                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

KERN COUNTY FARM BUREAU; KERN           
COUNTY WATER AGENCY; NORTH
KERN COUNTY WATER STORAGE
DISTRICT; COALITION OF PRIVATE
PROPERTY RIGHTS; ROSEDALE-RIO
BRAVO WATER STORAGE DISTRICT;
SEMITROPIC WATER STORAGE
DISTRICT; WHEELER RIDGE
MARICOPA WATER STORAGE
DISTRICT; COUNTY OF KERN,
               Plaintiffs-Appellants,
                  v.                          No. 04-15540
DAVE ALLEN, Regional Director of
the U.S. Fish and Wildlife Service,            D.C. No.
                                            CV-02-05376-AWI
Region 1; STEVEN A. WILLIAMS,                  OPINION
Director of the U.S. Fish and
Wildlife Service; GALE A. NORTON,
Secretary of the Interior; UNITED
STATES DEPARTMENT OF THE
INTERIOR; U.S. FISH AND WILDLIFE
SERVICE,
              Defendants-Appellees,
                 and
CENTER FOR BIOLOGICAL DIVERSITY,
              Intervenor-Defendant-
                           Appellee.
                                        
        Appeal from the United States District Court
           for the Eastern District of California
        Anthony W. Ishii, District Judge, Presiding


                             6855
6856        KERN COUNTY FARM BUREAU v. ALLEN
                  Argued and Submitted
       February 16, 2006—San Francisco, California

                   Filed June 20, 2006

  Before: J. Clifford Wallace, Michael Daly Hawkins, and
             Sidney R. Thomas, Circuit Judges.

               Opinion by Judge Hawkins
6858        KERN COUNTY FARM BUREAU v. ALLEN


                       COUNSEL

Robert D. Thornton, Nossaman, Guthner, Knox & Elliott,
Irvine, California, for the plaintiffs-appellants.

Matthew J. Sanders, U.S. Department of Justice, Environmen-
tal & Natural Resources Division, Washington, D.C., for the
defendants-appellees.

Matt Kenna, Kenna & Hickcox, Durango, Colorado, for the
intervenor-defendant-appellee.

M. Reed Hopper, Pacific Legal Foundation, Sacramento, Cal-
ifornia, for amicus curiae Pacific Legal Foundation.
              KERN COUNTY FARM BUREAU v. ALLEN               6859
                           OPINION

HAWKINS, Circuit Judge:

   Kern County Farm Bureau, et al. (“Kern”), appeal from the
district court’s judgment denying their claim against the U.S.
Fish & Wildlife Service (“FWS”) for listing the Buena Vista
Lake shrew (“the BVL shrew”) as an endangered species,
contending that FWS violated the Endangered Species Act
(“ESA”) and the Administrative Procedure Act (“APA”) by
failing to provide public review and comment on new studies
that became available after the close of the comment period,
not basing its listing decision on the best scientific data avail-
able, not summarizing the data underlying its decision, and
not showing the relationship between the data and its deci-
sion. Because the post-comment information was only impor-
tant, not critical, to FWS’s decision, and given the deference
owed to agencies in making such scientifically-based deci-
sions, we affirm the district court’s judgment.

                     I.   Factual History

  The BVL shrew is a subspecies of ornate shrews endemic
to Kern County, California. 67 Fed. Reg. 10101 (Mar. 6,
2002) (codified at 5 C.F.R. pt. 17). Fewer than thirty are
known to exist. Id. at 10110.

   On June 1, 2000, FWS published a rule proposing to list the
BVL shrew as an endangered subspecies under the ESA. 65
Fed. Reg. 35033 (June 1, 2000). The proposal explained that
only thirty-eight BVL shrews had been observed since their
rediscovery in 1986, and that the only known population
existed in a small wetland area on private property. Id. at
35033-34. The proposal emphasized that the amount of suit-
able habitat for the BVL shrew had been significantly reduced
while noting that additional patches of habitable land in the
area that might have supported the BVL shrew were “mar-
ginal at best and would not likely [have] support[ed] a signifi-
6860           KERN COUNTY FARM BUREAU v. ALLEN
cant number of animals.” Id. at 35036 (citation omitted). The
Proposed Rule explained that this “loss and fragmentation of
habitat due to human activities” was “[t]he primary cause of
decline of the [BVL] shrew.” Id. Additionally, FWS found
that the BVL shrew was threatened “by agricultural activities,
modifications and potential impacts to local hydrology, uncer-
tainty of water delivery . . . , possible toxic effects from sele-
nium poisoning, and by random naturally occurring events.”
Id. at 35038. FWS concluded that there was a high probability
that these threats would have “result[ed] in the extinction of
the [BVL] shrew . . . .” Id.

