Functional significance of emergence timing in bats

We investigated intraspecific differences in evening emergence time of nort hern bats Eptesicus nilssonii, greater horseshoe bats Rhinolophus ferrumequ inum and lesser horseshoe bats R. hipposideros. Significant differences in emergence time were associated with presumed variation in predation risk. r elated to light intensity, and energetic benefits of early emergence, cause d by differences in age, reproductive state (energetic demands), and body c ondition. Females of both species emerged progressively later as pregnancy advanced, perhaps because of decreased flight performance, and earlier as l actation proceeded. probably because of increased energy demands and low re serves. Bats under energetic stress, due to persistent low ambient temperat ures during pregnancy, or when body reserves were tow, emerged relatively e arly, and hence appeared to take higher risks, than other bats. Young bats emerged much later than the adults at first. but progressively earlier as t heir night skills improved. Lesser horseshoe bats emerged later at exposed roost exits than in more protected situations. The results largely corrobor ate the hypothesis that emergence time, and therefore feeding performance, of insectivorous bats is constrained at bright light conditions, possibly b y predation risk (from birds), and modified by energetic considerations.