                FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


IDAHO WOOL GROWERS                      No. 14-35445
ASSOCIATION; AMERICAN SHEEP
INDUSTRY ASSOCIATION; PUBLIC               D.C. No.
LANDS COUNCIL; WYOMING WOOL             1:12-cv-00469-
GROWERS ASSOCIATION; CARLSON                 BLW
COMPANY, INC.; SHIRTS BROTHERS
SHEEP; COLORADO WOOL GROWERS
ASSOCIATION,                              OPINION
              Plaintiffs-Appellants,

                 v.

TOM VILSACK, in his official
capacity as the Secretary of the U.S.
Department of Agriculture; TOM
TIDWELL, in his official capacity as
the Chief of the U.S. Forest Service;
KEITH LANNOM, in his official
capacity as the Forest Supervisor of
the Payette National Forest; UNITED
STATES FOREST SERVICE,
                Defendants-Appellees,

THE WILDERNESS SOCIETY;
WESTERN WATERSHEDS PROJECT;
HELLS CANYON PRESERVATION
COUNCIL,
  Intervenor-Defendants–Appellees.
2           IDAHO WOOL GROWERS ASS’N V. VILSACK

           Appeal from the United States District Court
                     for the District of Idaho
          A. Wallace Tashima, District Judge, Presiding*

                   Argued and Submitted
              November 2, 2015—Portland, Oregon

                        Filed March 2, 2016

        Before: Raymond C. Fisher, Marsha S. Berzon, and
                 Paul J. Watford, Circuit Judges.

                    Opinion by Judge Berzon


                           SUMMARY**


                       Environmental Law

    The panel affirmed the district court’s summary judgment
in favor of the United States Forest Service in an action
challenging the Forest Service’s decision, made in response
to concerns regarding disease transmission to
immunologically vulnerable bighorn sheep, to close to
domestic sheep grazing approximately 70% of allotments on



    *
    A. Wallace Tashima, Circuit Judge, for the Ninth Circuit Court of
Appeals, sitting in the United States District Court, for the District of
Idaho, by designation.
  **
     This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
         IDAHO WOOL GROWERS ASS’N V. VILSACK                  3

which grazing had been permitted in the Payette National
Forest in Idaho.

    The panel held that, pursuant to the National
Environmental Policy Act environmental review process, any
error by the Forest Service in failing to consult the
Agricultural Research Service, a federal agency within the
U.S. Department of Agriculture, before preparing the final
supplemental impact statement and Record of Decision, was
harmless. The panel held that because the lack of
consultation did not prevent the Forest Service or the public
from considering information about the uncertainties in
transmission of disease from domestic to bighorn sheep, such
as the Agricultural Research Service would have offered, and
because information about the precise mechanisms of such
transmission was not a basis of the Forest Service’s decision,
no prejudice resulted from the lack of consultation.

    The panel also held that the Forest Service did not
otherwise act arbitrarily or capriciously or abuse its
discretion. Specifically, the panel held that the Forest Service
did not act arbitrarily or capriciously or abuse its discretion
by declining to supplement the final supplemental impact
statement. The panel also held that the Forest Service did not
act arbitrarily or capriciously or abuse its discretion in its
modeling used to analyze bighorn sheep home ranges and
movement, and the potential impacts of various management
alternatives.
4       IDAHO WOOL GROWERS ASS’N V. VILSACK

                        COUNSEL

William G. Myers III (argued) and Murray D. Feldman,
Holland & Hart LLP, Boise, Idaho, for Plaintiffs-Appellants.

Robert J. Lundman (argued) and David B. Glazer,
Environment & Natural Resources Division, U.S. Department
of Justice, Washington, D.C.; Sam Hirsch, Acting Assistant
Attorney General, U.S. Department of Justice, Washington,
D.C.; Heather Hinton-Taylor, Office of the General Counsel,
U.S. Department of Agriculture, Washington, D.C., for
Defendants-Appellees.

Lauren M. Rule (argued), Advocates for the West, Portland
Oregon; Jennifer R. Schemm, La Grande, Oregon, for
Intervenor-Defendants–Appellees.


                         OPINION

BERZON, Circuit Judge:

     Between the late 1800s and the early 1900s, the number
of bighorn sheep in North America declined dramatically,
falling from a high of 1.5 to 2 million individuals to
approximately 10% of that number. Scientists have generally
attributed the decline to over-harvesting, habitat loss,
competition for food, and disease transmission from domestic
sheep.

    In response to concerns regarding disease transmission to
immunologically vulnerable bighorn sheep, the Chief of the
U.S. Forest Service ordered further analysis of the effects of
grazing domestic sheep in the Payette National Forest of
        IDAHO WOOL GROWERS ASS’N V. VILSACK                  5

west-central Idaho (“Payette”). In response, the Forest
Service prepared a draft supplemental environmental impact
statement (“DSEIS”), an update to the DSEIS, and,
eventually, a final supplemental environmental impact
statement (“FSEIS”) and Record of Decision (“ROD”).
Concluding that there is a significant risk of fatal disease to
the small and insular populations of bighorn sheep in the
Payette, the Forest Service decided in the ROD to close to
domestic sheep grazing approximately 70% of the allotments
on which grazing had been permitted.