   FWS opened a sixty-day comment period for the proposal,
seeking information about threats to the BVL shrew, locations
of any additional populations, and “the range, distribution,
and population size and genetics of this subspecies.” Id. at
35039. FWS then reopened the comment period for another
sixty days “to provide all interested parties additional oppor-
tunity to . . . [comment] on the proposal.” 65 Fed. Reg. 49530
(Aug. 14, 2000). Further, FWS “solicited the expert opinions
of five independent specialists regarding the biological and
ecological information about the [BVL] shrew contained in
the proposed rule.” 67 Fed. Reg. at 10105. Of the four peer
reviewers who responded within the comment period, three
“stated that the proposed rule was an accurate summary of the
species biology and status,” while one “felt that additional
surveys and improved management of known populations . . .
could eliminate the need to list the species.” Id. at 10106.
Ultimately, three supported the listing, while the fourth
remained neutral.1

  After the comment period, but before issuance of the Final
Rule, three new studies became available. Two of the studies
dealt with morphological and genetic variations among the
multiple subdivisions of ornate shrews, while the third
  1
   The fifth peer reviewer, Daniel Williams, responded one year after the
open comment period and recommended postponing the listing.
               KERN COUNTY FARM BUREAU v. ALLEN                   6861
assessed the distribution, habitat, and status of the BVL
shrew. See infra Section IV.A. Following the release of these
new studies, FWS did not reopen the public comment period.
Instead, on March 6, 2002, it published the Final Rule listing
the BVL shrew as an endangered subspecies. 67 Fed. Reg. at
10101. The Final Rule responded to various comments on the
Proposed Rule and incorporated some of the data from the
new studies. Nevertheless, it listed factors nearly identical to
those mentioned in the Proposed Rule to justify its listing
decision and concluded that listing the BVL shrew as endan-
gered was “the preferred action.” 67 Fed. Reg. at 10110.

  Kern soon thereafter filed its complaint, primarily alleging
various APA and ESA violations. After a bench trial, judg-
ment was entered in favor of FWS, and Kern filed this appeal.

                   II.   Statutory Framework

   The APA requires federal agencies to publish a general
notice of proposed rule making in the Federal Register to
“give interested persons an opportunity to participate in the
rule making through submission of written data, views, or
arguments with or without opportunity for oral presentation,”
and “[a]fter consideration of the relevant matter presented, . . .
[to] incorporate in the rules adopted a concise general state-
ment of their basis and purpose.” 5 U.S.C. § 553(b)-(c); see
also 16 U.S.C. § 1533(b)(4) (ESA listing decisions must com-
ply with the APA, 5 U.S.C. § 553).

   Under the ESA, an endangered species is “any species
which is in danger of extinction throughout all or a significant
portion of its range . . . .” 16 U.S.C. § 1532(6).2 A “species”
includes “any subspecies of . . . wildlife . . . and any distinct
population segment of any species of . . . wildlife which inter-
breeds when mature.” 16 U.S.C. § 1532(16). The decision to
  2
   FWS is one of the agencies responsible for administering the ESA. See
50 C.F.R. § 402.01(b) (1986).
6862         KERN COUNTY FARM BUREAU v. ALLEN
list a species as endangered is based on five statutorily pre-
scribed factors, any one of which may support a listing deter-
mination: (1) “the present or threatened destruction,
modification, or curtailment of its habitat or range;” (2) “over-
utilization for commercial, recreational, scientific, or educa-
tional purposes;” (3) “disease or predation;” (4) “the
inadequacy of existing regulatory mechanisms;” or (5) “other
natural or manmade factors affecting its continued existence.”
16 U.S.C. § 1533(a)(1)(A)-(E).

   Listing determinations must be made “solely on the basis
of the best scientific and commercial data available . . . .” 16
U.S.C. § 1533(b)(1)(A). Additionally, FWS must include in
any proposed or final listing decision “a summary . . . of the
data on which such regulation is based and [must] show the
relationship of such data to such regulation . . . .” 16 U.S.C.
§ 1533(b)(8).

