Activity patterns of the serotine bat ( Eptesicus serotinus ) at a roost in southern England

Activity patterns and emergence times of a colony of serotine bats, Eptesicus serotinus , were studied in southern England. Time of emergence from the day roost varied over the summer but was strongly correlated with sunset. Mean emergence time was 11.6 ± 7.7 min after sunset. Early in summer, activity patterns were unimodal, becoming bimodal during mid‐ to late pregnancy and multimodal in early to mid‐lactation. When juveniles were volant, activity patterns became unimodal again. Periods of low ambient temperature were associated with reduced activity. The duration of the first foraging flight decreased as pregnancy progressed, possibly as a result of the greater wing‐loading caused by increased body mass. However, the first foraging flight increased in duration during the course of lactation, probably in response to a combination of increased night length and the increased energetic demands of milk production. It is concluded that seasonal variation in the length of time spent away from the roost in the serotine is related to reproductive status, night length and ambient temperature. It is suggested that the more northerly distribution of this bat in continental Europe may be due to differences in habitat use and diet.