New Mexico Cattle Growers ’ Association v. United States Fish and Wildlife Service

United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued February 3, 2025 Decided August 22, 2025
No. 24-5075
NEW M EXICO C ATTLE G ROWERS ’ ASSOCIATION ,
APPELLANT
v.
UNITED S TATES F ISH AND WILDLIFE S ERVICE, ET AL.,
APPELLEES
Appeal from the United States District Court
for the District of Columbia
(No. 1:21-cv-03263)
Charles T. Yates argued the cause for appellant. With him
on the briefs were Paige E. Gilliard and Damien M. Schiff.
Amelia G. Yowell, Attorney, U.S. Department of Justice,
argued the cause for federal appellees. With her on the brief
were Todd Kim, Assistant Attorney General, and Joan M.
Pepin, Attorney.
Ryan A. Shannon argued the cause for appellees Center for
Biological Diversity and Maricopa Audubon Society. With
him on the brief was Margaret E. Townsend.
Before: P ILLARD , R AO and C HILDS , Circuit Judges.

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Opinion for the Court filed by Circuit Judge P ILLARD.
P ILLARD, Circuit Judge: Since 1995, the Fish and
Wildlife Service has recognized the southwestern willow
flycatcher—a small, migratory songbird—as an endangered
subspecies of the willow flycatcher. The New Mexico Cattle
Growers’ Association petitioned the Service to remove that
designation, arguing that the southwestern willow flycatcher is
not a valid subspecies and thus does not qualify for listing as
an endangered species. When the Service rejected that
argument and reaffirmed the bird’s subspecies classification,
Cattle Growers sued, and the district court ruled against it on
summary judgment.
On appeal, Cattle Growers argues that the Service’s
determination was arbitrary and capricious because it failed to
articulate any discernible standard for evaluating subspecies
validity. In particular, Cattle Growers insists that the Service
used a “non-falsifiable,” impermissibly manipulable method of
evaluating scientific research that rendered its decision
inherently arbitrary and capricious.
Cattle Growers’ arguments have no merit. It decries the
Service’s standard as “non-falsifiable” merely because the
Service relied on studies the results of which were affected by
the researchers’ data selection and study design. But that is in
the nature of empirical research, and there is no requirement
that agencies somehow evaluate data using standards that do
not reflect accepted scientific research methodology. Well-
established principles of arbitrary and capricious review
require only that the Service’s determination be reasonable and
reasonably explained—a bar that the Service’s thorough
determination easily clears.

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I.
A.
The Endangered Species Act “provide[s] a program for the
conservation of . . . endangered species and threatened
species.” 16 U.S.C. § 1531(b). To that end, the Act directs the
Secretary of the Interior—who has delegated his responsibility
(as relevant here) to the Fish and Wildlife Service, 50 C.F.R.
§ 402.01(b)—to maintain a list of threatened and endangered
species. See 16 U.S.C. §§ 1533(a)(1), (c)(1). Listed species
are afforded a host of protections under the Act. For instance,
it is generally illegal to harass, harm, capture, or kill an animal
that belongs to a species listed as “endangered.” Id.
§§ 1538(a)(1)(B), 1532(19).
Only animal populations that qualify as a “species”—
defined by the Act to include subspecies, id. § 1532(16)—can
be listed as threatened or endangered. See id. § 1533(c)(1); 50
C.F.R. § 424.11(a). The Service’s regulations specify that,
“[i]n determining whether a particular taxon or population is a
species for the purposes of the Act, the [Service] shall rely on
standard taxonomic distinctions and the biological expertise of
the Department [of the Interior] and the scientific community
concerning the relevant taxonomic group.” 50 C.F.R.
§ 424.11(a). The Act requires the Service to make that
determination “solely on the basis of the best scientific and
commercial data available.” 16 U.S.C. § 1533(b)(1)(A).
Any “interested person” may petition the Service under the
Endangered Species Act to add, remove, or reclassify a species
(including a subspecies) from the list of threatened and
endangered species. Id. § 1533(b)(3)(A). Within 90 days of
receiving such a petition, the Service must determine “whether
the petition presents . . . substantial information” that the
requested status change “may be warranted.” Id. If the Service

