                       FOR PUBLICATION

    UNITED STATES COURT OF APPEALS
         FOR THE NINTH CIRCUIT

 AMERICAN WILD HORSE                            No. 18-17403
 CAMPAIGN; KIMERLEE
 CURYL,                                          D.C. No.
        Plaintiffs-Appellants,             3:18-cv-00059-LRH-
                                                   CBC
                  v.

 DAVID BERNHARDT,                                 OPINION
 Secretary of the Department
 of the Interior; MICHAEL D.
 NEDD; JILL C. SILVEY,
         Defendants-Appellees.


         Appeal from the United States District Court
                  for the District of Nevada
          Larry R. Hicks, District Judge, Presiding

             Argued and Submitted April 29, 2020
                  San Francisco, California

                          Filed July 2, 2020

       Before: Ronald Lee Gilman,* Susan P. Graber,
           and Daniel P. Collins, Circuit Judges.

                       Opinion by Judge Graber

    *
      The Honorable Ronald Lee Gilman, United States Circuit Judge for
the U.S. Court of Appeals for the Sixth Circuit, sitting by designation.
2        AM. WILD HORSE CAMPAIGN V. BERNHARDT

                            SUMMARY**


                             Wild Horses

    The panel affirmed the district court’s summary judgment
in favor of federal defendants in an action alleging that the
Bureau of Land Management (“BLM”)’s “geld and release”
plan for wild horses violated the National Environmental
Policy Act (“NEPA”), the Administrative Procedure Act, and
the Wild Free-Roaming Horses and Burros Act.

    BLM developed a Gather Plan to address an excess of
wild horses. In 2017, BLM determined that there was an
overpopulation of wild horses in northeastern Nevada. It
developed a plan to restore ecological balance by adjusting
the sex ratio of the population, administering fertility control
treatments to mares, and gelding and releasing back to the
range some male horses.

    The panel held that BLM did not act arbitrarily or
capriciously when it chose to geld and release some of the
male horses that would otherwise be permanently removed.
The panel rejected plaintiffs’ arguments challenging BLM’s
actions and decisions.

    Plaintiffs argued that BLM must prepare an
environmental impact statement (“EIS”) for its Gather Plan
because five of NEPA’s intensity factors demonstrated that
gelding and release would have significant effects on the
environment. First, an agency must prepare an EIS when its

    **
       This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                  3

action will have “highly uncertain effects” on the
environment. The panel held that BLM’s plan to geld and
release male horses to the range did not meet that threshold.
The panel held that BLM used the existing evidence to assess
the level of uncertainty and made reasonable predictions
based on prior data to conclude that there would be no
significant environmental impact. Second, the panel held that
the effects of the Gather Plan were not “highly controversial.”
Third, the panel held that the Gather Plan did not exhibit
“unique characteristics;” and BLM’s determination that the
gather area was not in close “proximity to historic or cultural
resources” was not arbitrary or capricious. Fourth, the panel
held that the Gather Plan did not establish a “precedent” for
future actions where the plan did not establish gelding as an
accepted population management tool, nor was it the first
instance of BLM’s releasing geldings to the range. Fifth, the
panel held that because BLM followed the mandates of the
Wild Free-Roaming Horses and Burros Act, its decision to
geld and release did not “threaten a violation of federal law.”
The panel concluded that BLM permissibly determined that
the intensity factors did not show that the Gather Plan would
have a significant effect on the environment, and BLM
permissibly concluded that preparation of an EIS was not
required.

    Plaintiffs argued that BLM acted arbitrarily and
capriciously because it did not address a Gelding Study, did
not consider the expert opinions that plaintiffs highlighted in
their public comments, and did not consider adequately a
National Academy of Sciences (“NAS”) Report on the wild-
horses program. First, the panel held that BLM met NEPA’s
“hard look” standard when it considered and addressed the
relevant factor that the Gelding Study raised and explained
why additional information was not available. Second, the
4      AM. WILD HORSE CAMPAIGN V. BERNHARDT

panel held that The Wild Free-Roaming Horses and Burros
Act did not require BLM to discuss explicitly all expert
opinions submitted during the public-comment period. Third,
the panel held that by addressing the concerns and factors that
the NAS Report raised, BLM complied with the Wild Free-
Roaming Horses and Burros Act’s requirement that BLM
“consult” the NAS to make determinations about how
appropriate management levels should be achieved.


                         COUNSEL

William N. Lawton (argued), Katherine A. Meyer, and
William S. Eubanks II, Eubanks & Associates LLC,
Washington, D.C., for Plaintiffs-Appellants.

