The sessile serotine:: the influence of roost temperature on philopatry and reproductive phenology of Eptesicus serotinus (Schreber, 1774) (Mammalia: Chiroptera)

Maternity colonies of serotine bats inhabiting large roof spaces were studied at three localities in southwestern Germany and Luxembourg. Bats of all three colonies featured to the maternity roosts during the second or third week of April and were strongly philopatric to their main roost. Roost switching occurred only rarely and for short periods. Measurements of temperature inside two roosts showed gradients according to height and aspect of the roof space with a mean roost temperature of 22 degrees C gestation and lactation. The availability of adequate microclimates within the roost during gestation and lactation was thought to favour roost philopatry. Females of all ages and reproductive classes inhabit the roosts throughout Summer. Mean (+/- SD) inferred gestation length was 52 +/- 6 days, and variations were not related to roost tempertures during gestation. The mean date of birth was 16th June With most births occuring within a period of 14 +/- 6 days and of young first emerged from the roost 36 7 days after birth. Prolonged adverse weather conditions, leading, to low roost temperatures. resulted in mortality of 11-27% of preweaning young in four of the five years studied. Since immigration occurs the number of young emerging from the roost cannot he deduced from the number of females present during, gestation or lactation. Adult females and young start to disperse after the first young are weaned at the beginning, of August and are last observed in October. The implications of these results for the epidemiology of European bat lyssavirus I are discussed.