## Facts

- The flat-tailed horned lizard inhabits the western Sonoran Desert and had been treated as an ESA candidate species since 1982 due to habitat loss and range reductions.
- In 1993, the U.S. Fish and Wildlife Service proposed listing the lizard as a threatened species under the Endangered Species Act (ESA).
- After litigation, a district court ordered the Secretary of the Interior to issue a final listing decision.
- In 1997, following adoption of a multi-agency Conservation Agreement aimed at protecting the lizard on certain public lands, the Secretary withdrew the proposed listing rule and declined to list the species.
- Conservation organizations and individuals challenged the withdrawal under the Administrative Procedure Act (APA), alleging the decision conflicted with the ESA and was arbitrary and capricious.
- The Secretary acknowledged threats and habitat loss on private lands but concluded sufficient habitat on public lands would ensure species survival.
- The Secretary construed the ESA phrase “throughout all or a significant portion of its range” to require listing only if the species faced extinction range-wide, or if endangerment in a portion implied extinction everywhere.

## Issues

1. Whether the Secretary’s interpretation of “in danger of extinction throughout all or a significant portion of its range” unlawfully rendered “significant portion of its range” without independent effect.
2. Whether the Secretary acted arbitrarily and capriciously by withdrawing the proposed rule without adequately evaluating whether the lizard was threatened in a significant portion of its range, including areas with severe habitat loss and fragmentation.
3. Whether the Secretary improperly relied on the Conservation Agreement without adequately assessing its likely implementation and effectiveness in reducing threats.

## Decision

- The Ninth Circuit reversed the district court’s summary judgment for the Secretary and remanded to the agency.
- The court held the Secretary’s statutory interpretation was erroneous because it made “significant portion of its range” redundant.
- The court held the nonlisting decision was arbitrary and capricious for applying an improper legal standard and for failing to address key aspects of the listing inquiry, including the significance of threatened portions of the range and the efficacy of the Conservation Agreement.

## Legal Principles

- Under the ESA, “significant portion of its range” must be given independent meaning; an agency may not interpret the phrase so that it adds nothing beyond range-wide extinction risk.
- ESA listing decisions must be based on the “best scientific and commercial data available” and must consider the statutory threat factors, including habitat destruction and the adequacy of existing regulatory mechanisms.
- Under APA review, an agency must consider relevant factors, examine the record, and provide a reasoned explanation connecting the facts found to the decision; failure to address important aspects of the problem is arbitrary and capricious.
- When an agency relies on a conservation plan to justify nonlisting, it must reasonably evaluate whether the plan is sufficiently certain to be implemented and effective to address the threats driving the listing proposal.

## Conclusion

The Ninth Circuit required the agency to reconsider the flat-tailed horned lizard’s listing status under a lawful construction of the ESA that treats endangerment in a significant portion of a species’ range as an independent basis for listing and to provide a reasoned, evidence-based explanation for its decision under the APA.


Defenders of Wildlife v. Norton, 258 F.3d 1136 (9th Cir. 2001)