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decides the petition meets that threshold, it must issue a finding
within 12 months as to whether the requested status change is
in fact warranted. Id. § 1533(b)(3)(B).
B.
The southwestern willow flycatcher was first described as
a subspecies of the willow flycatcher in 1948. Final Rule
Determining Endangered Status for the Southwestern Willow
Flycatcher, 60 Fed. Reg. 10,694, 10,696 (Feb. 27, 1995).
Further taxonomic studies conducted by ornithologists in the
1980s and 1990s supported that subspecies classification.
They found, for example, that the southwestern willow
flycatcher had a paler color, different wing length, and “more
protracted, slurred ‘fit-za-bew’” song compared to the “sneezy
‘fitz-bew’” song of the four northern subspecies of willow
flycatcher. Id. at 10,694-96. In 1995, consistent with the
“majority opinion” among ornithologists at the time, the
Service determined that the southwestern willow flycatcher
was a valid subspecies, even as it “acknowledge[d] that
taxonomy of [the southwestern willow flycatcher] continues to
pose questions and may be revised in the future.” Id. at 10,698.
The Service also concluded that the southwestern willow
flycatcher was endangered and listed it as an endangered
species. Id. at 10,713.
Scientists continued to study the southwestern willow
flycatcher’s taxonomy following its 1995 listing as an
endangered species. To that end, researchers collected and
evaluated southwestern willow flycatcher DNA, plumage
coloration measurements, and song samples using more
advanced, quantitative techniques than those used in the pre-
listing studies. The post-listing studies concluded that
subspecies classification was warranted, supporting the
Service’s 1995 subspecies designation. In 2015, however,

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biologist Robert Zink reanalyzed the data that other researchers
had used to confirm the southwestern willow flycatcher’s
subspecies designation, critiqued those previous studies’
research methods and conclusions, and concluded that the
Service’s subspecies designation was wrong. See Robert M.
Zink, Genetics, morphology, and ecological niche modeling do
not support the subspecies status of the endangered
Southwestern Willow Flycatcher (Empidonax traillii extimus),
117 THE C ONDOR : ORNITHOLOGICAL APPLICATIONS 76 (2015)
(J.A. 478); see also Notice of 12-Month Petition Finding and
5-Year Review (Notice) 6 (J.A. 580). Zink did not collect any
new data to support his analysis.
Shortly after Zink’s article was published, a number of
organizations, including the New Mexico Cattle Growers’
Association (Cattle Growers), jointly petitioned the Service to
remove the southwestern willow flycatcher from the
endangered species list. Petition to Remove the
“Southwestern” Willow Flycatcher (Empidonax traillii
“extimus”) (SWWF) From the List of Endangered Species
Under the Endangered Species Act Due to Significant New
Data that Demonstrates Original Data Error (Petition) 1 (J.A.
490). The petition argued that neither pre-listing nor post-
listing data supported subspecies classification, as
demonstrated by Zink’s reanalyses of those data. See id. at 12
(J.A. 501). The petition relied heavily on Zink’s article,
adopting its conclusions as well as its critiques of the sampling
choices and hypothesis design of post-listing studies that
validated the subspecies designation.
The Service determined that the petition presented
substantial information suggesting that the southwestern
willow flycatcher’s subspecies designation may have been
incorrect and accordingly initiated a 12-month review.
Evaluation of a Petition to Remove the Southwestern Willow

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Flycatcher From the List of Endangered and Threatened
Wildlife, 81 Fed. Reg. 14,070 (Mar. 16, 2016) (J.A. 567). After
inviting public comment, reviewing the body of existing
scientific literature evaluating the validity of the subspecies
classification—including a published, peer-reviewed paper
authored by Tad Theimer rebutting Zink’s analyses—and
consulting with experts, the Service concluded that delisting
was not warranted, as the best available evidence continued to
support subspecies classification. 12-Month Findings on
Petitions to List a Species and Remove a Species from the
Federal Lists of Endangered and Threatened Wildlife and
Plants, 82 Fed. Reg. 61725, 61726-27 (Dec. 29, 2017) (J.A.
668-69); Notice 7-8 (J.A. 581-82).
The Service laid out its reasoning in a detailed, 91-page
report. First, the Service explained the framework and criteria
it used to determine whether the “best available scientific and
commercial information” supported subspecies classification,
as required under the Endangered Species Act. Notice 8 (J.A.
582); see also 16 U.S.C. § 1533(b)(1)(A). In accord with its
regulatory obligation to “rely on standard taxonomic
distinctions and the biological expertise of the Department [of
the Interior] and the scientific community” in “determining
whether a particular taxon or population is a species[, including
a subspecies,] for the purposes of the Act,” 50 C.F.R.
§ 424.11(a), the Service adopted a “common” definition of
subspecies to refer to two sets of organisms of the same species
that are “capable of interbreeding and producing fertile
offspring, but usually do not interbreed in nature due to
geographic isolation, sexual selection, or other factors.” Notice
9 (J.A. 583). The Service then explained that in avian
taxonomy, scientists often determine whether that definition of
subspecies is met by identifying instances of “non-clinal
geographic variation.” Id.