Anna T. Katselas (argued), Devon Lea Flanagan, Daniela A.
Arregui, Holly A. Vance, Andrea L. Berlowe, and Mark R.
Haag, Attorneys; Eric Grant, Deputy Assistant Attorney
General; Jeffrey Bossert Clark, Assistant Attorney General;
Environment and Natural Resources Division, United States
Department of Justice, Washington, D.C.; Nancy Zahedi,
Assistant Regional Solicitor, Pacific Southwest Region,
United States Bureau of Land Management, United States
Department of the Interior, Sacramento, California; for
Defendants-Appellees.
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                  5

                         OPINION

GRABER, Circuit Judge:

    Public lands in the American West are home to thousands
of wild, free-roaming horses. Congress tasked Defendants,
the Secretary of the Department of the Interior and officials
from the Bureau of Land Management (“BLM”), with
preserving these “living symbols of the historic and pioneer
spirit of the West,” while also balancing the needs of other
wildlife and livestock that depend on the resources of public
lands. 16 U.S.C. § 1331. When wild horses become too
numerous for the land to support, Congress has mandated that
BLM remove excess horses until it reestablishes ecological
balance. Id. § 1333.

    In 2017, BLM determined that there was an
overpopulation of wild horses in northeastern Nevada, and it
developed a plan to restore ecological balance in the region.
In an effort to remove as few horses as possible, BLM plans
to adjust the sex ratio of the population, administer fertility
control treatments to mares, and geld and release back to the
range some male horses.

    Plaintiffs American Wild Horse Campaign and Kimerlee
Curyl objected to the “geld and release” component of the
plan and brought claims that BLM had violated the National
Environmental Policy Act (“NEPA”), the Administrative
Procedure Act, and the Wild Free-Roaming Horses and
Burros Act. We hold that BLM did not act arbitrarily and
capriciously and, accordingly, we affirm the district court’s
grant of summary judgment to Defendants.
6      AM. WILD HORSE CAMPAIGN V. BERNHARDT

                     BACKGROUND

    A. Statutory and Historical Background

    Congress enacted the Wild Free-Roaming Horses and
Burros Act (“the Act”) in 1971, when wild horses were “fast
disappearing from the American scene.” 16 U.S.C. § 1331.
The Act extended federal protection to wild horses and
empowered BLM to manage horses roaming public ranges as
part of its management of public lands. But within only a few
years, the Act proved so successful at replenishing the
population of wild horses that “action [was] needed to
prevent [the] program from exceeding its goals and causing
animal habitat destruction.” H.R. Rep. No. 95-1122, 95th
Cong., 2d Sess. at 23 (1978).

    In 1978, Congress amended the Act to increase BLM’s
authority to manage and remove excess horses from public
lands “to achieve and maintain a thriving natural ecological
balance.” 16 U.S.C. § 1333(a). The main purpose of the
amendments was “to cut back on the protection the Act
affords wild horses, and to reemphasize other uses of the
natural resources wild horses consume.” Am. Horse
Protection Ass’n v. Watt, 694 F.2d 1310, 1316 (9th Cir.
1982).

    The amended Act directs the agency to maintain an
inventory of wild horses on public lands so that it can
determine whether “an overpopulation exists on a given area”
and whether “action is necessary to remove excess animals.”
16 U.S.C. § 1333(b)(2). If BLM makes such a finding, the
agency “shall immediately remove excess animals from the
range so as to achieve appropriate management levels.” Id.
Removals must continue “until all excess animals have been
        AM. WILD HORSE CAMPAIGN V. BERNHARDT                   7

removed so as to restore a thriving natural ecological balance
to the range, and protect the range from the deterioration
associated with overpopulation.” Id. Although BLM must
remove excess horses when it faces an overpopulation, the
Act also grants BLM the authority to use other population
control methods, such as sterilization and natural controls, to
avoid overpopulation. Id. § 1333(b)(1); see In Def. of
Animals v. U.S. Dep’t of Interior, 751 F.3d 1054, 1065 &
n.16 (9th Cir. 2014) (noting that BLM has broad discretion in
removing excess animals). In deciding on appropriate
measures, BLM must consult with state wildlife agencies,
“individuals independent of Federal and State government as
have been recommended by the National Academy of
Sciences,” and others that BLM determines have “scientific
expertise and special knowledge.” 16 U.S.C. § 1333(b)(1).
And “management activities shall be at the minimal feasible
level.” Id. § 1333(a).