                  III.   Standard of Review

   The APA provides that final agency action shall be set
aside if it is “arbitrary, capricious, an abuse of discretion, or
otherwise not in accordance with the law,” or if it is taken
“without observance of procedure required by law.” 5 U.S.C.
§ 706(2)(A), (D); accord Idaho Farm Bureau Fed’n v. Bab-
bitt, 58 F.3d 1392, 1401 (9th Cir. 1995). The arbitrary and
capricious standard is “highly deferential, presuming the
agency action to be valid and [requires] affirming the agency
action if a reasonable basis exists for its decision.” Indep.
Acceptance Co. v. California, 204 F.3d 1247, 1251 (9th Cir.
2000) (quotations and citations omitted). Under such deferen-
tial review, we may not substitute our judgment for that of the
agency. Marsh v. Or. Natural Res. Council, 490 U.S. 360, 376
(1989).

  Unlike substantive challenges, however, our review of an
agency’s procedural compliance is exacting, yet limited. See
Coalition For Gov’t Procurement v. Fed. Prison Indus., Inc.,
             KERN COUNTY FARM BUREAU v. ALLEN                 6863
365 F.3d 435, 457 (6th Cir. 2004) (citing Natural Res. Def.
Council, Inc. v. SEC, 606 F.2d 1031, 1045, 1048-49 (D.C.
Cir. 1979)); Campanale & Sons, Inc. v. Evans, 311 F.3d 109,
116 (1st Cir. 2002). We review de novo but are limited to
ensuring that “ ‘statutorily prescribed procedures have been
followed.’ ” Campanale & Sons, 311 F.3d at 116 (quoting
Natural Res. Def. Council, Inc., 606 F.2d at 1045). Further,
we determine “the adequacy of the agency’s notice and com-
ment procedure, without deferring to an agency’s own opin-
ion of the . . . opportunities it provided.” Natural Res. Def.
Council v. EPA, 279 F.3d 1180, 1186 (9th Cir. 2002).

                       IV.   Discussion

A.   Notice and Comment for New Studies

   [1] Integral to an agency’s notice requirement is its duty to
“identify and make available technical studies and data that it
has employed in reaching the decisions to propose particular
rules. An agency commits serious procedural error when it
fails to reveal portions of the technical basis for a proposed
rule in time to allow for meaningful commentary.” Solite
Corp. v. EPA, 952 F.2d 473, 484 (D.C. Cir. 1991) (quotations,
punctuation, and citation omitted). Yet, “[n]othing prohibits
[an a]gency from adding supporting documentation for a final
rule in response to public comments.” Rybachek v. EPA, 904
F.2d 1276, 1286 (9th Cir. 1990). After publishing a proposed
rule, agencies often receive new information, which in turn
improves the accuracy of agency action:

     It is perfectly predictable that new data will come in
     during the comment period, either submitted by the
     public with comments or collected by the agency in
     a continuing effort to give the regulations a more
     accurate foundation. The agency should be encour-
     aged to use such information in its final calculations
     without thereby risking the requirement of a new
     comment period.
6864           KERN COUNTY FARM BUREAU v. ALLEN
BASF Wyandotte Corp. v. Costle, 598 F.2d 637, 644-45 (1st
Cir. 1979).

   [2] Accordingly, the public is not entitled to review and
comment on every piece of information utilized during rule
making. Instead, an agency, without reopening the comment
period, may use “supplementary data, unavailable during the
notice and comment period, that expands on and confirms
information contained in the proposed rulemaking and
addresses alleged deficiencies in the pre-existing data, so long
as no prejudice is shown.” Idaho Farm Bureau Fed’n, 58 F.3d
at 1402 (quoting Solite Corp., 952 F.2d at 484) (internal quo-
tations omitted).

