Local concentration of foraging noctule bats (Nyctalus noctula) as a possible tool to assess the density of bats in large forest complexes

Concentrations of at least 600 hunting noctule bats Nyctalus noctula were observed over the artificial shallow reservoir Siemianówka in eastern Poland. The observation indicates that noctule bats concentrate hunting during the presence of vast amounts of insects over the reservoir. We suggest that the high concentrations of noctule bats provide a potential tool for the estimation of local population size or density in large forest complexes.