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.

捕食者物种的共存通常依赖于能够通过时空生态位分化降低种间竞争的行为或食性偏好。本研究针对保加利亚东南部某农业景观中共存的仓鸮（*Tyto alba*）与雕鸮（*Bubo bubo*）的食性展开对比分析。白齿鼩（*Crocidura* 属）、田鼠（*Microtus* 属）与小家鼠（*Mus* 属）为仓鸮的主要猎物，按数量占比达86.3%，按生物量占比达81.2%，且其在仓鸮年度食性中的出现频率存在显著差异。雕鸮年度食性中占主导的食物生物量（64.8 ± 6.2%）来自体型更大的猎物，包括白腹刺猬（*Erinaceus roumanicus*）、欧洲野兔（*Lepus europaeus*）以及湿地与开阔生境中的非雀形目鸟类。两种鸮类在同一领地内偏好并捕猎不同体型组的猎物，这一差异使得二者的食物竞争水平极低——按猎物生物量计算的食性重叠度仅为6.0 ± 3.6%。田鼠是两种鸮类的年度食性中唯一在种内对比中出现频率存在显著差异的猎物；研究期间，两种鸮的食性中田鼠的占比均呈现相似的变化趋势。尽管雕鸮面临较高的食物压力，但其对仓鸮的捕食行为仅因二者的同域繁殖受到轻微影响。本研究结果揭示了食性偏好如何助力预测具有潜在竞争关系的捕食者物种能否实现成功共存。