Comparative food habits of Bubo owls in Mediterranean-type ecosystems.

Abstract

Tested whether food habits of Bubo owls were more similar among mediterranean-type ecosystems (shrublands in Chile, Spain, and California) compared to those in a different ecosystem (a grassland in Colorado), by estimating the diet diversity at both the class and species level of mammalian prey, and the mean weight of mammalian prey in the diet. These owls in all 4 areas did not differ markedly in their diet composition; they all preyed heavily on rabbits, little on mammals weighing <20 g, and somewhat on other vertebrates as well as large invertebrates. They did, however, differ in their diet diversity. At the class level of prey selection, Spanish Bubo were most diverse and Colorado Bubo the least (a 3-fold difference) . At the mammalian species level, Spanish Bubo were the least diverse and both Chilean and Californian Bubo the most diverse (c2.6 times higher). These owls also differed markedly in the mean weight of mammal prey in their diet. Spanish Bubo had the highest mean value, whereas California Bubo took mammals on average almost 6 times smaller. Weights of available categories of mammal prey did not differ among regions. Differences in the weights of prey taken by owls apparently reflect differential abundance of local mammals. The owl assemblages in the 4 regions are similar in both taxonomic composition and configuration of owl sizes. Sympatric Athene and Tyto owls do not closely parallel the dietary trends seen in Bubo. -from Authors