Dietary comparison of coexisting barn owl (Tyto alba) and eagle owl (Bubo bubo) during consecutive breeding seasons

Coexistence of predator species often depends on behaviours or preferences that result in spatiotemporal reduction of competition. In this study, the diets of coexisting barn owls (<i>Tyto alba</i>) and eagle owls (<i>Bubo bubo</i>) in an agricultural landscape of SE Bulgaria were compared. White-toothed shrews (<i>Crocidura </i>spp.), voles (<i>Microtus </i>spp.) and mice (<i>Mus </i>spp.) were the main prey of barn owl (86.3% by number, 81.2% by biomass) with significantly different frequencies in annual diets. The principle biomass (64.8 ± 6.2%) of the significantly different eagle owl annual diets comprised much heavier prey such as white-breasted hedgehog (<i>Erinaceus roumanicus</i>), European hare (<i>Lepus europaeus</i>) and non-passerine birds of wetlands and open habitats. The two owl species preferred and hunted on different prey size groups in the same territory, and this difference explained the low level of food competition (6.0 ± 3.6% diet overlap according to prey biomass). Voles were the only prey of the two owls with significantly different frequencies for the annual diets in intraspecies comparisons. The proportions of voles in both diets showed similar trends during the study. Eagle owl predation on barn owls was slightly affected by their coexisting breeding despite the high levels of food stress of eagle owl. These findings provide insight into how preying habits can predict successful coexistence of potentially competing predator species.