Abstract
The winter activity of bats was studied in an area of Bavaria, Southern Germany, for seven consecutive years (2007–2013). Echolocation calls were recorded in known foraging areas between October and March of each winter, and bats were regularly seen on evenings with temperatures above +6 °C, except for the period between mid-December and mid-February, when even bouts of warm weather did not appear to trigger foraging activity. Below +3 °C no bats appeared in the foraging areas. The most frequently recorded species were Nyctalus noctula, Pipistrellus pipistrellus, Pipistrellus nathusii and Vespertilio murinus. Final buzzes indicating attempts to catch prey were recorded for these species even in December and February, which supports the idea that the bats were not only in search of water or just moving between roosts. Myotis species, on the other hand, which hibernate in roosts offering more constant temperature conditions, were not observed at all between mid-November and March. Further investigations have to show whether warmer winter evenings offer bats an opportunity for casual hunting or whether winter foraging expresses an urgent need for weak individuals.