   In Idaho Farm Bureau Federation, we held that FWS com-
mitted procedural error in listing the Bruneau Hot Springs
Snail as an endangered species because it failed to provide the
public with an opportunity to review and comment on new
material in the record. 58 F.3d at 1404. The new material “did
not merely supplement or confirm existing data,” but rather
“provided the only scientific information on the cause of the
decline in [the Snail’s habitat,]” and, therefore, constituted
“unique information that was not duplicated in other reports.”
Id. at 1402-03. The need for notice and comment was “greatly
heightened because FWS relied largely on the [new] study to
support its final rule.” Id. at 1403. In particular, the study
“was critical to FWS’[s listing] decision,” because “FWS sup-
port[ed] its key analysis by citing the [new] study.” Id. at
1403; see also Ober v. EPA, 84 F.3d 304, 314-15 (9th Cir.
1996) (reopening the public comment period because the
additional materials were relied on and “critical” to the agen-
cy’s decision). Additionally, the need for public comment was
exacerbated by the questionable accuracy of the new study.3
We noted that in Idaho Farm Bureau Fed’n, 58 F.3d at 1403,
  3
    The report was a provisional draft that the FWS did not want released
to the public and was discovered to have had several errors. Idaho Farm
Bureau Fed’n, 58 F.3d at 1403.
               KERN COUNTY FARM BUREAU v. ALLEN                   6865
the “[o]pportunity for public comment is particularly crucial
when the accuracy of important material in the record is in
question.”

   In contrast, the D.C. Circuit, in Solite Corp., upheld the
EPA’s failure to provide a public opportunity to comment on
new data used in the Final Rule. 952 F.2d at 484-85. The EPA
had “replaced one report with a later report as the source of
data on which final quantitative measurements were based.”
Idaho Farm Bureau Fed’n, 58 F.3d at 1402 (explaining Solite
Corp., 952 F.2d at 484). In affirming the EPA’s actions, the
court found it significant that the accuracy of the new data
was not challenged, that the record did not suggest that the
agency hid the information or conducted rule making in bad
faith, that the new data confirmed prior assessments, and that
the agency’s methodology remained constant. Solite Corp.,
952 F.2d at 484-85.

   Here, the first post-comment study was a range-wide
genetic study of 251 shrew specimens by Dr. Jesus Mal-
donado. Jesus E. Maldonado, et al., Tripartite genetic subdivi-
sions in the ornate shrew (Sorex ornatus), 10 MOLECULAR
ECOLOGY 127 (2001) [hereinafter 2001 Maldonado Study].
This study evaluated genetic variations among ornate shrews
at twenty localities and postulated that ornate shrews in Cali-
fornia could be organized into three “clades” — northern,
central (to which the BVL shrew belongs), and southern.4 Id.
The study noted that “[t]he ornate shrew is one of the most
threatened small mammals” in California, “primarily due to
destruction of wetlands and riparian habitats . . . .” Id. at 143.
The study did not purport to change the taxonomic classifica-
tion of the BVL shrew, referring to it as a separate subspecies.
Id.
  4
    A clade is a “group of organisms, such as a species, whose members
share homologous features derived from a common ancestor.” American
Heritage Dictionary of the English Language (4th ed. 2000), available at
http://www.bartleby.com/reference.
6866           KERN COUNTY FARM BUREAU v. ALLEN
   A second post-comment study, also conducted by Dr. Mal-
donado,5 examined the morphological characteristics of over
500 ornate shrew skulls throughout the species’ range to
determine if any differences existed, and, if so, whether they
corresponded to the three genetic clades identified in his 2001
study. See Jesus E. Maldonado, Discordant Patterns of Mor-
phological Variation in Genetically Divergent Populations of
Ornate Shrews (Sorex Ornatus) (forthcoming 2004) [hereinaf-
ter Morphological Study]. Maldonado found “significant mor-
phological differences between ornate shrew populations,”
which did not correspond to the three genetic clades he had
previously identified. Id. at 12. Further, the morphological
differences between subspecies “seem[ed] to portray the pat-
terns of variation [between shrew populations] better than the
genetic regions” identified in the 2001 Maldonado Study. Id.
He concluded that the “current boundaries for the seven sub-
species that were analyzed in [the] study[ ] correspond[ed] to
morphological divergence and should therefore continue to be
considered [Evolutionarily Significant Units].”6 Id. at 13.