    In recent years, BLM regularly has had to remove, or
“gather,” horses from public lands to keep the population
within the appropriate management levels and to avoid the
degradation of rangeland resources and the suffering of wild
horses due to a lack of water and forage. Although the Act
allows excess horses to be adopted or euthanized, 16 U.S.C.
§ 1333(b)(2), adoption demand is insufficient to achieve
population control, and Congress effectively has prohibited
BLM from euthanizing healthy animals by prohibiting the
authorization of funds to do so. In Def. of Animals, 751 F.3d
at 1060 n.6. Instead, BLM keeps removed horses in long-
term holding facilities for the remainder of their natural lives.

   About a decade ago, to assist it in improving the wild-
horses program, BLM commissioned a report from the
National Academy of Sciences (“NAS Report”) “to provide
8       AM. WILD HORSE CAMPAIGN V. BERNHARDT

BLM with a scientific evaluation of the program’s pressing
challenges.” The report, issued in 2013, evaluated various
methods of population control. It recommended that BLM
consider “changes in expression of sexual and social
behavior” when deciding whether to sterilize horses and
noted that the “ideal method would not eliminate sexual
behavior or change social structure substantially.” The report
concluded that “the methods judged most promising for
application to free-ranging horses or burros are PZP vaccines,
GonaCon vaccine,1 and chemical vasectomy.” It noted,
however, that “testing [of chemical vasectomy] in captive
horses would be needed before widespread application in the
field.” As for gelding some males in a herd, the report
concluded that the effects on reproduction and behavior
“could not be predicted at the time [the] report was prepared.”
The report stated that it was not clear how gelding “would be
better than [surgical] vasectomy, which does not affect
testosterone or male-type behaviors,” but the report
recognized that there are some risks to herds associated with
surgical vasectomy as well.

    To gain a better understanding of gelding as a population-
control method and of its effects on herd behavior, BLM
began a five-year study in 2016 (“Gelding Study”). The
Gelding Study, conducted as part of a gather plan
implemented in Utah, will evaluate whether gelding is “an
effective approach to slowing the annual population growth
rate,” the effects “of maintaining a population of gelded
males on the behavior and spatial ecology of the overall
population,” and the “health and short-term survival” of the


    1
      PZP and GonaCon are immune-contraceptive vaccines. PZP
vaccines are administered to mares; GonaCon vaccines can be
administered to either male or female horses.
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 9

geldings. This is the first study that has examined
specifically “the effect of gelding on the behavior of free-
roaming wild horses” and the way in which geldings interact
with intact wild stallions. Data from the study will not be
analyzed until October 2020 at the earliest.

   B. The Present Controversy

    The Antelope and Triple B Complexes comprise about
2.8 million acres of public lands in northeastern Nevada and
are home to thousands of wild horses. More than a decade
ago, BLM established that those areas could sustain a total of
between 899 to 1,678 wild horses. In 2017, based on a
current inventory of the lands, BLM determined that the
Complexes contained an excess population of about 8,600
wild horses and that action was necessary to remove them.
Once BLM made that determination, the Act required BLM
to “immediately remove excess animals.” 16 U.S.C.
§ 1333(b)(2).

    BLM developed the Antelope and Triple B Complexes
Gather Plan (“Gather Plan”) to address the excess, while also
keeping its management activities to “the minimal feasible
level.” Under the Gather Plan, BLM will remove the excess
wild horses over a ten-year period. Horses will be gathered
in phases as necessary to achieve a core breeding population
at the low range of the appropriate management level. The
plan also calls for adjusting sex ratios and administering
fertility-control treatments to mares in order to slow
population growth rates and increase intervals between
gathers.

   In an effort to reduce the number of horses that need to be
removed permanently from public lands and kept in long-
10     AM. WILD HORSE CAMPAIGN V. BERNHARDT

term holding facilities, BLM will geld some male horses and
release them back onto the range “where they can engage in
free-roaming behaviors.” By doing so, BLM can reduce the
breeding population to the low end of the appropriate
management level, but keep the total population of horses at
mid-range. The primary purpose of the gelding component
is not to slow population growth, but to allow more horses to
remain free-roaming than otherwise would be possible.

    Gelding horses is a centuries-old practice. It has been
studied extensively and is a routine procedure. It also is one
of the few permanent fertility-control options, resulting in
fewer “handling occasions” compared to other impermanent
methods. The only unknown aspects of gelding—as
identified in the NAS Report and acknowledged by BLM in
the Gelding Study—concern how useful it proves to be as a
population-control method and how wild horses will respond
when geldings are released back to the range.

