Hibernation phenology of Myotis lucifugus

Hibernating animals must time immergence and emergence carefully to maximize reproductive success and reduce the risk of encountering inclement weather or predators. Few studies of phenology exist for any hibernating species and those that do address species which mate during spring. We used passive transponders (PIT tags) to study hibernation phenology of little brown bats Myotis lucifugus, a species that mates prior to hibernation in the fall. We expected that adult females would emerge earliest as early parturition increases juvenile survival. We predicted that females with large fat stores should emerge earliest because of their ability to tolerate inclement spring weather at the maternity roost. We also predicted that adult males would remain active later than females to maximize mating opportunities and compensate for body mass decline during the mating period. We implanted 475 bats with PIT tags and remotely recorded immergence and emergence timing at a hibernaculum in central Canada. As expected, adult males were active significantly later (median immergence date = 16 September 2011) than adult females (11 September 2011) and adult females emerged earlier (median emergence date = 6 May 2012) than both adult males (25 May 2012) and subadults (13 May 2012). Emergence timing was correlated with fall body condition in adult females, with fatter females emerging earlier, but not males. Our results highlight the importance of reproductive timing as an influence on hibernation phenology of mammals.