## Facts

- The flat-tailed horned lizard inhabits desert areas in Arizona, California, and northern Mexico.
- In 1993, the U.S. Fish and Wildlife Service (FWS) proposed listing the lizard as threatened under the Endangered Species Act (ESA), citing habitat loss and fragmentation.
- In 1997, the Secretary withdrew the proposed listing, relying on a multijurisdictional Conservation Agreement and a view that the data did not show a clear population decline.
- Prior litigation resulted in remands requiring FWS to adequately analyze whether the species was endangered or threatened in a “significant portion of its range.”
- After the second remand, FWS again withdrew the proposed listing in 2006, acknowledging population data were limited and inconclusive but concluding the lost and threatened portion of the range was not “significant.”
- Conservation organizations and individual scientists sued under the ESA and the Administrative Procedure Act (APA), alleging the 2006 withdrawal was unlawful.
- The district court granted summary judgment to the Secretary; plaintiffs appealed.

## Issues

1. Whether the 2006 withdrawal of the proposed ESA listing was arbitrary and capricious under the APA because it failed to provide an adequate “significant portion of its range” analysis.
2. Whether the agency unlawfully treated limited, inconclusive, or ambiguous scientific information as affirmative support for declining to list the species.
3. Whether the agency adequately explained and supported its reliance on the Conservation Agreement and related management measures as reducing threats identified in the proposed listing.

## Decision

- The Ninth Circuit reversed the district court in part and remanded.
- The court held the Secretary’s 2006 withdrawal was arbitrary and capricious to the extent it relied on inconclusive science and an inadequately explained “significant portion of its range” determination.
- The court required the agency on remand to provide a reasoned explanation grounded in the record for (i) how it assessed significance of the threatened/lost range and (ii) how the evidence and conservation measures supported a no-listing decision.

## Legal Principles

- Under the APA, an agency must examine relevant data and articulate a rational connection between the facts found and the decision made; review is deferential but not a rubber stamp.
- ESA listing decisions must be based on the “best scientific and commercial data available” and must be accompanied by a satisfactory explanation showing how the record supports the outcome.
- The ESA requires analysis of whether a species is endangered or threatened “throughout all or a significant portion of its range”; an agency must meaningfully explain why a threatened or lost portion is or is not “significant.”
- Scientific uncertainty does not permit treating ambiguous or inconclusive studies as affirmative evidence that a species is secure; the agency must acknowledge limits and explain why the record still supports its conclusion.
- Reliance on conservation agreements and management measures is permissible only if the agency provides a reasoned, evidence-based explanation of their effectiveness and their relationship to the identified threats.

## Conclusion

The Ninth Circuit required a fuller, record-based explanation for declining to list the flat-tailed horned lizard, holding that the agency could not justify a no-listing decision by treating inconclusive science as proof of security and by offering only a cursory explanation for why threatened or lost habitat did not constitute a significant portion of the species’ range.


Tucson Herpetological Soc'y v. Salazar, 566 F.3d 870 (9th Cir. 2009)