    The Idaho Wool Growers Association, other state and
national trade associations, and two sheep ranchers
(collectively, “Wool Growers”) challenged the Forest
Service’s decision, objecting to the Forest Service’s (1)
failure to consult the Agricultural Research Service (“ARS”),
a federal agency within the U.S. Department of Agriculture,
before preparing the FSEIS and ROD; (2) failure to
supplement the FSEIS and ROD in light of the publication in
2010 of a certain study of the transmission of disease from
domestic to bighorn sheep, the “Lawrence study”; and (3)
choice and use of particular models to evaluate the risk of
contact between domestic and bighorn sheep and the effects
of disease transmission from domestic to bighorn sheep. The
district court entered summary judgment in favor of the
Forest Service. Wool Growers appealed.

    We conclude that any error in failing to consult ARS was
harmless. As the Forest Service did not otherwise act
arbitrarily or capriciously or abuse its discretion, we affirm.
6       IDAHO WOOL GROWERS ASS’N V. VILSACK

                             I.

A. Background

    Bighorn sheep are currently found in two populations in
the Payette—one in Hells Canyon and the other in the Salmon
River Mountains. In approximately 1870, major die-offs of
bighorn sheep began to occur in the Salmon River Mountains.
The die-offs roughly coincided with the onset of wide-spread
grazing of domestic sheep in the Payette.

    Over the years, the Payette’s bighorn populations have
continued to experience periodic “large-scale, rapid, all-age
die-offs.” FSEIS xx; see also ROD 6–7. Since 1981, despite
efforts at transplanting sheep from elsewhere, the total
population in the Payette has decreased by 47%. Although at
one time more than 10,000 bighorn sheep lived in Hells
Canyon and the surrounding mountains, “they were extirpated
by the mid-1940s.” ROD 6. Between 1971 and 2004, 474
bighorn sheep were transplanted into Hells Canyon. Seven
die-offs in the Hells Canyon population have been reported
since 1971. At the time the FSEIS was written, that
population numbered 850 sheep.

   The Salmon River population was never extirpated.
According to surveys in 2001, 2003, and 2004, that
population numbers roughly 700 sheep.

B. The NEPA Environmental Review Process

    The administrative process underlying this appeal began
in 2003, when the Forest Service, pursuant to the National
Environmental Policy Act (“NEPA”), issued the Southwest
Idaho Ecogroup Land and Resource Management Plans Final
        IDAHO WOOL GROWERS ASS’N V. VILSACK                  7

Environmental Impact Statement and Record of Decision
(“EIS”), which revised the 1988 Payette National Forest Land
and Resource Management Plan. The EIS was appealed,
appellants urging that the EIS “violated the [National Forest
Management Act] and Hells Canyon National Recreation
Area (HCNRA) Act on the Payette National Forest by
providing for grazing of domestic sheep within or near the
range of bighorn sheep, thus threatening the viability of
bighorn sheep though [sic] disease transmission.” ROD 1. In
March 2005, the Chief of the Forest Service agreed that the
EIS “did not adequately address viability [of bighorn sheep
populations in the Payette] or the potential for disease
transmission.” Id. The Chief therefore rejected the EIS’s
analysis.

    The Chief then “instructed the Regional Forester to
reanalyze the potential impacts of domestic sheep grazing on
bighorn sheep viability on the Payette National Forest to
ensure habitat is available to support a viable population of
bighorn sheep.” ROD 1. The Chief’s decision reflected
general concerns regarding disease transmission—in
particular, the spread of various strains of pneumonia-causing
or -contributing bacteria—from domestic to bighorn sheep, as
confirmed by anecdotal evidence and a multitude of studies.

     There is uncertainty regarding the particular mechanics of
disease transmission, and the evidence of transmission is
largely circumstantial. Pneumonia-causing bacteria are
commonly found in domestic sheep, with the worst outbreaks
killing 2.5% of domestic sheep in a herd. The impact of
pneumonia on bighorn sheep is considerably more
catastrophic. Episodic pneumonia outbreaks appear to be the
current limiting factor in bighorn sheep abundance and
distribution, both because large-scale die-offs caused by
8       IDAHO WOOL GROWERS ASS’N V. VILSACK

pneumonia kill most or all of a given population, and because
female bighorns who survive die-offs experience low
reproduction and high lamb mortality rates for years
following an outbreak. Consequently, a number of state and
federal agencies with jurisdiction over bighorn sheep have
expressed concern and modified their management plans to
address disease transmission from domestic to wild sheep.
ROD 6; see, e.g., John Beecham et al., Rocky Mountain
Bighorn Sheep (Ovis Canadensis): A Technical Conservation
Assessment, Feb. 12, 2007; Timothy Schommer & Melanie
Woolever, A Review of Disease Related Conflicts Between
Domestic Sheep and Goats and Bighorn Sheep, 2008;
Montana Department of Fish, Wildlife and Parks, Montana
Bighorn Sheep Conservation Strategy, Draft, August 2009;
Idaho Department of Fish & Game, Draft Bighorn Sheep
Management Plan, May 2010. As the FSEIS explained,
“[s]cientists from both sides of the issue . . . recommend that
the species be kept separate until the disease transmission
science is better understood.” ROD 11.

    In September 2008, the Forest Service released the
DSEIS, which “proposed to modify, delete, and add to the
current Forest Plan direction in response to the Chief’s
instructions.” ROD 1. The DSEIS precipitated over 14,000
public comments.