    In 2017, BLM issued a preliminary environmental
assessment of the Gather Plan. 40 C.F.R. § 1508.9. BLM
received almost 5,000 public comments. Public comments
notified BLM of the concerns of experts on wild-horse
behavior about the negative effects of gelding wild horses. In
the final environmental assessment, BLM responded to those
comments and explained that the experts’ opinions were
speculative because none of them had conducted a study on
the topic. BLM concluded that the Gather Plan would not
significantly affect the human environment and, thus, that
BLM was not required to prepare an environmental impact
statement (“EIS”). In December 2017, BLM issued a finding
of no significant impact.
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 11

    In this action, Plaintiffs challenge the “geld and release”
portion of the Gather Plan. Plaintiffs do not deny that there
are too many wild horses in the Complexes, that BLM is
required to address that overpopulation, that removal of some
horses from the range is appropriate, or that BLM established
appropriate management levels of wild horses for the
Complexes. Plaintiffs challenge only BLM’s choice to geld
and release some of the male horses that would otherwise be
permanently removed, arguing that the agency acted
arbitrarily and capriciously. The district court granted
summary judgment to Defendants on all claims. Plaintiffs
timely appeal.

                STANDARDS OF REVIEW

   We review de novo a district court’s grant of summary
judgment. McGinest v. GTE Serv. Corp., 360 F.3d 1103,
1112 (9th Cir. 2004).

    We review agency decisions that allegedly violate NEPA
under the Administrative Procedure Act, and we set aside
those decisions only if they are “arbitrary, capricious, an
abuse of discretion, or otherwise not in accordance with law.”
Native Ecosystems Council v. U.S. Forest Serv., 428 F.3d
1233, 1238 (9th Cir. 2005) (quoting 5 U.S.C. § 706(2)(A)).

    In reviewing an agency’s decision not to prepare an EIS,
we “employ an arbitrary and capricious standard that requires
us to determine whether the agency has taken a ‘hard look’ at
the consequences of its actions, based [its decision] on a
consideration of the relevant factors, and provided a
convincing statement of reasons to explain why a project’s
impacts are insignificant.” Envtl. Prot. Info. Ctr. v. U.S.
12      AM. WILD HORSE CAMPAIGN V. BERNHARDT

Forest Serv. (EPIC), 451 F.3d 1005, 1009 (9th Cir. 2006)
(alteration in original) (internal quotation marks omitted).

                       DISCUSSION

    Plaintiffs argue that BLM must prepare an EIS for the
Gather Plan because five of NEPA’s intensity factors
demonstrate that gelding and release would have significant
effects on the environment. Plaintiffs also argue that BLM
acted arbitrarily and capriciously because it authorized
gelding and release without considering all the relevant
evidence.

     A. Intensity Factors

    NEPA requires agencies to prepare an EIS for “major
Federal actions significantly affecting the quality of the
human environment.” 42 U.S.C. § 4332(c). To determine
whether an action will have significant effects, agencies may
prepare an environmental assessment that “[b]riefly
provide[s] sufficient evidence and analysis for determining
whether to prepare an [EIS].” 40 C.F.R. § 1508.9(a)(1). An
EIS is required if that process raises “substantial questions”
about whether an agency action will have a significant effect.
Blue Mountains Biodiversity Project v. Blackwood, 161 F.3d
1208, 1212 (9th Cir. 1998). If the agency determines that an
EIS is unnecessary, it issues a finding of no significant
impact, which “briefly present[s] the reasons why an action
. . . will not have a significant effect on the human
environment.” 40 C.F.R. § 1508.13.

    To determine whether an action “significantly” affects the
environment, agencies must consider both the “context” and
“intensity” of the possible effects. 40 C.F.R. § 1508.27.
        AM. WILD HORSE CAMPAIGN V. BERNHARDT                  13

“Intensity” refers to the “severity of impact,” and NEPA
regulations include ten intensity factors that agencies must
consider. Id. An action may be, but is not necessarily,
“significant” if any one of those factors is met. Ctr. for
Biological Diversity v. Nat’l Highway Traffic Safety Admin.,
538 F.3d 1172, 1220 (9th Cir. 2008).

    Plaintiffs argue that five intensity factors demonstrate that
the Gather Plan may have a significant impact: (1) the Plan
has highly uncertain effects; (2) the Plan has highly
controversial effects; (3) the area has unique characteristics;
(4) the decision establishes a precedent; and (5) the decision
threatens a violation of the Wild Free-Roaming Horses and
Burros Act. 40 C.F.R. § 1508.27(b)(3), (4), (5), (6), & (10).
We disagree.

        1. Highly Uncertain Effects

    When the possible effects of an agency’s action are so
“highly uncertain” that they raise “substantial questions”
about whether the action will have a significant impact on the
environment, the agency must prepare an EIS. 40 C.F.R.
§ 1508.27(b)(5); Blue Mountains, 161 F.3d at 1212. NEPA
“regulations do not anticipate the need for an EIS anytime
there is some uncertainty, but only if the effects of the project
are ‘highly’ uncertain.” Ctr. for Biological Diversity v.
Kempthorne, 588 F.3d 701, 712 (9th Cir. 2009) (internal
quotation marks omitted).

