Raptor habitat associations in the northern Chihuahuan Desert

The Chihuahuan Desert is among the relatively biologically diverse desert ecoregions worldwide. However, there has been a considerable transition in vegetation communities since around the mid 1800s. The most notable transition has been a shift from perennial grasslands to shrublands. Rangeland degradation has undesirable effects, such as decreased livestock and wildlife forage, increased erosion, and decreased biodiversity. Published literature is limited regarding raptor habitat associations in northern Mexico, especially in the Chihuahuan Desert. We conducted raptor surveys in 1998-99 in 68 survey tracts of various sizes (31.1+1.5 km2) placed randomly in proportion to seven dominant vegetation communities within a 160-km belt south of the U.S./ Mexico border in northern Chihuahua, Mexico. Each tract was surveyed systematically for raptorial birds. Vegetation communities were broadly classified into four grass-dominated and three shrub-dominated types. Raptor habitat association was examined through frequency of occurrence of raptors observed in the survey tracts. Eighteen raptorial species were identified during the surveys. Swainson's hawks (Buteo swainsoni), red-tailed hawks (B. jamaicensis), ravens (Corvus spp.), turkey vultures (Cathartes aura ), kestrels (Falco sparverius), and loggerhead shrikes (Lanius ludovicianus) were distributed across the seven vegetation types examined. Aplomado falcons (F. femoralis) and burrowing owls (Athene cunicularia) displayed associations with most vegetation types, however, their associations were strongest with grass-dominated communities. Typically, grassland-dominated communities hosted the highest raptor diversity. Of the 18 raptorial species observed, none demonstrated an affinity to only shrub-dominated communities. Grassland communities in the northern Chihuahua Desert are important for many raptorial species, including endangered species such as the aplomado falcon