    In 2009, because of declining bighorn sheep numbers, the
Forest Service designated bighorn sheep a sensitive species
in the Intermountain Region, which includes the Payette.
Under that designation, the objectives of bighorn
management “are to prevent listing under the Endangered
Species Act (ESA), avoid or minimize impact to [the]
species[,] whose viability has been identified as a concern,
maintain viable populations of [the] species, and to develop
        IDAHO WOOL GROWERS ASS’N V. VILSACK                  9

and implement management objectives for [the species’]
populations and habitat.” ROD 8.

    The Forest Service released an update to the DSEIS in
January 2010, which “provided interested stakeholders and
the public an opportunity to review and comment on
improved analyses and alternatives.” ROD 1. In the update,
the Forest Service responded to criticisms of the DSEIS’s
qualitative analysis by providing a quantitative analysis. See
FSEIS xvii; e.g., A-85. That analysis used modeling to study
the potential risks and effects of contact and disease
transmission. More than 11,000 comments on the update to
the DSEIS were submitted.

    In July 2010, the Forest Service completed and released
the FSEIS and ROD. To analyze the effects of various
alternative plans on the Payette’s bighorn sheep, the Forest
Service used three models developed in conjunction with
researchers at the University of California, Davis Center for
Animal Disease Modeling and Surveillance. The models—
called the source habitat, risk of contact, and disease
models—incorporated telemetric location data, including
more than 54,000 data points collected in the Payette over the
course of twelve years from over 400 radio-collared bighorn
sheep. Even with the use of these models, the Forest Service
recognized, “[d]etermining the probability that a bighorn
sheep will reach an occupied [domestic sheep grazing]
allotment [in the Payette] and that contact between the
species will result in disease transmission is problematic,”
and “there is . . . essentially no research that would allow []
estimation” of the likelihood of contact causing disease
transmission. ROD 12. To account for that difficulty, the
Forest Service ran the disease model using a range of
probabilities of contact resulting in disease transmission—
10      IDAHO WOOL GROWERS ASS’N V. VILSACK

5%, 10%, 25%, 50%, 75%, and 100%. This approach
allowed the Forest Service to assess the effects of various
management alternatives on bighorn sheep subpopulations
despite its inability to estimate accurately the degree of risk
of disease-conveying contact.

     After applying the models, the Forest Service selected one
of the alternatives analyzed in the FSEIS, Alternative 7O.
Alternative 7O would result in the termination of domestic
sheep grazing on approximately 69,000 acres in the Payette,
with implementation to occur over three years. The models
showed that this alternative reduced the risk of extirpation of
all but one of the bighorn subpopulations to low-to-moderate
at the 5% transmission level; the models predicted a 100%
likelihood of extirpation of the Sheep Mountain
subpopulation at all transmission levels, due to that
subpopulation’s demographics and proximity to domestic
sheep grazing allotments. At the higher transmission levels,
the probabilities of extirpation under Alternative 7O ranged
from 4% to 76%. Ultimately, the Forest Service found that
large distances between domestic and bighorn sheep are
necessary to assure protection of bighorns from disease, as
bighorn sheep travel long distances across rugged terrain;
domestic sheep are known to stray from their herds,
remaining on allotments at unpermitted times; and bighorn
and domestic sheep are attracted to each other and seek out
each other’s company.

   The FSEIS incorporated findings from the then-
unpublished Lawrence study, the first experiment to
demonstrate directly that transmission of bacteria from
domestic to bighorn sheep is implicated in causing
pneumonia in bighorn sheep. The study’s authors extracted
bacteria from domestic sheep, genetically modified the
         IDAHO WOOL GROWERS ASS’N V. VILSACK                 11

bacteria to be antibiotic resistant and to radioactively
fluoresce (that is, give off light). The domestic sheep were
then inoculated with the modified bacteria. The domestic
sheep were initially placed in pens separated by ten meters
from pens of bighorn sheep. Later, they were moved so that
they were separated only by a fence. Still later, all the sheep
were commingled in a single pen.

    By the end of the study, three of the four bighorn sheep
had contracted pneumonia and died, and the fourth was
euthanized after displaying telltale and severe signs of
pneumonia. Post-mortem examinations of the bighorn sheep
showed that they carried the radioactively-labeled, antibiotic-
resistant bacteria with which only the domestic sheep had
been inoculated.

C. This Litigation

    Wool Growers appealed the ROD and FSEIS to the
Intermountain Regional Forester. During the appeal process,
Dr. Donald Patrick Knowles, a co-author of the Lawrence
study and a research scientist within ARS, submitted a letter
discussing his interpretation of the study’s results (“Letter”).
Dr. Knowles maintained that (1) the study did not prove that
fence-line contact between domestic and bighorn sheep
resulted in transmission of pneumonia-causing bacteria
between the species; (2) transmission of a disease-causing
organism, as well as the mechanisms of disease, are complex
processes; and (3) “transmission of an organism doesn’t
necessarily lead to disease.” Letter 1–2. The Regional
Forester, having considered Dr. Knowles’ input, denied Wool
Growers’ appeal.
12        IDAHO WOOL GROWERS ASS’N V. VILSACK

    Wool Growers then filed a complaint for declaratory and
injunctive relief in the district court, challenging the Forest
Service’s decision. The court granted Intervenors, a group of
environmental organizations, leave to enter the action as
defendants. Wool Growers moved to expand the record
pursuant to Asarco, Inc. v. U.S. EPA, 616 F.2d 1153 (9th Cir.
1980).1 The district court granted the motion, permitting the
parties to submit expert declarations in support of their cross-
motions for summary judgment. After a hearing, the district
court entered summary judgment in favor of the Forest
Service and Intervenors and dismissed the action.

