“Indicator” species of natural habitat quality are potentially useful tools for managers of biodiversity (Rohlf 1991). Predators are often considered indicators because they are at the top of food webs and need wide home-range areas to function. Predators play an important role in ecosystems because they can determine the community structure patterns of their prey (Menge et al. 1994). In addition, predators, including facultative scavengers, have been used as “umbrella” species in world conservation strategies because their protection may facilitate the conservation of great portions of unaltered habitats (Simberloff 1987). Raptors, here defined to include New World vultures, Falconiformes, and Strigiformes, have been considered good indicators of habitat quality because of their sensitivity to human disturbance and environmental contamination (Newton 1979; Taylor 1984). Population declines of some raptor species indicate dysfunctional ecosystems because population dynamics of top-order predators often reflect the nature of the ecosystems they inhabit (Newton 1979; Greene 1988; Olendorff et al. 1989; Burnham et al. 1990; Terborgh 1992). Thus, it has been recommended that raptors should be included in the management and conservation plans of any region, especially for threatened habitats (Olendorff et al. 1989; Burnham et al. 1990). The use of raptors as indicator species has been particularly advocated for tropical forests (Thiollay 1989, 1996). Their role as indicators of habitat naturalness in Neotropical areas, however, remains controversial. Raptors may benefit from some human activities (Vannini 1989; Bird et al. 1996). Some raptors may be opportunistic when habitat changes occur because new feeding sources and nesting structures become available (Donazar et al. 1993 a ). We examined how local breeding and wintering raptor populations are affected by human activities in the desert of Baja California, until recently one of the most undisturbed areas in the world. Habitat changes have occurred along the peninsula over the last 10 years, especially in the southern part of Baja California, mostly because of increasing human activity (Masey & Palacios 1994). Because management plans for the region may include extensive land-use changes throughout Baja California (OEA-SEDESOL-INE 1993), data on the potential effects of these changes on the status and distribution of vertebrates should be considered. Because most raptors are considered sensitive species, we expected that populations of most species of raptors would be negatively affected by anthropogenic changes in the environment.