Long-Eared Owls (Asio otus) Prey on Roosting Flocks of Fieldfares (Turdus pilaris)

Long-eared Owls (Asio otus) frequently inhabit humanaltered landscapes, including residential areas in cities, where they usually breed in nests of corvids, and roost communally on trees during the autumn and winter (Pirovano et al. 2000, König and Weick 2008). Winter roosting sites are often located in urban/suburban areas (Makarova and Sharikov 2015) and can hold several hundred individuals (up to approximately 400 individuals; Ružić et al. 2009). Although Long-eared Owls have widely varying diets, they are considered specialist predators that prey primarily on small mammals (e.g., Microtus voles, Apodemus mice). Most studies conducted in Europe have concluded that small mammals are the most important prey of this species (Nilsson 1981, Escala et al. 2009, Dziemian et al. 2012) and can make up to 93% of the prey consumed (Birrer 2009). Pellet analyses usually document a very low proportion and occasional rather than regular occurrence of birds in the owls’ diet (e.g., Romanowski and Zmihorski 2008). In most cases, these were small-bodied passerines such as tits (Paridae), sparrows (Passeridae), and finches (Fringillidae), and larger birds were incidental (Sándor and Kiss 2008). Owls wintering in cities usually hunt outside the settlements in grasslands, agricultural areas, or shrubby habitats (Tulis et al. 2019). However, unfavorable weather conditions and/or rapid changes in small mammal prey communities may change the hunting behavior and strategies of owls (Canova 1989). We here report and discuss an observation of unusual prey selection and hunting behavior in the Long-eared Owl. Our observations took place in Sombor, a town in northwestern Serbia (southeastern Europe) with semicontinental climate and a human population of approximately 48,000 inhabitants (Mér} o and Žuljević 2010). During 27 February to 6 March 2018, temperatures were considerably colder than average, with lowest daily mean temperature around –108C (on average, mean lowest temperature is approximately –0.78C); the minimum temperature on 1 March was –258C. Approximately 15 cm of snow covered the region. Trees planted along avenues, in parks, and in gardens of private residences provide the major vegetative cover in the town; common deciduous species include common hackberry (Celtis occidentalis), London plane tree (Platanus 3 acerifolia), horse chestnut (Aesculus hippocastanum), and Japanese pagoda-tree (Sophora japonica). Gardens often contain coniferous trees (Mér} o and Žuljević 2010). In the gardens of the study site (banding locality) and the surrounding gardens, the most frequently planted tree species are pines (Pinus spp.), black locust (Robinia pseudoacacia), and elder (Sambucus nigra). Monitoring of Long-eared Owls wintering in Sombor started in winter 2014/2015. Every winter, between 120 and 150 Long-eared Owls roost in the center of Sombor (Mér} o and Žuljević 2010). We observed the behavior and movement of owls, captured them, and banded them with aluminum rings between November and March each winter. Our banding localities (n 1⁄4 8; Mér} o and Žuljević 2020) were in larger gardens with open areas in the urban and semi-urban regions of the town. We used mist nets to 1 Email address: thomas.oliver. mero@gmail.com