    Wool Growers timely appealed the district court’s
decision. On appeal, Wool Growers challenges three aspects
of the Forest Service’s decision under NEPA: its (1) failure
to consult ARS prior to completing the FSEIS; (2) failure to
supplement the FSEIS; and (3) choice and use of models.

                                  II.

    NEPA is a purely procedural statute; it does not impose
any substantive requirements on an agency undertaking
environmental review. Lands Council v. McNair, 537 F.3d
981, 1000 (9th Cir. 2008) (en banc), overruled on other
grounds by Winter v. Nat. Res. Def. Council, Inc., 555 U.S. 7,
20 (2008). Rather, “NEPA aims to make certain that the
agency will have available, and will carefully consider,
detailed information concerning significant environmental
impacts, and that the relevant information will be made
available to the larger public audience.” Id. (citation and


 1
   Under Asarco, an administrative record can be expanded upon review
by a federal court to explain what’s already in the record but not to add
substantive evidence. 616 F.2d at 1159–60.
        IDAHO WOOL GROWERS ASS’N V. VILSACK                13

alterations omitted). Accordingly, federal agencies must
“take a ‘hard look’ at the environmental consequences of
their actions by preparing an EIS for each ‘major Federal
action significantly affecting the quality of the human
environment.’” Id. at 1000–01 (alteration omitted) (quoting
42 U.S.C. § 4332(2)(C)). An EIS “must ‘provide [a] full and
fair discussion of significant environmental impacts’ so as to
‘inform decisionmakers and the public of the reasonable
alternatives which would avoid or minimize adverse impacts
or enhance the quality of the human environment.’” Id. at
1001 (quoting 40 C.F.R. § 1502.1).

    Under NEPA and the Administrative Procedure Act
(“APA”), our review is limited to determining whether the
Forest Service’s analysis was “arbitrary, capricious, an abuse
of discretion, or otherwise not in accordance with law.” Id.
at 987 (quoting 5 U.S.C. § 706(2)(A)). We conclude that
although the Forest Service may have acted contrary to
NEPA in one respect, any such error was harmless. The
Forest Service did not otherwise act arbitrarily or
capriciously, nor did it abuse its discretion.

A. Consultation

   1. Duty to consult

    NEPA imposes on federal agencies conducting
environmental review a duty to consult with certain other
agencies. “Prior to making any detailed statement, the
responsible Federal official shall consult with and obtain the
comments of any Federal agency which has jurisdiction by
law or special expertise with respect to any environmental
impact involved [in the proposed action].” 42 U.S.C.
§ 4332(2)(C). Further, to promote NEPA’s policies of public
14        IDAHO WOOL GROWERS ASS’N V. VILSACK

participation and informed decisionmaking, copies of the EIS
and comments thereon from other agencies “shall accompany
the proposal through the existing agency review processes.”
Id.

    The regulations implementing these provisions state that
“[a]fter preparing a draft environmental impact statement and
before preparing a final environmental impact statement the
agency shall . . . [o]btain the comments of any Federal agency
which has jurisdiction by law or special expertise with respect
to any environmental impact involved . . . .” 40 C.F.R.
§ 1503.1(a)(1); see also id. § 1500.1(b) (“Accurate scientific
analysis, expert agency comments, and public scrutiny are
essential to implementing NEPA.” (emphasis added)).
“Special expertise” is defined as “statutory responsibility,
agency mission, or related program experience.” Id.
§ 1508.26. Under the statute and its implementing
regulations, the Forest Service may have had a duty to consult
with ARS before issuing the FSEIS.

    The pivotal question is whether ARS has “special
expertise” concerning one significant aspect of the proposed
decision, the mechanics of pathogen transmission in domestic
sheep.2 Wool Growers argues that it does. They note, for
example, that 7 C.F.R. § 2.65 delegates to ARS, among other
matters, the authority to “[c]onduct research concerning
domestic animals and poultry, their protection and use, [and]
the causes of contagious, infectious, and communicable
diseases.” Also, ARS’s mission statement proclaims: “ARS


   2
     Because we decide that any consultation error was harmless, see
section II.A.2., infra, we do not address the Forest Service’s argument that
the “special expertise” question does not apply to Dr. Knowles as an
individual.
        IDAHO WOOL GROWERS ASS’N V. VILSACK                 15

conducts research to develop and transfer solutions to
agricultural problems of high national priority and provide
information access and dissemination to . . . enhance the
natural resource base and the environment . . . .” U.S.
Department of Agriculture, Agricultural Research
Service, ARS: About US, http://www.ars.usda.gov/aboutus/
aboutus.htm.

    The Forest Service argues, in response, that it had no duty
to consult with ARS because that agency has no expertise in
wildlife management. Although ARS’s expertise does center
on domestic, not wild, animals, the development within and
movement of pathogens in domestic sheep is of some
relevance to concerns regarding disease transmission to
bighorn sheep. The Forest Service’s assessment of the
pertinence of that expertise may be too narrow an
interpretation of its consultation duty under NEPA. And the
language establishing NEPA’s consultation requirement is
expansive. It mandates consultation with any federal agency
that has “special expertise with respect to any environmental
impact involved.” 42 U.S.C. § 4332(2)(C) (emphasis added).
See also 40 C.F.R. § 1503.1(a)(1) (“[T]he agency shall . . .
[o]btain the comments of any Federal agency which has
jurisdiction by law or special expertise with respect to any
environmental impact involved . . . .” (emphasis added)).

