We studied nocturnal activity in adult male Myotis daubentonii from mid-May to early September of the years 1998–2003 in a male-dominated population in central Germany. Departure from roost after sunset, nocturnal activity time, time spent foraging, and return to roost before sunrise were recorded in radio-tracked animals during four observation periods (1: 14 May – 6 June, 2: 16 June – 10 July, 3: 22 July – 14 August, 4: 23 August – 2 September). Only three males (two in period 1, one in period 4) stayed in the day roost all night. The other tracked animals left their day-roost for the first time between 25 and 220 minutes after sunset, and their last arrival at the day-roost occurred between 2 and 545 minutes before sunrise. Bats spent most of their nocturnal activity time foraging (overall mean: 79.7 % of nocturnal activity time). Duration of nocturnal activity and nightly foraging time varied considerably over the four observation periods and were most extended in mid-summer (period 3). This is a time of high spermatogenetic activity and steep increase in body mass (built-up of fat reserves), which leads to a particularly high food demand of male Daubenton’s bats during this period of the year. Our results of an increased foraging activity during mid-summer provide evidence in support of the view that food demand of male Daubenton’s bats is indeed highest during this time of the year.