    BLM’s plan to geld and release male horses to the range
does not meet that threshold. Gelding horses is not a new
practice, and its effects are well understood.          The
environmental assessment thoroughly reviewed the research
on the surgical procedure, on the effects of gelding on
14     AM. WILD HORSE CAMPAIGN V. BERNHARDT

domesticated and semi-feral horses, on the effects of
castration on other species, and on the natural social behavior
of wild horses. In that discussion, BLM acknowledged that
wild horses “are rarely gelded and released back into the
wild, resulting in few studies that have investigated their
behavior in free-roaming populations.” Thus, BLM used the
existing research to predict that those effects likely would be
insignificant.

    Some “quotient of uncertainty . . . is always present when
making predictions about the natural world.” Id. And we
have upheld agency predictions despite some uncertainty. Id.
In Center for Biological Diversity, for example, we held that
the Fish and Wildlife Service made reasonable predictions,
based on prior data, about the effects of their regulation on
polar bears even though “the specter of climate change made
the Service’s prediction less certain than it would be
otherwise.” Id. That the agency did not have perfect
information and had to extrapolate did not make the possible
effects “highly uncertain” and did not require the preparation
of an EIS. Id.

    Similarly, in EPIC, 451 F.3d 1005, and Native
Ecosystems Council, 428 F.3d 1233, we upheld the
reasonableness of agency predictions in the face of some
uncertainty. In EPIC, the precise effects on spotted owls
could not be “accurately described without additional
information,” but we held that the agency permissibly
declined to prepare an EIS because the agency provided
reasons, based on the available research, for the assumptions
that it made and for the conclusion that it drew: the effects
likely would be minor. 451 F.3d at 1011 (internal quotation
marks omitted). We also did not fault the agency for not
preparing an EIS in Native Ecosystems despite imperfect
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 15

information and some evidence that the project would have
negative effects on wildlife. We explained that “the presence
of some negative effects [does not] necessarily rise[] to the
level of demonstrating a significant effect on the
environment.” 428 F.3d at 1240.

    The same general analysis applies here.            While
acknowledging that available research was not perfectly
analogous, BLM used the existing evidence to assess the level
of uncertainty and made “reasonable predictions on the basis
of prior data” to conclude that there would be no significant
environmental impact. Ctr. for Biological Diversity, 588 F.3d
at 712. BLM did not have to conclude that its project would
have no effect, but only that there were not substantial
questions as to whether gelding and release would have a
significant effect on the environment. Although the
environmental assessment did not always make BLM’s
reasoning explicit, we will “uphold a decision of less than
ideal clarity if the agency’s path may reasonably be
discerned.” Nat’l Ass’n of Home Builders v. Defs. of
Wildlife, 551 U.S. 644, 658 (2007) (internal quotation marks
omitted).

    Exactly what role geldings will play within the wild-horse
population when they return to the range is unknown, but
BLM reasonably concluded that there was no reason to
expect any behavioral change in individual geldings to be
significant. BLM explained that, although geldings might
exhibit some behavioral differences, they will still be free to
roam unhindered and will have “a number of biological
impulses” compelling them to do so. Male horses take on a
number of different roles during their lives, so a change in a
gelding’s behavior post-castration would not necessarily have
a significant or adverse effect because the gelding could fit a
16      AM. WILD HORSE CAMPAIGN V. BERNHARDT

natural role other than reproducing. BLM further concluded
that the effects of gelding on individual horses would not be
more significant than the effects of the alternative—
permanently removing those horses from public lands.

     BLM likewise considered the effects on family structures
among wild horses and reasonably concluded that there
would be no significant effects. BLM cited a study finding
that the presence of geldings did not disrupt relationships
between mares and foals. BLM further noted that the plan
will not geld a large enough number of males to substantially
reduce population growth rates. Because the number of
geldings will not be sufficient to affect reproductive patterns,
it is less likely that geldings would significantly affect other
family dynamics.

    BLM provided a scientific foundation for its assumptions
and predictions. We defer to an agency’s “scientific
prediction[s] within the scope of its technical expertise.” Ctr.
for Biological Diversity, 588 F.3d at 712. Nothing in the
record, and none of Plaintiffs’ objections, undermines the
reasonableness of BLM’s conclusion.