    Further, Warm Springs Dam Task Force v. Gribble
suggests that for the consultation requirement to apply, the
particular expertise of an agency does not have to encompass
the proposed project as a whole or the issue the proposed
project was designed to address. Rather, the expertise need
relate only to one of the project’s anticipated environmental
effects. See 621 F.2d 1017, 1020–21 (9th Cir. 1980) (per
curiam).
16       IDAHO WOOL GROWERS ASS’N V. VILSACK

    In the end, we need not resolve in this case the precise
parameters of the consultation requirement, or whether it
extended to ARS on the record before us. Any violation of
the consultation duty that occurred here, we are persuaded,
was harmless.

     2. Prejudice

    The APA directs us to take “due account . . . of the rule of
prejudicial error.” 5 U.S.C. § 706; see Nevada v. Dep’t of
Energy, 457 F.3d 78, 90 (D.C. Cir. 2006). Accordingly, we
consider whether the Forest Service’s failure to consult was
harmless. See Warm Springs, 621 F.2d at 1022–23. The
harmless-error analysis asks whether the failure to consult
materially impeded NEPA’s goals—that is, whether the error
caused the agency not to be fully aware of the environmental
consequences of the proposed action, thereby precluding
informed decisionmaking and public participation, or
otherwise materially affected the substance of the agency’s
decision. See Tucson Herpetological Soc. v. Salazar, 566
F.3d 870, 880 (9th Cir. 2009).

     Here, Wool Growers contends that, had consultation
occurred, ARS and Dr. Knowles would have conveyed to the
Forest Service information regarding the uncertainties of
disease transmission mechanisms from domestic sheep and
other contributors to bighorn disease. It is fair to assume Dr.
Knowles would have offered this information—he did offer
it to the Forest Service, both in his letter on appeal to the
Forest Supervisor, as well as in his declarations in the
expanded record before the district court. But, as reflected in
the FSEIS, such information had already been amply
communicated, and the Forest Service and the public already
had considered it.
        IDAHO WOOL GROWERS ASS’N V. VILSACK                 17

   For example, the FSEIS acknowledged:

       Some of these contentions [challenging the
       link between disease in domestic sheep and
       disease in bighorn sheep] are accurate. We do
       not understand all of the mechanisms involved
       in potential disease transmission between the
       species. . . . Arguably, much of the evidence
       is circumstantial; however, the compilation of
       cases throughout several decades does
       contribute to an increasing body of evidence
       that overwhelmingly demonstrates bighorn
       sheep near domestic sheep are at risk for
       disease transmission, even though “contact”
       may not have actually been observed.

FSEIS xxi. The FSEIS also specifically acknowledged
comments by “scientists and others, primarily from
agricultural disciplines,” regarding the effect of stressors on
bighorn sheep disease, as well as uncertainties regarding
disease transmission. Id. at 3-12–3-14. And in the ROD, the
Forest Supervisor took those views and comments into
consideration, stating: “Some scientists and others, primarily
from agricultural disciplines, contend that disease
transmission between bighorn sheep and domestic sheep is
not a relevant factor in bighorn sheep distribution and
population declines in the wildland environment. I have
taken these arguments into consideration while making my
decision.” ROD 11.

    Nor did these concerns escape public comment. The
public provided extensive comments showing awareness of
these considerations, including the comments that: “The
FSEIS should be particularly thorough when assessing the
18      IDAHO WOOL GROWERS ASS’N V. VILSACK

literature on the causal relationship of disease transmission
between domestic sheep and bighorn sheep,” FSEIS A-81;
“[e]vidence linking disease outbreaks to domestic sheep is
inconclusive,” “[s]tudies documenting disease transmission
between the two species have been done in controlled
environments,” and “[s]tress could be a precursor to the onset
of sickness”, id. at A-87; and “[t]he Forest Service should
disclose plans for reduction or elimination of stressors, such
as bad weather or lack of nutrition, that can predispose
bighorn sheep to disease or exacerbate risk of mortality,” id.
at A-186.

    In Warm Springs, we found no prejudice arising from the
Army Corps of Engineers’ failure to consult the U.S.
Geological Survey because the Corps subsequently
considered the study that consultation would have revealed.
See 621 F.2d at 1023. Similarly here, the Forest Service’s
failure to consult did not prejudice its review process. The
Forest Service took into account essentially the same
comments—arguments from “scientists and others, primarily
from agricultural disciplines” contesting the inference that
domestic sheep can and do transmit disease to wild bighorn
sheep—that ARS, through Dr. Knowles, would have provided
by formally consulting with the Forest Service during the
environmental review process.

    The Forest Service’s failure to consult ARS is immaterial
for another reason as well. The precise mechanisms of
disease transmission did not affect the Forest Service’s
decision. As the FSEIS states: “The exact means by which
the disease is transferred [from domestic to bighorn sheep] is
beyond the scope of this analysis and should be conducted by
qualified researchers.” FSEIS A-187. The FSEIS’s
conclusion was that the scientific consensus is that disease
        IDAHO WOOL GROWERS ASS’N V. VILSACK                 19

transmission from domestic sheep—by whatever mechanism
and involving whatever confounding factors—poses a
sufficient risk to bighorn sheep viability to merit separation
of the bighorns from the domestic animals. Confirming that
conclusion, numerous agencies with jurisdiction over bighorn
sheep have found the risk significant enough to compel
modification of their management plans. See section I.B.,
supra.

