Selection of prey by size and sex in the Long-eared Owl Asio otus

Abstract

ABSTRACTCapsule: Voles predated by Long-eared Owls Asio otus were more likely to be female and smaller than the voles in the available population.Aims: Our study aimed to estimate the size and sex of prey in the diet of Long-eared Owls and compare them with the size and sex of prey in the field.Methods: The study was carried out in 2016 and 2017 at Moscow Region, Russia. Prey remains were extracted from pellets produced by Long-eared Owls. The sex of prey was identifiable due to sexual dimorphism of pelvic bones, and bone dimensions were used to estimate the body mass of prey. Small mammals were also trapped in the study area to compare the sex and size of animals taken as prey with those in the general population.Results: Long-eared Owls did not capture small mammals randomly with respect to size and sex. In general, individuals of the two main prey species in the pellets of Long-eared Owls were significantly smaller than the trapped animals. Long-eared Owls more often caught the females of both species of voles. However, the percentages of females in the diet varied between years.Conclusions: Long-eared Owls more often catch individual voles of a certain size and sex. We suggest that this selective predation could influence not only the number of prey species, but could also impact the structure of their local populations.