Breeding success, nest-site characteristics, and diet of Swainson's hawk (Buteo swainsoni) in a stable population in northern Mexico

Swainson's hawk (Buteo swainsoni) populations are declining in parts of the ir North American range, though apparently they are stable in other areas. Information on the species, ecological requirements and demographic charact eristics throughout its distribution are needed to understand changes that affect its local status. In 1979 and 1985-1986, Swainson's hawks in the Map imi desert in northern Mexico nested on the top of 2-4 m high mesquite and yucca trees in "playas" (flat valleys). Dominant vegetation associations ar ound the nests were species of Prosopis-Larrea and Prosopis-Fouquieria-Yucc a. The first three factors of a principal component analysis explained 90% of the total variance, showing that topography, nest-tree structure, and di stance to human activity were the factors most correlated with the presence of nests. Swainson's hawks in Mapimi fed mainly on ground squirrels (Sperm ophilus spp.), lizards (Phrynosoma spp. and Sceloporus spp.), and some grou ps of invertebrates (Coleoptera, Orthoptera). Prey and nest-site availabili ty may be responsible for the high density and productivity of Swainson's h awk in the Mapimi desert.