干旱区生态环境知识资源中心

Based on cranial measurements we estimated the size- and age-class (juvenile or adult) of leaf-eared mice (Phyllotis darwini) consumed by great horned (Bubo virginianus) and barn owls (Tyto alba) during 1990-92 in a semiarid locality of northcentral Chile. We compared this information to that obtained from mice live-trapped at the same place and period. The frequency distributions of body weights of leaf-eared mice consumed by the two owl species was not statistically different, despite the four-fold difference in body size and different hunting mode of the two owls. In two out of three breeding seasons the owls preyed more frequently on adult mice. In the remaining breeding season and the three wintering seasons they preyed upon adults and juveniles in about the same proportion as they were live-trapped in the field. The higher predation on adult individuals (reproductive) was associated to a greater mobility of adult versus juvenile mice, which may render the former more vulnerable to owl detection.