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Because the concept of “non-clinal geographic variation”
is key to understanding the Service’s analysis as well as Cattle
Growers’ arguments, it is worth explaining in some detail.
When scientists plot a given trait (e.g., size) as observed across
a species’ geographic range, the data typically produce a
gradual slope, called a smooth cline, indicating incremental
adaptation to environmental changes across the species’ range.
See Tad C. Theimer et al., Available data support protection of
the Southwestern Willow Flycatcher under the Endangered
Species Act, 118 THE C ONDOR : ORNITHOLOGICAL
APPLICATIONS 289, 290 (2016) (Theimer 2016) (J.A. 535). For
example, within the same species of bird, specimens might
typically be larger in cooler climates and smaller in warmer
climates, with gradual differences in specimen size
corresponding to climate variation across the species’ range.
Specimen size plotted on a graph from north to south would
show a smooth downslope.
“Non-clinal” change, by contrast, appears irregular or
interrupted rather than smooth, reflecting relatively rapid
variation in specimens’ traits within a small geographic area.
“Non-clinal geographic variation” thus refers to abrupt changes
in species traits over short geographic distances, which—
critically—indicates the existence of a subspecies. See Notice
9, 17 (J.A. 583, 591).
Turning back to the Service’s analysis of Cattle Growers’
petition, the Service first reviewed the body of relevant
scientific studies, explaining how the data collected and
analyzed post-listing—but before Zink’s critique—had
revealed statistically significant differences in willow
flycatcher song, plumage, and genetics, supporting subspecies
classification. Against that backdrop, the Service found that
Zink’s reanalyses of that data contained significant “errors,
incorrect analyses, and limitations,” and that it thus did “not

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represent the best available scientific information sufficient to
restructure the taxonomy of [the willow flycatcher] and negate
recognition of the southwestern subspecies.” Id. at 23-24 (J.A.
597-98).
For instance, a genetic study from 2007 had analyzed
southwestern willow flycatcher DNA samples and found a
“sharp change of genetic frequencies at the subspecies
[geographic] boundary” supporting subspecies classification.
Id. at 17 (J.A. 591). Zink maintained that the 2007 study had
graphed the data incorrectly and concluded that, when the data
were graphed correctly, they showed only a “gradual
transition” inconsistent with subspecies classification. Id. But
the Service found that “it was actually Zink [] who had graphed
the data incorrectly,” and Theimer’s correct reanalysis of the
raw data “indicate[d] a transition in haplotype frequencies
consistent with a step cline rather than the smooth cline
suggested by Zink.” Id. at 17 (J.A. 591); see also id. at 23 (J.A.
597). The Service thus concluded that “the best available
information currently still demonstrates that the genetic
information supports separation of [the southwestern willow
flycatcher] from other willow flycatcher subspecies.” Id. at 18
(J.A. 592).
Similarly, a study of southwestern willow flycatcher
plumage coloration conducted in 2010 found “strong statistical
differences among the willow flycatcher subspecies” within a
defined geographic range. Id. at 20 (J.A. 594). Zink faulted
the study for not including bird specimens from the subspecies
boundary regions and conducted a reanalysis that included
those specimens, finding a “linear relationship consistent with
a smooth cline in plumage variation” and inconsistent with
subspecies classification. Id. But Theimer’s subsequent
reanalysis, which also included the boundary specimens but
employed more advanced statistical techniques, “found

