The plaintiffs, environmental groups and individuals, (Defenders) appealed a district court decision upholding a decision of the Secretary of the Interior (the Secretary) to withdraw a proposed rule to list the flat-tailed horned lizard as a threatened species under the Endangered Species Act (ESA).[1] The flat-tailed horned lizard, Phrynosoma mcallii, is a desert-dwelling species that inhabits areas of California, Arizona, and Mexico. In 1993 the Secretary published a proposed rule to protect the species under the ESA, about eleven years after the Secretary first identified it as a candidate for listing. Following a May 1997 district court order compelling the Secretary to decide the lizard's status, on July 15, 1997 the Secretary issued her decision not to designate the lizard as a threatened species. Defenders challenged the decision in district court. The district court granted summary judgment for the Secretary, holding that the Secretary reasonably relied on a conservation agreement signed by a group of federal and state agencies to decide that none of the statutory factors that would require the listing of the lizard were present.[2] On appeal, the Ninth Circuit reversed the district court's ruling, holding that the Secretary's decision to withdraw the rule was arbitrary and capricious.

The ESA provides five factors upon which the Secretary should base her decision to designate a species as threatened.[3] Defenders argued that up to four of these five factors were present. The Secretary countered that even if the species faced significant threats on private lands, public land would provide significant habitat for the species, and that measures undertaken on public land would protect the species adequately. In particular, the Secretary indicated that a recent conservation agreement, signed by a group of federal and state agencies, would reduce threats to the lizard. The conservation agreement created a management strategy for the lizard that included the designation of five "management areas" in which specific actions, such as population monitoring, would be undertaken to protect the lizard.

In analyzing these arguments, the Ninth Circuit focused on the meaning of the statutory phrase "in danger of extinction throughout . . . a significant portion of its range."[4] The ESA defines a species as endangered if it "is in danger of extinction throughout all or a significant portion of its range."[5] A threatened species is one that "is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range."[6] The Secretary's final decision withdrawing the proposed rule did not consider whether the lizard was extinct, endangered, or likely to become endangered in "a significant portion of its range."[7] Instead, based upon her interpretation of the phrase "extinction throughout . . . a significant portion of its range,"[8] the Secretary argued on appeal, that a species is threatened only if the entire species is threatened, either because the species is currently threatened over all of its range or because the portions of its range in which the species is extinct, endangered, or threatened are significant enough that the entire species is likely to become threatened. Therefore, because of the large amount of available public land, the danger to the lizard on private land was not significant enough to threaten the entire species.

The court disagreed with the Secretary's interpretation of the phrase. The court stated that the Secretary's explanation would render the statute redundant because a species threatened over "a significant portion of its range" would also be a species threatened "throughout all . . . of its range."[9] The court explained that it must "follow a 'natural reading . . ., which would give effect to all of [the statute's] provisions.'"[10] Therefore, the court could not interpret the term "all" and the phrase "a significant portion" to mean the same thing. The Secretary also argued that Congress included the "significant portion of its range" language in an attempt to conserve species at an early stage, before facing endangerment throughout its entire range. The court disagreed, stating that Congress addressed the need to conserve a species early--before it becomes close to extinction--by creating the "threatened" designation in addition to the "endangered" designation.

However, the court also did not agree with Defenders' interpretation of the phrase. Defenders used a quantitative approach, arguing that the lizard is threatened in "a substantial portion of its range" because it is projected to lose eighty-two percent of its habitat.[11] Defenders argued that because other courts had held that smaller losses of habitat were sufficient to necessitate listing of other species, the lizard also should be listed. The Ninth Circuit disagreed because (1) the argument suggested a species necessarily would be threatened or endangered simply because a certain percentage of the species range was lost, and (2) had Congress intended to use quantitative criteria to determine when to designate a species as endangered or threatened, it would have included the criteria in the statute.

The Ninth Circuit turned to legislative history to determine what Congress intended the phrase "extinction throughout . . .a significant portion of its range" to mean.[12] The court explained that Congress used this language to expand the definition of "endangered" that had been used in previous endangered species acts. Congress intended to provide a means by which the Secretary can designate a species as endangered or threatened in one portion of its range while using a different designation, or declining to the list the species at all, in another portion of its range. Based upon this interpretation of the phrase, the court determined that when the Secretary determined that the lizard should not be listed as threatened she overlooked a crucial consideration: whether the lizard's range on private lands is a "significant portion of its range" and if so, whether the lizard is therefore in danger of "extinction throughout . . . a significant portion of its range."[13] The Secretary also failed to consider whether the lizard might be threatened in one state or subportion of a state, but not in another state.

In addition, the court criticized the Secretary's reliance on the conservation agreement. The court stated that the Secretary failed to address how each management area would benefit the species, especially considering that implementation of some of the management areas had been delayed. The Secretary's explanation of the conservation agreement's benefits was not adequate to address the possibility that the lizard might be threatened throughout "a significant portion of its range."[14]

Based upon the Secretary's inadequate explanation of the benefits of the conservation agreement and the Secretary's failure to address whether the lizard was threatened throughout "a significant portion of its range,"[15] the Ninth Circuit held that the Secretary's decision to withdraw the proposed rule to list the lizard as threatened was arbitrary and capricious. The Ninth Circuit reversed the district court and remanded to the Secretary for reconsideration.