Long-eared owl Asio otus is a specialist predator, hunting primarily upon voles Microtus spp. Be-cause size of the territory and breeding success of the predator depend on food availability, the number of long-eared owls wintering in a given locality is likely determined by the local abun-dance of voles. The amplitude and regularity of their cycle have been recently diminished and quantitative assessment of such a cycle is currently unavailable. Diet and number of wintering owls were monitored during two winters (2005/06 and 2006/07) in Busko-Zdrój and Pińczów (south-central Poland). It was found that number of voles is still a factor determining number of wintering owls, also every fock in particular locality has its’ own dynamics of owl number. Research on predators’ diet − especially specialists like long-eared owl − is nowadays very important because of vole fluctuation cycle disturbances caused mainly by global warming.
