The relationship between intra–guild diet overlap and breeding in owls in Israel

Abstract

Even though intra-guild predators frequently prey on the same species, it is unclear whether diet overlap between two predators is a source of interspecific competition or whether predators simply use the same abundant prey resource. We measured the extent to which the diets of barn owls (Tyto alba) and long-eared owls (Asio otus) in Israel overlap and examined whether yearly differences in diet overlap correlate with barn owl breeding success. Pianka’s index of niche overlap was positively related to barn owl population size but not to its breeding success. The number of breeding barn owls was higher when long-eared owls consumed more rodents, suggesting that diet overlap most likely increased when rodents became more abundant. Therefore, in Israel, when these two owl species prey more often on rodents, their diets are more similar and interspecific competition is reduced. Unlike sympatric populations in Europe, in years when rodents are less abundant in Israel long-eared owls switch to hunting alternative prey (e.g., birds), perhaps to avoid competition with barn owls.