Long-Term Dynamics of Long-Eared OwlsAsio otusat a Northern Winter Roost in European Russia

Abstract

We investigated the factors influencing the dynamics of Long-eared Owls Asio otus wintering in Moscow. The study was carried out in 2001–2011. Twelve communal roosts and 14 solitary wintering owls were found. Number of active roosts was positively correlated with the total number of wintering owls per year. The four largest roosts were active for many years, with up to 16 individuals in a single winter (9.9 ± 1.3 on average). Generalized linear models indicated that the number of wintering owls was influenced simultaneously by the abundance of Common Vole Microtus arvalis in the previous autumn and in spring, and the owls' breeding numbers in the study plot. The most important factor was vole abundance in early spring indirectly indicating food supply in late winter. The influence of weather was investigated on the regularly surveyed local site in Moscow. The maximum number of owls at the roosting site varied from 0 to 9 individuals (2.1 ± 0.4 on average). Among weather factors, the most important influence on the dynamics of owls was by snow cover and wind jointly, though the snow was undoubtedly of greatest significance. Air temperature and precipitation turned out to be almost of no importance for owl dynamics at the roosting site.