    Because the lack of consultation did not prevent the
Forest Service or the public from considering information
about the uncertainties in transmission of disease from
domestic to bighorn sheep such as ARS would have offered
(and which Dr. Knowles later did offer), and because
information about the precise mechanisms of such
transmission was not a basis of the Forest Service’s decision,
no prejudice resulted from the lack of consultation.

    Wool Growers maintains that its member wool companies
were prejudiced—some of them went out of business due to
the Forest Service’s ultimate decision, they claim. But this is
not the type of prejudice with which NEPA is concerned.
Rather, the question is whether the failure to consult
somehow materially altered the environmental review
process, not whether a constituent body was harmed by the
agency’s ultimate decision. See Cnty. of Del Norte v. United
States, 732 F.2d 1462, 1466–67 (9th Cir. 1984). Almost
invariably, some individuals or entities are negatively
affected by an agency decision. As long as “[t]he integrity of
the decision making process within the government and the
public’s opportunity to comment in accordance with all legal
20        IDAHO WOOL GROWERS ASS’N V. VILSACK

requirements were not compromised in any way,” id., there
is no prejudice of the sort with which NEPA is concerned.3

   Accordingly, we conclude that any error arising from the
Forest Service’s failure to consult was harmless.

B. Supplementation

    Wool Growers next challenges the Forest Service’s
failure to supplement the FSEIS. “Agencies . . . [s]hall
prepare supplements to either draft or final environmental
impact statements if . . . [t]here are significant new
circumstances or information relevant to environmental
concerns and bearing on the proposed action or its impacts.”
40 C.F.R. §1502.9(c). But “an agency need not supplement
an EIS every time new information comes to light after the
EIS is finalized.” Marsh v. Or. Nat. Res. Council, 490 U.S.
360, 373 (1989). So requiring “would render agency
decisionmaking intractable, always awaiting updated
information only to find the new information outdated by the
time a decision is made.” Id. Thus, only “if the new
information is sufficient to show that the remaining action
will affect the quality of the human environment in a
significant manner or to a significant extent not already
considered, [must] a supplemental EIS . . . be prepared.” Id.
at 374 (alteration and citation omitted).

  3
    The Forest Service also argues that any prejudice was cured by the
thorough vetting in the district court of disease transmission questions, as
expressed in the parties’ expert declarations. This extra-record evidence
does not cure the prejudice—the question of harmlessness is as to the
effect of an error on the NEPA process. The expert declarations were
submitted well after the NEPA process was complete. They cannot,
therefore, cure any prejudice, although they are informative as to whether
prejudice occurred.
          IDAHO WOOL GROWERS ASS’N V. VILSACK                       21

    Here, Wool Growers contends that publication of the
Lawrence study in 2010, after the FSEIS issued, triggered the
Forest Service’s duty to supplement. But: (1) the Forest
Service cited and discussed the study, in unpublished form,
numerous times in the FSEIS; (2) the study bolstered the
Forest Service’s decision by confirming that pneumonia-
linked bacteria were transmitted from domestic to bighorn
sheep, and that the transmitted bacteria likely caused the
pneumonia that killed the bighorns in the study;4 and (3) the
study, while confirming bacterial transmission between the
species in a manner not yet definitively proven, reaffirmed
the scientific consensus regarding the risk domestic sheep
present to bighorn sheep, as discussed in the FSEIS and ROD.

     The FSEIS stated, for example, that “the vast majority of
literature supports the potential for disease transmission
between the species, documents bighorn die-offs near
domestic sheep, and supports the management option of
keeping these species separate to prevent disease
transmission.” FSEIS 3-14. The Lawrence study was fully
in accord with the literature reported, and indeed was taken
into account by the FSEIS in making that statement. See id.
It was eminently reasonable for the Forest Service to
determine that the publication of the Lawrence study in
essentially the form relied upon in the FSEIS did not provide
significant information not already considered.

     Wool Growers also argues that the Forest Service should
have supplemented the FSEIS in light of Dr. Knowles’
critiques of the Lawrence study. But Dr. Knowles’ critiques


 4
    Wool Growers has not argued that the published version of the study
differs materially from the unpublished form to which the FSEIS cited,
and the Forest Service maintains there is no material difference.
22       IDAHO WOOL GROWERS ASS’N V. VILSACK

either: (1) conflict with the express findings of the study, of
which he was an author; or (2) state once more his views
regarding the lack of certainty in disease transmission
mechanisms. As to the former, it was reasonable for the
Forest Service to decide that certain of Dr. Knowles’
comments—which contradict the study’s conclusion that its
“results unequivocally demonstrate transmission of M.
haemolytica from domestic to bighorn sheep, resulting in
pneumonia and death of bighorn sheep”—did not represent
“significant” new information. The responses from other
authors of the Lawrence study disputed Dr. Knowles’
characterization of the results of the study, indicating that the
Forest Service reasonably concluded that Dr. Knowles’
critiques did not undermine the relevance of the study’s
conclusion. And as to the latter, the Forest Service could
reasonably have decided that Dr. Knowles’ comments
regarding the unproven and unknown mechanisms of disease
transmission were already well addressed in the FSEIS, as
discussed above, and therefore that his additional comments
to the same effect did not trigger its duty to supplement the
FSEIS. Supplementation is not required where the agency,
having taken a “hard look” at reevaluation, “determines that
the new impacts will not be . . . significantly different from
those already considered.” N. Idaho Cmty. Action Network v.
U.S. Dep’t of Transp., 545 F.3d 1147, 1154–55 (9th Cir.
2008) (per curiam).

