## Facts

- The Department of the Interior, through the U.S. Fish & Wildlife Service (FWS), implemented a gray wolf restoration program in the Northern Rockies under the Endangered Species Act (ESA).
- After earlier wolf extirpation in much of the region, the FWS adopted a recovery plan and later used ESA §10(j) to designate “nonessential experimental” populations for reintroduction into Yellowstone National Park and central Idaho.
- The final rules authorized reintroduction of up to approximately 150 wolves and defined the experimental populations to include both reintroduced wolves and any naturally dispersing wolves found within the designated geographic areas.
- The agencies acknowledged that individual wolves can disperse long distances and that some naturally dispersing wolves existed in or near the areas, but there were no reproducing wolf pairs in Yellowstone or central Idaho when the rules were adopted.
- Ranching and related groups challenged the rules, and the district court held the rules unlawful, reasoning that §10(j)’s requirement that experimental populations be “wholly separate geographically” barred any overlap with naturally occurring wolves.
- The district court also concluded the rules conflicted with the agency’s regulations by treating all wolves within the boundaries as experimental and amounted to an unlawful “de facto delisting” without following ESA §4 procedures; it ordered removal of reintroduced wolves (stayed pending appeal).

## Issues

1. Whether ESA §10(j)’s requirement that an experimental population be “wholly separate geographically” from nonexperimental populations is violated by the presence of individual naturally dispersing wolves within the experimental area.
2. Whether defining all wolves found within the experimental-population boundaries as “nonessential experimental” conflicts with the agency’s ESA regulations.
3. Whether the rules unlawfully reduce protections for naturally occurring wolves and therefore constitute a “de facto delisting” requiring ESA §4 procedures.
4. Whether, under the Administrative Procedure Act (APA), the rules reflect reasonable statutory and regulatory interpretations and are not arbitrary or capricious.

## Decision

- The Tenth Circuit reversed the district court and upheld the experimental-population rules.
- The court held that “wholly separate geographically” is properly read at the population level; sporadic presence of individual dispersers does not defeat §10(j) where no natural reproducing population exists in the area.
- The court concluded the Secretary permissibly defined the experimental populations and their geographic boundaries to include all wolves found within those boundaries, including dispersers.
- The court rejected the view that the rules effected a “de facto delisting,” holding that §10(j) expressly authorizes differentiated management for experimental populations.
- Applying APA review, the court found the agency’s interpretations reasonable and the rules “in accordance with law.”

## Legal Principles

- ESA §10(j)’s “wholly separate geographically” requirement concerns separation from nonexperimental *populations*, not the complete absence of individual animals that may disperse into the area.
- When statutory text is ambiguous, an agency’s reasonable interpretation adopted through rulemaking is entitled to deference under Chevron in APA review.
- An agency’s reasonable interpretation of its own implementing regulations receives substantial deference unless plainly erroneous or inconsistent with the regulation.
- Designating a “nonessential experimental” population under §10(j) and applying its management regime within the designated area does not constitute delisting under ESA §4 where the agency is acting within §10(j)’s authorization.

## Conclusion

The Tenth Circuit sustained the federal wolf reintroduction program’s §10(j) framework, holding that experimental populations may be geographically defined to include wolves within the area and that occasional dispersers do not invalidate the “wholly separate geographically” requirement absent an established natural reproducing population.


Wyoming Farm Bureau Fed’n v. Babbitt, 199 F.3d 1224 (10th Cir. 2000)