   The third post-comment study, authored by Daniel Wil-
liams and Adam Harpster, assessed “the distribution, habitat
association, and population status of the [BVL] shrew” by
trapping for shrews at six sites.7 See Daniel Williams & Adam
Harpster, Status of the Buena Vista Lake Shrew (Sorex Orna-
tus Relictus) (Oct. 29, 2001) (unpublished report, on file with
the U.S. Bureau of Reclamation) [hereinafter Status Review].
The trapping caught sixteen shrews at three of the six sites. Id.
   5
     This study was unpublished during the rule making process, but was
later published. Discordant Patterns of Morphological Variation in Genet-
ically Divergent Populations of Ornate Shrews (Sorex Ornatus), 85 J. OF
MAMMOLOGY 886 (2004).
   6
     An Evolutionarily Significant Unit is “a set of populations that has
been historically isolated and, accordingly, is likely to have a distinct
potential.” Id. at 13 (quotations and citation omitted).
   7
     The study was commissioned by the Central Valley Project Improve-
ment Act and administered, in part, by FWS.
              KERN COUNTY FARM BUREAU v. ALLEN               6867
at 9. These three additional BVL shrew populations were dis-
covered in wetland and riparian habitat that had been reduced
to “10 small, degraded, and scattered remnants . . . .” Id. at
10. The Status Review speculated “that ornate shrews may
reside on actively farmed ground, or . . . cultivated fields,” but
limited its hypothesis to ornate shrews generally (not BVL
shrews), and based its belief on a survey of “unknown signifi-
cance.” Id. at 13-14. Further, it surmised that BVL shrews
“also rarely will be found in more arid, upland communities,”
but noted that such communities “are extremely reduced and
isolated in small parcels,” and “might provide extremely low
quality habitat for [BVL] shrews . . . .” Id. at 13.

   Although the study deduced that “measures to conserve and
enhance [BVL shrew] populations are justified,” and cau-
tioned that it “[did] not have insight into the size and extent
of [BVL shrew] populations,” the authors did “not believe
that [BVL] shrews are endangered now, nor are there foresee-
able threats to remaining populations in the near future.” Id.
at 16. It reached this conclusion, in part, by noting that several
possible initiatives in the region “hold great promise for
greatly enhancing populations of [BVL] shrews.” Id. Still, the
study found that “the long-term persistence of [BVL] shrews
depends upon maintenance of riparian and wetland communi-
ties in the southern Tulare Basin . . . and enhancing the size
and connectivity between the small and mostly isolated habi-
tats where the shrews currently are found.” Id.

   Like the petitioners in Solite Corp., Kern does not point to
inaccuracies in the new studies. Id. at 484. Nor does the
record suggest that FWS hid the information from the public
or conducted rule making in bad faith. Rather, Kern contends
that the new studies were critical to the listing decision.

   The district court correctly concluded that the new studies
merely supplemented the data in the Proposed Rule. Unlike
the post-comment study in Idaho Farm Bureau Federation,
the new materials do not provide the sole, essential support
6868          KERN COUNTY FARM BUREAU v. ALLEN
for the listing decision. Instead, as in Solite Corp., the studies
confirm and expand on existing data, providing additional
grounds for the well-supported conclusions in the Proposed
Rule. Id. at 485. Moreover, the new studies did not alter the
justifications or conclusions that were vital to the listing deci-
sion. Just like the Proposed Rule, FWS concluded in the Final
Rule that the BVL shrew was a distinct subspecies threatened
with extinction, explaining that few BVL shrews remain, that
the amount of suitable habitat has been significantly reduced,
and that several factors jeopardize the BVL shrew’s continued
existence. Indeed, the entire discussion of the extinction fac-
tors in the Final Rule strongly resembles the factors provided
in the Proposed Rule. Compare 67 Fed. Reg. at 10106-10 with
65 Fed. Reg. at 35036-38.

  Despite the limited use of the new studies and the analytical
symmetry between the two rules, Kern argues that further
notice and comment was required, basing its claim on three
assertions: (1) the new studies provided crucial information
on whether the BVL shrew is a distinct subspecies; (2) the
new studies provided crucial information on whether the BVL
shrew is in danger of extinction; and (3) the new studies
undermined the listing decision.

  1.   Subspecies Distinction

   [3] To be eligible for an endangered species listing, an ani-
mal must first be classified, at a minimum, as a distinct sub-
species. See 16 U.S.C. § 1532(16). FWS used the 2001
Maldonado Study and the Morphological Study in the Final
Rule only to describe further the distinct morphological and
genetic characteristics of the BVL shrew subspecies. 67 Fed.
Reg. at 10101. FWS sought to “add depth” to its morphologi-
cal discussion by incorporating these studies into the Final
Rule. The Proposed Rule primarily supported the conven-
tional conclusion that the BVL shrew is a distinct subspecies
by citing to a 1932 study by Dr. Grinnell, which, according
to FWS, is the only scientifically valid, peer-reviewed, and
                KERN COUNTY FARM BUREAU v. ALLEN                      6869
published taxonomic treatment of the BVL shrew. 65 Fed.
Reg. at 35033-34. The Maldonado studies confirmed FWS’s
previous conclusion by providing additional data on the BVL
shrew’s morphological and genetic characteristics. Having
reached an identical conclusion that affirmed its already-
supported subspecies classification, FWS’s use of the Mal-
donado studies in the Final Rule was far from critical to its
listing decision.