    Nor do our prior cases require a different result. In Bark
v. United States Forest Service, 958 F.3d 865, 869–71 (9th
Cir. 2020), we held that the Forest Service’s finding of no
significant effects was arbitrary and capricious because the
plaintiffs “pointed to numerous expert sources,” including
expert studies and research directly contrary to the agency’s
conclusion, and the agency failed to engage with that body of
research. By contrast, Plaintiffs have not identified any
evidence affirmatively showing that returning geldings to the
range would affect herd behavior. And BLM engaged with
the currently available scientific evidence either by discussing
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 17

the studies expressly or by addressing the concerns that the
research raised. See In Def. of Animals, 751 F.3d at 1072
(explaining that an agency must address crucial factors, but
not necessarily specific evidence regarding that factor).

    Plaintiffs point to the NAS Report as evidence of
potentially significant effects. But that report acknowledged
the dearth of applicable scientific evidence and was
ultimately inconclusive. The report explained that “male-
type aggressive and sexual behaviors are usually reduced” in
geldings but that the response varies by individual horse. It
concluded that whether gelding and release would “increase
aggression and competition in herds or decrease it” was
uncertain.

    Only one study of domestic horses found increased
aggression in geldings. But, as BLM noted, wild male horses
naturally have varying levels of testosterone and behavior
depending on a variety of factors. Some change in behavior
among released geldings, then, would not necessarily be
disruptive. And a single study does not per se suffice to
demonstrate highly uncertain effects. See In Def. of Animals,
751 F.3d at 1071 (finding that the effects of administering
PZP to horses were not “highly uncertain” despite two studies
discussing the possible negative effects of PZP on herd
behavior); Native Ecosystems, 428 F.3d at 1240 (“[T]he
presence of some negative effects [does not] necessarily rise[]
to the level of demonstrating a significant effect on the
environment.”).

   Finally, there was no other available information that
BLM should, or could, have used to reduce the uncertainty
about the effects of gelding and release. Data from BLM’s
Gelding Study will not be analyzed until later this year. And
18     AM. WILD HORSE CAMPAIGN V. BERNHARDT

the mere fact that BLM chose to study the effects of gelding
and release is not evidence that the effects on herd behavior
are highly uncertain or might be significant. The study will
provide information not only about the effects on herd
behavior, but also about the effectiveness of gelding as a
population control method. Because the Gather Plan’s use of
gelding was not primarily intended as a population control
tool, any uncertainty regarding gelding’s effect on population
growth is not significant. The Gelding Study reveals BLM’s
opinion that the effects on herd behavior are not fully
understood but does not suggest that BLM expects the effects
to be significant—or even that there will be an effect at all.

    For that reason, our decision in National Parks &
Conservation Ass’n v. Babbitt, 241 F.3d 722 (9th Cir. 2001),
abrogated on other grounds as recognized by Monsanto Co.
v. Geertson Seed Farms, 561 U.S. 139, 157 (2010), is
inapposite. In that case, although the effects of the proposed
action were uncertain to some extent, the scientific evidence
revealed definite adverse effects. Id. at 732. The uncertainty
was over the intensity of the effects, id., and “[n]o new
scientific developments [were] required in order to obtain the
requisite information,” id. at 735. Under those circumstances,
the preparation of an EIS could help decision-makers better
understand the effects of the project.

    Similarly, in Ocean Advocates v. United States Army
Corps of Engineers, 402 F.3d 846, 867 (9th Cir. 2005), we
identified evidence in the record that the agency’s action
would have an “unquestionably severe” effect on the
environment. We noted that the agency failed to collect
available data, conduct projection analyses, or provide a
“justification regarding why more definitive information
could not be provided.” Id. at 870–71 (internal quotation
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 19

marks omitted). Here, by contrast, the uncertainty is whether
gelding and release will have any effect at all on the behavior
of wild horses. BLM is not required to wait years before
taking action simply because an ongoing study might shine
light on an uncertainty that BLM reasonably predicts will be
minor or nonexistent.

    After a thorough review of the evidence that was
available, BLM made “reasonable predictions” about the
relevant area of uncertainty. Ctr. for Biological Diversity,
588 F.3d at 712. Where there was no evidence that there
would be an effect, BLM was not required to conduct
additional research or wait for the results of the Gelding
Study before moving forward with its proposed action. The
NAS Report’s inconclusive statements and a single study
about domestic geldings does not undermine BLM’s
reasonable prediction that gelding and release will have
insignificant effects on herd behavior. BLM’s conclusion,
then, that the likelihood of significant effects of gelding was
not so uncertain as to require an EIS was not arbitrary or
capricious. EPIC, 451 F.3d at 1009.