   We conclude that the Forest Service did not act arbitrarily
or capriciously or abuse its discretion by declining to
supplement the FSEIS.
        IDAHO WOOL GROWERS ASS’N V. VILSACK               23

C. Models

   Wool Growers’ final challenge is to the modeling the
Forest Service used to analyze bighorn sheep home ranges
and movement, and the potential impacts of various
management alternatives.

     The framework for evaluating such challenges is well-
established. “Agencies [must] insure the . . . scientific
integrity[] of the discussions and analyses in environmental
impact statements.” 40 C.F.R. § 1502.24. Moreover, “NEPA
requires that [EISs] contain high-quality information and
accurate scientific analysis.” Lands Council v. Powell, 395
F.3d 1019, 1031 (9th Cir. 2005) (citing 40 C.F.R.
§ 1500.1(b)). If relevant data is incomplete or unavailable,
the EIS “must disclose this fact.” Id. Thus, when an agency
uses models in its NEPA analysis, it must provide “up-front
disclosures of relevant shortcomings in the data or models.”
Id. at 1032. When an agency undertakes technical scientific
analyses, as with the development of models to help analyze
a problem, the court’s deference to the agency’s judgment is
at its peak. Lands Council, 537 F.3d at 993.

   1. Risk of contact model

    The first model with which Wool Growers takes issue is
the risk of contact model. Wool Growers argues that model
failed adequately to take into account obstacles to bighorn
sheep mobility, including rivers and mountains.

    The Forest Service used one aspect of the risk of contact
model—the core herd home range analysis—to map the home
ranges for the fifteen herds in the Payette, as well as one
“area of concern.” The home range boundaries were
24        IDAHO WOOL GROWERS ASS’N V. VILSACK

developed using telemetry data from radio-collared bighorn
sheep. A second aspect of the model, the foray analysis, was
used to map the distances bighorn sheep travel outside their
home ranges. The Forest Service used the model, overall, to
predict whether a given foray by a bighorn from its core
home range would intersect a grazing allotment between May
and October, the months during which domestic sheep were
permitted to graze in the Payette. Contrary to Wool Growers’
argument, the risk of contact model does take into account
obstacles to mobility. The model incorporates telemetry data
of actual bighorn sheep movements within the Payette. That
data necessarily accounts for any topographical features that
impede bighorn mobility, as it indicates the distances bighorn
sheep actually move across the landscape.5 Also, bighorns’
chosen habitat is rugged, including steep, rocky terrain that
permits them to escape from predators. Thus, much of the
Payette’s mountainous terrain does not serve as a barrier to
bighorn sheep movement, although it might be a barrier to the
movement of other species. And the Forest Service has
pointed to evidence indicating that rivers are not obstacles to
bighorn sheep, as they have been known to swim across the
largest ones in the region. See W. Watersheds Project v.
BLM, No. 09-0507-E-BLW, 2009 WL 3335365, at *4 (D.
Idaho Oct. 14, 2009). Wool Growers’ argument that the risk
of contact model failed to account for barriers to movement
therefore fails.

  Wool Growers next contends that the risk of contact
model should have been validated by comparing the model’s


 5
   The FSEIS also notes that, for various reasons, the telemetry data does
not include some of the longest forays. It therefore underestimates the
distances moved by bighorn sheep and thus the extent to which they are
able to traverse challenging terrain. See FSEIS 3-35–36.
          IDAHO WOOL GROWERS ASS’N V. VILSACK                         25

predicted values with actual values to assess the model’s
reliability. Neither the Forest Service nor Intervenors directly
respond to this argument, although both generally note that
the models: (1) were developed by leading experts in the
field; (2) were derived from peer-reviewed and published
models used to study bighorn sheep movements in the Sierra
Nevada mountains of California; and (3) rely on a large data
set reflecting actual bighorn sheep movements in the Payette.6

    We reject Wool Growers’ argument. The Forest Service
is owed greater-than-average deference as it relates to its
choice of technical methodologies.             Also, as the
methodologies used to construct the risk of contact model
were peer-reviewed and used successfully elsewhere, it was
not unreasonable for the Forest Service to rely on the model,
adjusted to fit local circumstances in the Payette. The model
was reliable as a predictor of actual movements because it
was predicated on data depicting actual bighorn sheep
movements. Given the model’s Payette data-based origin, the
Forest Service could reasonably assume that its predictions
were sufficiently reliable to satisfy NEPA.

    Ultimately, the Forest Service used top-rate model
designers; relied on peer-reviewed methodologies applied by
other bighorn researchers addressing similar issues; and
incorporated on-the-ground data of bighorn sheep movements
within the Payette. Given the foregoing, and in light of the

 6
   Wool Growers also challenge the risk of contact model on the ground
that two of the Forest Service’s experts expressed conflicting views
regarding whether the model takes into account barriers to bighorn sheep
forays. Even assuming the experts’ statements conflict—and it is not clear
they do—those statements, which were presented only at the district court,
did not in any way affect the analysis in the FSEIS, which we find
reasonable.
26       IDAHO WOOL GROWERS ASS’N V. VILSACK

deference owed to the agency when undertaking technical
analysis within its purview, the Forest Service’s reliance on
the risk of contact model was not arbitrary, capricious, or an
abuse of discretion. Cf. Lands Council, 537 F.3d at 990–94
(holding that the Forest Service did not act arbitrarily and
capriciously by failing to verify its model with on-the-ground
data).

