Energy balance; choices between energy spend on migration and mating influences the life cycle of the pond bat (Myotis dasycneme)

During autumn in the temperate zone, insectivorous male bats face a profound energetic challenge, as in the same period they have to make energy choices related to hibernation, mating and migration. We found evidence by looking at biometric measurements that male pond bats ( Myotis dasycneme ) are pre-occupied with mating and lose weight, while simultaneously females are accumulating fat. Our purpose was to characterize the known hibernacula in terms of male or female bias, and subsequently compare their population trend during two study periods, between 1930-1980 and 1980-2015. Our findings include evidence of colonisation of winter roosts in formerly unoccupied areas and consequently a change in the migration patterns of the male population of this species. As male bats do not assist to raise their offspring, males have abundant time to restore their energy balance after hibernation. Our results suggest that choosing a hibernacula closer to the summer habitat not only decreases energy cost needed for migration, it also lengthens the mating season and presumably also has the additional advantage of increased paternity. Additionally, these findings have important conservation implications, as male and female biased hibernation assemblages may differ critically in terms of microclimate preferences.