Diet, diel activity and prey handling during food provisioning in the common barn owl (Tyto alba): a comparative study using continuous camera monitoring data from three European countries

Even though various aspects of the barn owl’s (Tyto alba) diet and breeding ecology have been extensively studied in the past, high-resolution data on diel activity and prey handling at the nest are still scarce. This study investigated food provisioning, prey handling and diel activity patterns at three barn owl nests in Spain, England, and Ireland respectively, using the method of continuous camera monitoring. I monitored one month of the nestling period from each nest using video recordings from the breeding season of 2022 and 2023, observing which prey types were delivered, prey condition, timing of delivery and how prey was handled at the nest. Of the 1500 prey deliveries observed, small mammals accounted for as much as 95% of the total, with rodents (Rodentia) comprising the largest portion (79 %) and shrews (Soricidae) the second largest portion (15%). Less than 0.7% of the total deliveries were non-mammalian prey. Observation of hunting times revealed a strictly nocturnal activity pattern. Variations in night length due to latitudinal differences enabled longer nights and subsequently more hunting hours for the barn owls at the Spanish nest compared to the English and Irish nests. Prey were delivered intact in 99 % of the instances where condition could be determined, and decapitation of prey occurred only eight times in total. The probability of prey being stored decreased with increasing nestling age for nearly all prey groups, and shrews had a lower probability of being stored than other prey groups for all ages. The probability of nestlings feeding with maternal assistance decreased with nestling age, with a 50% probability of independent feeding occurring at ages 22 days and 16 days for the English and Irish nest respectively. Delivery rates were correlated with nestling age, with the rate initially increasing before diminishing as the nestlings aged and prepared for fledging. Camera monitoring proved to be an efficient way to obtain high resolution data on the barn owl’s food provisioning behavior. My results suggest that provisioning barn owls prefer to hunt small mammals, and while usually hunting opportunistically, might have the ability to select appropriately sized prey based on the nestlings’ current swallowing capacity. Low decapitation rates further indicate that barn owl pellets are a reliable data source for diet and small mammal assessment studies and may contain less bias than pellets from other raptors. Furthermore, variations in night length across latitudes may influence hunting behavior, with southern barn owls potentially benefiting from longer hunting hours in summer. However, northern barn owls may compensate for shorter nights with higher hunting effort per hour. Future studies on barn owl foraging ecology should include latitudinal variations in night length to gain a better understanding of potential fitness implications