     2. Disease model

    Wool Growers asserts two final points of error, related to
the Forest Service’s disease model. Wool Growers contends
the model did not consider the effects of time on disease
transmission, including both when and for how long bighorn
and domestic sheep will be in contact with one another in the
Payette, as well as the precise timing and period of contact
necessary for transmission to occur.

    Determining both the amount of time bighorn and
domestic sheep spend cohabiting and the effects of timing on
disease transmission involve uncertainties acknowledged by
the Forest Service in the FSEIS. The degree to which both
kinds of uncertainty affect the usefulness of the disease model
can be resolved by the same three responses, as the Forest
Service explained in the FSEIS:

    (1) The disease model was not designed to predict actual
disease outbreak probabilities. Instead, the Forest Service
used the model to predict the likelihood that extirpation of
bighorn sheep subpopulations would result from various
alternative management plans, assuming probabilities of
disease transmission risk ranging from 5% to 100%. The
Forest Service did not use the disease model to predict a
particular level of actual risk.
         IDAHO WOOL GROWERS ASS’N V. VILSACK                    27

    (2) Because the steps of disease transmission are
uncertain—including the duration of contact between bighorn
and domestic sheep and the precise timing and coincidence of
events necessary for transmission to occur—the Forest
Service ran the model at multiple different probability values.
By using the model to test various proposed plans at different
risk levels, the Forest Service accounted for the uncertainty
of the variables involved.

     (3) Most importantly, the Forest Service clearly explained
the assumptions on which it built the model and the
uncertainties inherent in it, thereby identifying the model’s
limitations. The FSEIS states, for example: “We do not
understand all of the mechanisms involved in potential
disease transmission between the species,” FSEIS 3-13;
“[There is] so much uncertainty surrounding [the probability
of contact resulting in disease transmission] and essentially
no research . . . that would allow its estimation,” id. at 3-43;
and “[t]he complexity of the [disease transmission] model
and the number of variables whose estimation was necessary
to run it . . . imply a high degree of uncertainty of its results,”
id. at 3-56. Those explanations and acknowledgments are all
that NEPA requires. Powell, 395 F.3d at 1031–32 (citing 40
C.F.R. § 1500.1(b)). Were that not the case, government
actions affecting the environment, positively or negatively,
could be hamstrung by the need for unattainable scientific
certainty.

    Wool Growers points to additional available information
regarding domestic sheep movement within allotments—
grazing permits, operating instructions, and post-season
actual-use reports—the Forest Service could have used to
evaluate more accurately the likelihood that bighorn sheep
would cohabit with domestic sheep. But as the FSEIS
28        IDAHO WOOL GROWERS ASS’N V. VILSACK

explained, so much uncertainty surrounds contact
probabilities that the Forest Service chose not to estimate the
likelihood of actual contact. Specifically, the FSEIS observed
that, while this information was relevant, it could not be
incorporated into the modeling because domestic sheep: (1)
graze differently on the allotments each year; and (2) could be
anywhere in the Payette between May and October, and could
stray during that time or be left behind after the grazing
season. Given these uncertainties, the Forest Service did not
act unreasonably by using a range of probabilities to model
the risk of disease transmission.

    Wool Growers’ contention that the Forest Service should
have modeled a disease transmission probability of 0% fares
no better. If the disease transmission probability used was
0%, the models would necessarily show a 0% risk of
extirpation due to disease transmission for any possible
management plan. Because of the obviousness of this
outcome, a 0% value would not inform the environmental
review process. Perhaps the Forest Service could have used
a 1% probability to flesh out more fully the effects of disease
transmission, given various management alternatives. But in
the face of competing reasonable methodologies, we do not
substitute our judgment for that of the agency. That the
Forest Service could have chosen a different methodology
does not render the extensive analysis it undertook arbitrary
or capricious.7



     7
      The peer-reviewed Clifford study of bighorn sheep in the Sierra
Nevada assumed that, given contact between domestic and bighorn sheep,
the likelihood of disease transmission ranged from 50% to 100%. Here,
the Forest Service chose much more conservative probabilities for use in
its disease model.
         IDAHO WOOL GROWERS ASS’N V. VILSACK                    29

      In sum, the disease model was used for a limited purpose,
and, for that purpose, was sufficiently grounded in
scientifically acceptable methodology to shed some light on
the choice of an appropriate management plan. As the ROD
explained: “Determining the probability that a bighorn sheep
will reach an occupied [domestic sheep grazing] allotment [in
the Payette] and that contact between the species will result
in disease transmission is problematic,” partly because “there
is . . . essentially no research that would allow . . . estimation”
of the likelihood of disease transmission. ROD 12. Given
the Forest Service’s open acknowledgment of the model’s
limitations, the uncertainties inherent in estimating contact
and disease transmission, and the actual use of the
model—which was not to estimate actual probabilities of
disease transmission—the Forest Service’s development and
use of the disease model was not arbitrary, capricious, an
abuse of discretion, or otherwise contrary to law.

                               III.

   In light of the foregoing, we conclude that the Forest
Service committed no reversible error in preparing the FSEIS
and ROD. Accordingly, we AFFIRM.