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evidence for a step-cline along the subspecies boundary.” Id.
The Service noted that, while both reanalyses “provided
reasonable opinions and analysis,” Theimer’s analysis “us[ed]
methods specific to the evaluation of morphology, clines, and
hybrid zones,” thereby adding “further rigor” to the original
plumage information and “contribut[ing] to the best available
information” demonstrating non-clinal geographic variation in
plumage coloration. Id. at 20-21 (J.A. 594-95).
The Service also found that Zink’s reanalysis of birdsong
data was of “uncertain[]” value in contributing toward the “best
scientific information” because the original song data were not
fully available. Id. at 19 (J.A. 593). Because of that limitation,
the Service determined that the original study, which found
statistically significant differences between the songs of
southwestern willow flycatchers and another subspecies of
willow flycatcher, remained the “best available commercial
and scientific information.” Id. at 19-20 (J.A. 593-94).
In sum, after analyzing in detail and ultimately rejecting
the petition’s critiques of individual studies, the Service
determined that the best available information showed non-
clinal geographic variation in southwestern willow flycatcher
genetics and plumage coloration and statistically significant
differences in southwestern willow flycatcher birdsong as
compared to the willow flycatcher species, all of which
supported subspecies classification. The Service also
explained that its conclusion that the southwestern willow
flycatcher remained a valid subspecies was informed by the
“large body of literature developed by the scientific community
that has shaped willow flycatcher and subspecies
classification.” Id. at 24 (J.A. 598). The Service noted that the
studies comprising that body of literature

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have originated, been reviewed, and withstood debate
among independent, university, and state and federal
scientists, and their results have been reviewed,
reported, and also published in ornithological
scientific journals. These materials have
subsequently been evaluated by the various sources
that track, evaluate, and make taxonomic decisions
that currently support the recognition of [willow
flycatcher] subspecies.
Id. In contrast to that well-supported consensus, the Service
explained that “the petition’s critiques of other scientist’s work
[were] comprised of questionable analyses” and reached
“inaccurate conclusion[s].” Id. As such, the Service found that
neither Zink’s article nor the petition’s commentary
“represent[ed] the best available scientific information
sufficient to . . . negate recognition of the southwestern
subspecies” of willow flycatcher. Id.
Cattle Growers sued in district court, arguing that the
Service’s determination was arbitrary and capricious in
violation of the APA because the Service failed to define
“subspecies,” provided “no governing criteria for determining
whether any given population . . . qualifies as a subspecies,”
and ignored relevant evidence. See N.M. Cattle Growers’
Ass’n v. U.S. Fish & Wildlife Serv., No. 21-cv-3263, 2024 WL
894911, at *7 (D.D.C. Feb. 28, 2024). The Center for
Biological Diversity and the Maricopa Audubon Society
intervened on behalf of the Service. Id. The district court
entered summary judgment in favor of the Service and the
intervenors, and Cattle Growers timely appealed.
II.
Cattle Growers’ disagreement with the Service’s
determination is narrow: It argues only that the Service failed

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to use a “non-arbitrary” standard for evaluating the
appropriateness of subspecies classification for the
southwestern willow flycatcher. According to Cattle Growers,
the non-clinal geographic variation standard used by the
Service is impermissibly indeterminate; a “majority opinion”
standard is arbitrary; and a “best available evidence” standard
is not a standard at all, but rather an evidentiary requirement.
Cattle Growers Br. 28-30. None of those challenges succeeds.
Cattle Growers’ critique of the non-clinal geographic variation
standard boils down to disagreement with the Service’s
reasonable assessment of competing scientific studies, which
comfortably survives arbitrary and capricious review. And,
contrary to Cattle Growers’ contentions, the Service did not use
a “majority opinion” or “best available evidence” standard to
guide its subspecies determination. The Service’s
determination is neither arbitrary nor capricious.
We review de novo the district court’s grant of summary
judgment. See Safari Club Int’l v. Zinke, 878 F.3d 316, 325
(D.C. Cir. 2017). Much judicial review under the APA is
deferential, asking only whether the agency’s action was
“arbitrary, capricious, [or] an abuse of discretion.” Loper
Bright Enters. v. Raimondo, 603 U.S. 369, 392 (2024)
(alteration in original) (quoting 5 U.S.C. § 706(2)(a)). Agency
action is arbitrary and capricious “if the agency has relied on
factors which Congress has not intended it to consider, entirely
failed to consider an important aspect of the problem, offered
an explanation for its decision that runs counter to the evidence
before the agency, or is so implausible that it could not be
ascribed to a difference in view or the product of agency
expertise.” Motor Vehicle Mfrs. Ass’n of the U.S., Inc. v. State
Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983). We must
ensure that the agency “examine[d] the relevant data and
articulate[d] a satisfactory explanation for its action including
a rational connection between the facts found and the choice

