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 (Tyto alba) and eagle owls (Bubo bubo) in
an agricultural landscape of SE Bulgaria were compared. White-toothed shrews (Crocidura
spp.), voles (Microtus spp.) and mice (Mus 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 (Erinaceus roumanicus), European hare (Lepus
europaeus) 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.

捕食物种的共存往往取决于导致空间时间竞争减少的行为或偏好。在本研究中，对比了东南保加利亚农业景观中同域存在的仓鸮（Tyto alba）和雕鸮（Bubo bubo）的饮食。白牙鼠（Crocidura spp.）、田鼠（Microtus spp.）和老鼠（Mus spp.）是仓鸮的主要猎物（数量占比86.3%，生物量占比81.2%），其在年度饮食中的出现频率存在显著差异。雕鸮年度饮食中显著不同的主要生物量（64.8 ± 6.2%）由如白胸刺猬（Erinaceus roumanicus）、欧洲野兔（Lepus europaeus）和湿地及开阔栖息地非鸣禽等体型更大的猎物组成。两种猫头鹰物种在同一领地内偏爱并猎捕不同体型大小的猎物群体，这种差异解释了低水平的食物竞争（根据猎物生物量计算，饮食重叠率为6.0 ± 3.6%）。在物种内比较中，田鼠是两种猫头鹰唯一在年度饮食中具有显著不同出现频率的猎物。在研究期间，两种饮食中田鼠的比例显示出相似的趋势。尽管雕鸮与仓鸮共存繁殖导致食物压力水平较高，但雕鸮对仓鸮的捕食仍受到轻微影响。这些发现有助于揭示捕食习性如何预测潜在竞争性捕食物种的成功共存。