  2.    Danger of Extinction

   [4] Upon concluding that the BVL shrew was a distinct
subspecies, FWS sought to determine whether the shrew was
“in danger of extinction throughout all or a significant portion
of its range . . . .” 16 U.S.C. § 1532(6). FWS found that few
BVL shrews remained and determined that several factors
subjected the BVL shrew to a substantial risk of extinction
throughout its range. The Final Rule used the Status Review
to expand on its discussion of the BVL shrew’s population
and range, integrating the Status Review’s data with all that
was known and cited in the Proposed Rule. Some of the revi-
sions provided by the Status Review were unquestionably sig-
nificant. In discovering three new populations of BVL shrews,
the Status Review nearly doubled the number of known
shrews to thirty. Further, the Status Review provided more
detailed information on the current range of the BVL shrew
and on the suitability of various habitats. None of the new
information, however, adversely affected FWS’s underlying
reasons for its conclusion.8 The Status Review’s data simply
supplemented the existing data, confirming that few BVL
shrews existed and that their most suitable habitat remained
fragmented, degraded, and scattered. Status Review at 10-12.
Because the Status Review provided useful data that supple-
mented FWS’s existing understanding of the BVL shew, but
  8
    One FWS official found that the Status Review “ma[de] a stronger case
for listing than delisting,” while another determined that the data from the
Status Review “d[id] not change the conclusion for the final rule.”
6870         KERN COUNTY FARM BUREAU v. ALLEN
did not alter the primary conclusions from the Proposed Rule,
it was not critical to FWS’s decision.

  3.   Listing Decision Validity

   Kern’s primary objection to FWS’s use of the Status
Review essentially emanates from the Status Review’s oppos-
ing conclusion that the BVL shrew should not be listed as
endangered. Despite the conflicting opinion, FWS concluded
that the data from the Status Review was consistent with its
listing decision. Kern’s concern is misplaced because FWS is
not required to accept the Status Review’s conclusion, but
rather simply must use the Status Review’s data in reaching its
listing decision. See infra Section IV.B; 16 U.S.C.
§ 1533(b)(1)(A). To the extent that Kern disputes FWS’s
interpretation of the data in the new studies or seeks an evalu-
ation of FWS’s data and conclusion, its claim constitutes a
substantive challenge to the listing decision.

   In fact, much of Kern’s argument appears to be a substan-
tive claim couched in alleged procedural violations. Kern’s
principal contention is less concerned with the degree to
which the Final Rule relies on the new studies than it is on the
extent to which the new studies undercut the Final Rule. Kern
initially presents a procedural argument that the new studies
were critical to the listing decision and thus require public
comment, but then spends most of its analysis attempting to
demonstrate how the three studies actually undermine the key
premises in FWS’s listing decision (a substantive issue merit-
ing the more stringent arbitrary and capricious review).
Kern’s procedural claims thus appear inextricably intertwined
with its substantive contention that FWS misinterpreted the
information from the new studies. Because Kern emphasizes
that it only raises procedural violations in this appeal, how-
ever, such substantive issues are not properly before us.

  4.   Conclusion

  [5] Ultimately, the new studies were not vital to FWS’s
decision as they were not used to introduce a new premise, to
             KERN COUNTY FARM BUREAU v. ALLEN               6871
justify independently the final decision, or to reach a different
conclusion. Instead, the Final Rule discusses virtually identi-
cal factors as those in the Proposed Rule in deciding to list the
BVL shrew. Having used the new studies merely to refine and
expand on its pre-existing data, FWS was not required to
reopen the public comment period.

B.   Best Scientific Data Available

   [6] Kern argues that FWS failed to utilize the data from the
three studies in reaching its listing decision and, therefore,
violated the ESA’s requirement to base its determination on
the “best scientific and commercial data available.” 16 U.S.C.
§ 1533(b)(1)(A ). The best available data requirement “merely
prohibits [an agency] from disregarding available scientific
evidence that is in some way better than the evidence [it]
relies on.” Southwest Ctr. for Biological Diversity v. Babbitt,
215 F.3d 58, 60 (D.C. Cir. 2000) (quotations omitted). Essen-
tially, FWS “cannot ignore available biological information.”
Conner v. Burford, 848 F.2d 1441, 1454 (9th Cir. 1988).

