Reproductive condition and activity pattern of male Daubenton's bats (Myotis daubentonii) in the summer habitat

We studied temporal variation in epididymal fitting (a measure of reproductive condition) and activity pattern of male Daubenton's bats (Myotis daubentonii) in a summer habitat near Staufenberg (Hesse, Germany). Epididymal fitting in adult males declined from April to early July. Thereafter epididymal filling sharply increased and the highest median value was reached in the second half of September, i.e., prior to the occupation of the hibernaculum. Highest median epididymal filling in juveniles occurred in the first half of September. During August, September and October epididymal fitting of adult mates was significantly higher than that of juveniles. In Late summer (August/September) relatively heavy adult mates stayed significantly longer in their day roosts and spent significantly Less time foraging than in early summer (June/July). The findings suggest that a Large proportion of matings in M. daubentonii occurs already in the day roosts within the summer habitat.