       2. Highly Controversial

    The effects of the Gather Plan are not “highly
controversial.” 40 C.F.R. § 1508.27(b)(4). The evidence that
Plaintiffs identify does not “cast[] serious doubt upon the
reasonableness of [the] agency’s conclusions.” Humane
Soc’y of U.S. v. Locke, 626 F.3d 1040, 1057 (9th Cir. 2010)
(internal quotation marks omitted). Plaintiffs have not
identified any evidence that contradicts BLM’s findings. The
NAS Report was inconclusive and reported no findings that
conflict directly with those in the environmental assessment.
The expert opinions that Plaintiffs cite were not based on
20     AM. WILD HORSE CAMPAIGN V. BERNHARDT

studies that those experts had conducted, and no existing
research supported their speculation. Mere opposition to an
action does not, by itself, create a controversy within the
meaning of NEPA regulations. Id. BLM considered and
addressed the existing literature in its environmental
assessment and provided reasoning for its conclusions. That
satisfies NEPA. See Native Ecosystems, 428 F.3d at 1240
(“Simply because a challenger can cherry pick information
and data out of the administrative record to support its
position does not mean that a project is highly controversial
. . . .”).

       3. Unique Characteristics

    BLM’s determination that the gather area is not in close
“proximity to historic or cultural resources” was not arbitrary
or capricious. 40 C.F.R. § 1508.27(b)(3). Wild horses are
not a cultural resource for purposes of NEPA. Congress,
through the Wild Free-Roaming Horses and Burros Act,
decided how wild horses should be managed and how the
effects of agency actions on those horses should be evaluated.
The Act states that wild horses will be considered “an integral
part of the natural system of the public lands,” 16 U.S.C.
§ 1331, and specifically instructs that they should be managed
“as components of the public lands” and as a part of a
“natural ecological balance.” Id. § 1333(a). A specific
statute, such as the Act’s directive as to how to manage wild
horses, governs over a general provision, such as NEPA.
Perez-Martin v. Ashcroft, 394 F.3d 752, 758 (9th Cir. 2005);
see City & Cty. of San Francisco v. U.S. Citizenship &
Immigration Servs., 944 F.3d 773, 800 (9th Cir. 2019) (“We
cannot see how a general provision in one statute constrains
an agency given a specific charge in a subsequent law.”).
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                21

       4. Precedent

    The Gather Plan does not establish “a precedent for future
actions with significant effects,” nor does it represent “a
decision in principle about a future consideration.” 40 C.F.R.
§ 1508.27(b)(6). The Gather Plan does not establish gelding
as an accepted population-management tool, nor is it the first
instance of BLM’s releasing geldings to the range. The
conclusions in the environmental assessment for the Gather
Plan are specific to the scientific evidence that is currently
available. Like most environmental assessments, the Gather
Plan’s environmental assessment is “highly specific to the
project and the locale.” In Def. of Animals, 751 F.3d at 1071.

       5. Threatens a Violation of Law

    Finally, because BLM has followed the mandates of the
Wild Free-Roaming Horses and Burros Act, its decision to
geld and release does not threaten a violation of federal law.
40 C.F.R. § 1508.27(b)(10). BLM adequately addressed the
relevant factors raised by the NAS Report and the expert
opinions submitted during the public comment period to
satisfy the requirements of the Act, as discussed in Parts B.2
and B.3, below.

    We conclude that BLM permissibly determined that the
intensity factors, whether considered individually or
collectively, did not show that the Gather Plan would have a
significant effect on the environment. Accordingly, BLM
permissibly concluded that preparation of an EIS was not
required.
22      AM. WILD HORSE CAMPAIGN V. BERNHARDT

     B. Authorization of Gelding and Release

    Plaintiffs also argue that BLM acted arbitrarily and
capriciously because it did not address the Gelding Study, did
not consider the expert opinions that Plaintiffs highlighted in
their public comments, and did not consider adequately the
NAS Report.

        1. Gelding Study

    BLM did not discuss at length its Gelding Study in its
environmental assessment for the Gather Plan; nor did it wait
to authorize gelding and release until it obtained data from
the Study. But BLM considered and addressed the relevant
factor that the Gelding Study raised and explained why
additional information was not available, which meets
NEPA’s “hard look” standard. In Def. of Animals, 751 F.3d
at 1072–73.

    BLM adequately considered the effect of releasing
geldings back to the range both on the geldings themselves
and on the rest of the wild-horse population. Because the
Gelding Study has not yet provided any new information on
the factor, it was reasonable for BLM not to mention that
study in the preliminary environmental assessment.
Nevertheless, after BLM received comments that more
research was needed on the effects of gelding, it included a
brief discussion of the Gelding Study in its final
environmental assessment, explaining that results would not
be available for several years. BLM thus adequately
explained why additional data was unavailable. Cf. Ocean
Advocates, 402 F.3d at 870–71 (finding an agency’s failure to
collect available data or provide a “justification regarding
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 23

why more definitive information could not be provided” was
arbitrary and capricious).