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made.” Id. (internal quotation marks omitted). But the scope
of our review under the arbitrary and capricious standard is
“narrow,” and we cannot “substitute [our] judgment for that of
the agency.” Id. We therefore must “avoid[] . . . direct[ing]
the agency in a choice between rational alternatives.” Shafer
& Freeman Lakes Env’t Conservation Corp. v. FERC, 992
F.3d 1071, 1090 (D.C. Cir. 2021) (internal quotation marks
omitted).
Cattle Growers principally argues that the non-clinal
geographic variation standard used by the Service is arbitrary
and capricious because it is “inherently non-falsifiable”—that
is, it can be manipulated “to inevitably produce an affirmative
subspecies conclusion (or not), based purely on the information
[the study author] decides to assess.” Reply Br. 12-13. In
essence, Cattle Growers contends that the non-clinal
geographic variation model is indeterminate because its results
depend on which datapoints are included in a study, allowing
the Service to manufacture an “affirmative subspecies
conclusion” by relying on studies that exclude data that would
undermine a subspecies determination. See Cattle Growers Br.
41-45. Cattle Growers asserts that any such “non-falsifiable”
standard necessarily fails arbitrary and capricious review
because the regulated public has no way to “perceive the
principles which are guiding agency action,” Pearson v.
Shalala, 164 F.3d 650, 661 (D.C. Cir. 1999), and courts have
no way to “assess the validity” of the agency’s decision
making. Cattle Growers Br. 46-47.
To begin with, that argument is forfeited, as no critique of
the non-clinal geographic variation standard was raised before
the agency. See Advocs. for Highway & Auto Safety v. Fed.
Motor Carrier Safety Admin., 429 F.3d 1136, 1150 (D.C. Cir.
2005). To the contrary, Cattle Growers’ petition to the agency
relied on that very standard to argue that the absence of non-

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clinal geographic variation in willow flycatcher traits
invalidated the Service’s subspecies classification. See, e.g.,
Petition 4 (J.A. 493) (“[G]enetic data . . . support the existence
of a genetic cline, rather than clearly defined . . . subspecies”);
id. at 5 (J.A. 494) (“The reanalysis reveals a gradual genetic
transition from one geographic location to another and does not
support the subspecies limits of the [southwestern willow
flycatcher]”); id. at 17 (J.A. 506) (arguing that putative
boundaries “are merely gradations in changes in color patterns
rather than diagnostic breaks that would allow non-arbitrary
subspecies limits”); id. at 18 (J.A. 507) (“Zink (2015) showed
that the pattern of genetic variation is gradual, rather than there
being two distinctive subspecies.”).
Even if it were properly before us, Cattle Growers’
argument would fail. The Administrative Procedure Act does
not require agencies to use a “falsifiable” standard in the sense
that Cattle Growers uses the term. What Cattle Growers calls
“non-falsifiable” is simply the reality that differences in data
choices and study design influence the outcome of scientific
studies of empirical phenomena, including those applying the
non-clinal geographic variation standard. For instance, Cattle
Growers asserts that the “falsifiability problem is
demonstrated” by the fact that Zink and Theimer “came to
markedly different conclusions regarding non-clinal
geographic variation” depending on whether they chose to
“analyze[] either narrow (Theimer (2016)) or broad (Zink
(2017)) subsets of the southwestern willow flycatcher’s genetic
and morphological data.” Cattle Growers Br. 42.
Every scientific study, in fields ranging from ornithology
to oncology, suffers from what Cattle Growers sees as a
problem of “non-falsifiability.” It is elementary that a study’s
conclusions necessarily depend on the data that the study’s
authors gather and analyze, and the tools they use to analyze it.

