The western Burrowing Owl (Athene cunicularia hypugaea) has declined in many areas of its breeding range and is considered a species of national conservation concern in the United States and federally endangered in Canada. However, an overall evaluation of the species current status has not been possible due to lack of information on the abundance of Burrowing Owls in Mexico, where the species is widely distributed. In addition, observed declines in breeding populations in the United States and Canada may be related to factors on the wintering grounds in Mexico. This project is designed to address these issues. Researchers will estimate densities of Burrowing Owls in western Sonora during the breeding season of 2004 by surveying the irrigation districts of Guaymas, Costa de Hermosillo, Caborca, and Mexicali-San Luis Rio Colorado, using a standardized roadside point-count survey. They will also attempt to determine the ratio of migrant:resident Burrowing Owls in western Sonora during winter through stable isotope analyses of feathers.