    The Gather Plan’s use of gelding also does not reflect an
unexplained inconsistency that would violate the
Administrative Procedure Act. See Humane Soc’y, 626 F.3d
at 1051 (concluding that an agency’s action was arbitrary and
capricious because the agency failed to explain inconsistent
factual findings). Plaintiffs argue that, in the environmental
assessment for the Gelding Study, BLM found that it needed
the results of that study before it could make informed
decisions about gelding wild horses. In Plaintiffs’ view,
because the Gather Plan included gelding and release without
explaining why BLM no longer deemed the Study’s results
necessary for informed decision-making, BLM acted
arbitrarily and capriciously.

    BLM made no such finding in its environmental
assessment for the Gelding Study. That document merely
acknowledged that some uncertainty remained regarding the
effects of gelding on wild horses and that additional
information could improve its decision-making. The
intention of the Gelding Study is to augment BLM’s
understanding of gelding, not to dictate its future conduct and
decisions. The Gather Plan similarly includes measures to
help improve BLM’s understanding of gelding and release:
BLM will monitor and observe the behavior of released
geldings to determine whether they are freely moving, how
they intermix with the breeding population, and if replacing
breeding mares with geldings can be an effective approach to
slowing the rate of population growth. Those plans are
consistent with BLM’s ongoing efforts to better understand
the effects of gelding, as described in the Gelding Study’s
environmental assessment. There was neither a change in
24     AM. WILD HORSE CAMPAIGN V. BERNHARDT

practice nor an inconsistency with previous findings that
BLM was required to explain.

       2. Expert Opinions

    The Wild Free-Roaming Horses and Burros Act does not
require BLM to discuss explicitly all expert opinions
submitted during the public-comment period. See 16 U.S.C.
§ 1333(b)(1) (requiring that the agency consult individuals
recommended by the National Academy of Sciences, but
leaving it to the Secretary’s discretion whether to consult
“other individuals” with “scientific expertise and special
knowledge”). In its response to the public comments, BLM
provided reasons for not relying on those experts’ opinions
and referred to portions of the environmental assessment that
addressed those experts’ substantive concerns. That is a
sufficient explanation for us to conclude that BLM’s choice
was not arbitrary or capricious. See In Def. of Animals,
751 F.3d at 1073 (noting that we do not require an agency to
“recite its reasons for relying on the studies cited in [an
environmental assessment] as opposed to the studies cited by
[a] comment” to show that the agency “performed the ‘hard
look’ required by NEPA”).

       3. National Academy of Sciences Report

    By addressing the concerns and factors that the NAS
Report raised, BLM complied with the Wild Free-Roaming
Horses and Burros Act’s requirement that BLM “consult” the
National Academy of Sciences to make determinations about
how appropriate management levels should be achieved.
16 U.S.C. § 1333(b)(1). The report concluded that “[t]he
effect that gelding a portion of the males in a herd would have
on reproduction and behavior could not be predicted at the
       AM. WILD HORSE CAMPAIGN V. BERNHARDT                 25

time this report was prepared.” BLM acknowledged that
uncertainty in the environmental assessment and discussed
the evidence of potentially adverse effects of gelding.

    The only concern that BLM did not address expressly was
the NAS Report’s discussion of vasectomy as an alternative
to gelding.      Public comments on the preliminary
environmental assessment brought this alternative to BLM’s
attention, but BLM did not address it in the final
environmental assessment, either. The NAS Report, though,
was ambivalent in its support of vasectomy, noting that
surgical vasectomy creates some risks to herds. And BLM’s
guidebook, which was included in the record, states that
vasectomies are not widely performed on stallions and that
additional research is needed to “perfect a safe technique”
and “demonstrate whether this approach will reduce
population growth rates”—reflecting a similar level of
uncertainty as with gelding.

    Because evidence in the record supports BLM’s choice of
gelding, and because we can discern the reasons for BLM’s
rejection of the alternative of surgical vasectomy, Nat’l Ass’n
of Home Builders, 551 U.S. at 658, BLM’s failure to respond
explicitly to the comments about vasectomies was not
arbitrary or capricious. See In Def. of Animals, 751 F.3d
at 1072 (noting that NEPA does not require an agency “to
address in detail the substance conveyed in every single
comment made on an [environmental assessment] to prove
that the agency ‘considered’ the relevant factors”).

   AFFIRMED.
