA’s purpose is to recover species to the point
that the Act’s protections are no longer necessary.97 at
lofty goal will only be possible if every aspect of the stat-
ute is used to its maximum potential. Critical habitat is
a historically underutilized conservation tool that could
yield signicant benets for species. is is not the time
to unnecessarily restrict the tools we have to conserve wild
places and wildlife.
At the end of the day, the Supreme Court’s admoni-
tion that “critical habitat” must rst be “habitat” does not
actually tell us very much. Accordingly, FWS, NMFS, and
Congress should consider the conservation purposes of the
ESA and adopt a denition of habitat, like the one we pro-
pose, that will provide the exibility to recover species in
these challenging times. As this Comment has hopefully
shown, FWS and NMFS can designate unoccupied critical
habitat consistent with legal and ecological principles and
still meet the evolving needs of America’s wildlife.
96. See Noah Greenwald et al., Extinction and the U.S. Endangered Species Act, 7
PJ e6803 (2019), available at https://peerj.com/articles/6803.pdf; Dan-
iel M. Evans et al., Species Recovery in the United States: Increasing the Eec-
tiveness of the Endangered Species Act, I E, Winter 2016, https://
97. 16 U.S.C. §1532(3).