National Association of Home Builders v. Norton

In 1992, the Fish and Wildlife Service (FWS) listed the Arizona pygmy-owl as endangered. The FWS designated the Arizona pygmy-owls as a discrete population segment (DPS) under the Endangered Species Act (ESA). The FWS found that pygmy-owl populations in the east and the west were discrete based on geographic isolation, distribution and status of habitat, and potential genetic distinctness. In the listing rule, the FWS subdivided the western pygmy-owls into an Arizona population and a northwestern Mexico population. The FWS found that the discrete population of Arizona pygmy-owls was significant to its taxon because if a loss of either of the subspecies of pygmy-owls were to occur, it would create a significant gap in the range of the remaining population. The FWS found in the listing rule that the Arizona pygmy-owls represented a small percentage of the pygmy-owls’ current range and did not find that their loss would significantly curtail the western pygmy-owls’ current range. The listing rule also found that a potential for genetic differences existed between the eastern and western pygmy-owls. The National Association of Home Builders (Home Builders) (plaintiffs) sued the FWS and sought to vacate the listing rule. The district court found that the FWS’s decision to divide the western pygmy-owl population at the border between Mexico and Arizona was permissible under the ESA. Home Builders appealed, arguing that the FWS violated the DPS Policy by designating the Arizona pygmy-owls as a DPS.