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Indeed, a model that produces the same results regardless of
differences in its data inputs is of little use. But the fact that
study results are influenced by discretionary decisions
regarding data inputs and study design does not shield
researchers’ conclusions from scrutiny or invite agencies to
baselessly rely on shoddy studies. Rather, the peer review
process and the discipline provided by competing research
studies guard against cherry-picking or poor design by forcing
scientists to identify, explain, and submit for public scrutiny the
discretionary choices that are inevitable in research design. At
the same time, the APA’s prohibition on arbitrary and
capricious decision making, coupled with the Endangered
Species Act’s requirement that the Service make its
determinations “solely on the basis of the best scientific and
commercial data available,” 16 U.S.C. § 1533(b)(1)(A),
require the Service to “articulate a satisfactory explanation” as
to which studies represents the “best” scientific data. State
Farm, 463 U.S. at 43.
We reject Cattle Growers’ contention that the inherent
reliance of empirical analysis on data selection (and the
attendant risk of manipulation) changes the narrow
reasonableness standard imposed by the APA. The Service’s
thorough explanation of its determinations as to which studies
represented the best available data, as well as its explanation of
its conclusion that those studies supported subspecies
classification, comfortably meet the APA’s requirement that
agency action be “reasonable and reasonably explained.” FCC
v. Prometheus Radio Project, 592 U.S. 414, 423 (2021). Faced
with competing studies, the Service analyzed their strengths
and weaknesses point by point. It concluded that Theimer’s
reanalysis of the relevant data was more rigorous and thus more
persuasive than Zink’s because Zink’s conclusions drew on
incorrectly graphed data and analytical methods that were not
tailored to avian subspecies analysis. See Notice 18, 21 (J.A.

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592, 595). Based on its careful review, the Service concluded
that, according to the best available science, the subspecies
designation of the southwestern willow flycatcher should
stand. That determination is scientifically and legally sound.
Cattle Growers’ concern that the non-clinal geographic
variation standard leaves the regulated public and the courts
without a meaningful way to understand and evaluate the
Service’s decision making is unfounded. After determining
which studies represented the best available data, the Service
straightforwardly applied the non-clinal geographic variation
standard to discern that those studies, which provided evidence
of a “break” in plumage coloration and genetic markers
“consistent with a step cline,” supported subspecies
classification. Notice 17-18, 20-21 (J.A. 591-92, 594-95).
Cattle Growers’ own petition demonstrates that it understands
how the non-clinal geographic variation standard operates: Its
petition relied on that very standard to argue that gradual
differences in willow flycatchers’ genetic makeup and plumage
coloration across their range, as opposed to “sharp breaks,”
undermined subspecies classification. See, e.g., Petition 4-5,
17-19 (J.A. 493-94, 506-08). There is thus no merit to Cattle
Growers’ contention that the Service impermissibly relied on
an “unarticulated . . . standard” in violation of the APA. Cattle
Growers Br. 34 (quoting Pearson, 164 F.3d at 660). To the
contrary, the Service explicitly set forth the non-clinal
geographic variation standard, and it explained how that
standard informed its evaluation of the relevant data. See, e.g.,
Notice 9, 17, 20 (J.A. 583, 591.
Using the language of “non-falsifiability,” Cattle Growers
attempts to manufacture a more favorable standard for its
underlying disagreement with the Service’s determination that
Zink’s analysis was less rigorous and persuasive than that of
other scientific studies. Cattle Growers argues that the