   [7] Because Kern “point[s] to no data that was omitted
from consideration,” Building Indus. Ass’n of Superior Cali-
fornia v. Norton, 247 F.3d 1241, 1246 (D.C. Cir. 2001) (quo-
tations omitted), this second claim also fails. “[A]bsent
superior data . . . occasional imperfections do not violate
§ 1533(b)(1)(A).” Id. at 1247. Kern does not allege that FWS
actually omitted the three new studies from the Final Rule.
The Final Rule contains at least twenty citations to the three
new studies. Instead, Kern’s claim is hitched to its assertion
that FWS misinterpreted the new studies. See supra Section
IV.A.3. Kern essentially contends that all three studies under-
mine the Final Rule and, therefore, FWS “in reality ignored
them.”

   [8] The record, however, is replete with examples to the
contrary. FWS thoroughly evaluated and incorporated the data
from all three studies in making its listing decision. The data
6872          KERN COUNTY FARM BUREAU v. ALLEN
from the studies are discussed and evaluated throughout the
Final Rule, and e-mail traffic from agency officials demon-
strates that FWS examined the data from the new studies in
promulgating the Final Rule. Without any evidence in the
record that FWS ignored relevant information, we hold that
FWS satisfied its duty to base its listing determinations on the
best available data.

C.     Relationship of Data to Listing Decision

   Finally, Kern contends that FWS failed to summarize the
data underlying the Final Rule and to show the relationship of
the data to the Final Rule, as required by 16 U.S.C.
§ 1533(b)(8). Kern supports its claim by listing various ques-
tions that it claims were left unanswered by FWS. We reject
Kern’s attempt to mandate that FWS answer its particular
questions before making a listing decision. FWS’s discussion
of the data and analysis of the extinction factors adequately
satisfied its ESA requirements.

    The Final Rule is extensively documented (citing over 100
sources) and contains abundant data and explanations sup-
porting FWS’s ultimate decision. It comprehensively
describes the existing data on the BVL shrew, noting that
“there are less than 30 known individuals in four populations
. . . .” 67 Fed. Reg. at 10110. Such scarce numbers make the
BVL shrew “extremely vulnerable” to environmental impacts
and risks associated with small, restricted populations. Id.
These risks, which can lead to extinction, include “the loss or
alteration of essential elements for breeding, feeding, and
sheltering; the introduction of limiting factors into the envi-
ronment such as poison or predators; and catastrophic random
changes or environmental perturbations, such as floods,
droughts, or disease.” Id. (citation omitted).

  The Final Rule goes on to examine particular threats to the
BVL shrew’s continued existence, finding that (1) the
“amount of suitable habitat for the [BVL] shrew has been sig-
              KERN COUNTY FARM BUREAU v. ALLEN                6873
nificantly reduced over time,” resulting in the elimination of
“over 95 percent of the riparian vegetation and associated
marsh habitat” that could serve as suitable habitat for the BVL
shrew, id. at 10106, (2) the water supply is unable to support
ecosystem function throughout the BVL shrew’s entire habi-
tat, id., (3) “[t]he small population size and restricted distribu-
tion [of BVL shrews] increases their vulnerability to epidemic
diseases” and deleterious genes through inbreeding, id. at
10107, (4) existing regulatory mechanisms “have not been
adequate in preventing the destruction of the limited [BVL]
shrew habitat,” id. at 10106-10, and (5) “[s]elenium toxicity
represents a serious threat to the continued existence and
recovery of the [BVL] shrew,” id. at 10107-08. Given the
“high potential that these threats could result in the extinction
of the [BVL] shrew,” the Final Rule concludes that “the pre-
ferred action is to list the [BVL] shrew as endangered.” Id. at
10110. Nothing more was required of FWS and, therefore,
Kern’s third claim is also without merit.

                        V.   Conclusion

  [9] For the foregoing reasons, FWS adequately complied
with its APA and ESA procedural requirements. Accordingly,
we affirm the district court’s determination that no serious or
substantial reason exists to negate the listing and provide for
a new comment period.

  AFFIRMED.
