Nestbox cameras reveal geographic, temporal and sex-specific variations in the composition of provisioned prey for a declining farmland raptor

Understanding the foraging ecology of the rapidly declining little owl (Athene noctua), which faces food limitations during the breeding season, is crucial for its effective conservation and management. We assessed the composition of prey provisioned to nestlings using nestbox cameras from 2002-2022 in three countries with different landscape structures (the Czech Republic, Slovakia and the Netherlands). We particularly explored the effect of region (country), nesting stage and parental sex on prey composition. From 41,342 identified prey items, insects predominated the little owl's diet (75.6%), followed by earthworms (19%) and a smaller proportion of vertebrates (mammals and birds). The highest proportion of insects was found in the Netherlands (80.9%), whereas earthworms dominated in Slovakia (79.8%). Vertebrates (particularly small mammals) were important prey delivered during the incubation and early nesting stages, and the representation of insects increased with the progression of the breeding season. Representation of earthworms was highest in the late nesting stage. Females provisioned a higher percentage of earthworms, whereas males provisioned more vertebrates. In conclusion, the little owl's diet during the breeding season comprises a surprisingly high proportion of invertebrates. Further, differences in prey provided are most likely driven by climatic factors, habitat structure and land-use histories (causing differences between countries), different energy requirements and seasonal changes in prey availability (causing differences during individual nesting stages) and sex-specific foraging strategies and parental roles (causing differences between sexes). Conservation activities should focus on restoration and suitable management of different high-quality habitats to enhance the availability and representation of different prey taxa within little owls' territories.