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Service’s reliance on studies that “omitt[ed] intermediary data”
illustrates the “non-falsifiable” nature of the non-clinal
geographic variation standard, and that the Service’s use of
such a “non-falsifiable” standard necessarily makes the
Service’s decision arbitrary and capricious. Reply Br. 16-17;
see also Cattle Growers Br. 43-44. As explained above,
“falsifiability”—in the sense that Cattle Growers uses that
term—has nothing to do with whether an agency’s decision
was arbitrary and capricious. And it is firmly established that
the mere presence of “[c]ompeting views about scientific data
and policy choices” is insufficient to show that the agency
acted arbitrarily. Defs. of Wildlife v. Zinke, 849 F.3d 1077,
1089 (D.C. Cir. 2017). Particularly “when the science is
uncertain,” arbitrary and capricious review does not allow the
reviewing court to “direct the agency in a choice between
rational alternatives.” Shafer, 992 F.3d at 1090. Rather, the
court “simply ensures that the agency has acted within a zone
of reasonableness and, in particular, has reasonably considered
the relevant issues and reasonably explained the decision.”
Prometheus Radio Project, 592 U.S. at 423.
The Service’s decision not to delist the southwestern
willow flycatcher was reasonable, reasonably supported, and
adequately explained, and its decision as to what constitutes the
best available scientific evidence is well within its zone of
expertise. The Service set forth its definition of a subspecies;
explained how scientists operationalize that definition;
examined the relevant studies and rationally explained why it
found some more convincing than others; and reasonably
explained why it found the petition’s counterarguments
unpersuasive. That is all the ESA and APA require. We
therefore decline Cattle Growers’ invitation to “step into the
[agency’s] shoes and reassess its scientific judgments—a role
that we are ill-equipped to play under the guise of the APA’s
arbitrary and capricious standard.” Pharm. Mfg. Rsch. Servs.,

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Inc. v. Food & Drug Admin., 957 F.3d 254, 265 (D.C. Cir.
2020) (internal quotation marks omitted).
Cattle Growers further argues that allowing the Service to
rely on non-clinal geographic variation in making its
subspecies determination “raises serious nondelegation and
due process concerns, counseling that it be rejected pursuant to
the canon of constitutional avoidance.” Cattle Growers Br. 47.
That argument is forfeited by Cattle Growers’ failure to raise it
before the district court. Huron v. Cobert, 809 F.3d 1274, 1280
(D.C. Cir. 2016). It is also misdirected. Cattle Growers
invokes the concept of constitutional avoidance, but that is a
canon of statutory construction that “comes into play only
when, after the application of ordinary textual analysis, the
statute is found to be susceptible of more than one
construction.” Jennings v. Rodriguez, 583 U.S. 281, 296
(2018). This is a case brought under the APA’s arbitrary and
capricious action standard that does not involve statutory
construction. In fact, Cattle Growers did not make a statutory
construction argument at all until its appellate reply brief,
rendering this argument forfeited many times over. See N.Y.
Rehab. Care Mgmt., LLC v. NLRB., 506 F.3d 1070, 1076 (D.C.
Cir. 2007). Cattle Growers’ constitutional claims have no
place here.
Cattle Growers’ remaining arguments are contradicted by
the record. It asserts that the Service relied on the “majority
opinion” of scientists to affirm the validity of subspecies
classification for the southwestern willow flycatcher and
argues that such a “‘majority opinion’ standard is inherently
arbitrary.” Cattle Growers Br. 39-40. But the Service did not
rely on a “majority opinion” standard. The “majority opinion”
language that Cattle Growers quotes is not from the 2017
determination that it challenges, but from the original 1995
rule. Notice 12 (J.A. 586). In the 2017 determination—the

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only agency decision at issue here—the Service explained that
the large body of “peer-reviewed studies/reports and
conclusions by taxonomists” supporting subspecies
classification informed its determination that Zink’s outlier
analysis, which was “comprised of questionable analyses” and
reached inaccurate conclusions, did not represent the best
scientific evidence and thus did not warrant rescission of
subspecies classification. Id. at 24 (J.A. 598). The Service thus
did not merely “count[] academic heads,” as Cattle Growers
contends, Cattle Growers Br. 39; rather, it reasonably
considered Zink’s analysis in context with other studies as one
of many factors informing its evaluation of whether that paper
represented the best available evidence.
Last, Cattle Growers argues that, in the district court, the
Service incorrectly asserted that the Endangered Species Act’s
requirement that it base its determination on the “best scientific
and commercial data available” sufficed as a standard for
determining the validity of the southwestern willow
flycatcher’s subspecies classification. Cattle Growers Br. 50-
51; 16 U.S.C. § 1533(b)(1)(A). The Service made no such
assertion, either here or in the district court. Instead, as
explained above, the Service evaluated which sources
contributed to the best available evidence and applied the non-
clinal geographic variation standard to assess whether those
sources supported subspecies classification.
* * *
For the foregoing reasons, the district court’s judgment is
affirmed.
So ordered.

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