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

Abstract

Swainson's hawk (Buteo swainsoni) populations are declining in parts of their North American range, though apparently they are stable in other areas. Information on the species, ecological requirements and demographic characteristics throughout its distribution are needed to understand changes that affect its local status. In 1979 and 19851986, Swainson's hawks in the Mapimí desert in northern México nested on the top of 24 m high mesquite and yucca trees in "playas" (flat valleys). Dominant vegetation associations around the nests were species of ProsopisLarrea and ProsopisFouquieriaYucca. The first three factors of a principal component analysis explained 90% of the total variance, showing that topography, nest-tree structure, and distance to human activity were the factors most correlated with the presence of nests. Swainson's hawks in Mapimí fed mainly on ground squirrels (Spermophilus spp.), lizards (Phrynosoma spp. and Sceloporus spp.), and some groups of invertebrates (Coleoptera, Orthoptera). Prey and nest-site availability may be responsible for the high density and productivity of Swainson's hawk in the Mapimí desert.