Energetic trade-offs of hibernation at historical and new ranges in the common noctule (Nyctalus noctula)

The common noctule (Nyctalus noctula) is a European bat that traditionally migrates from its summer sites to hibernate at lower latitudes. In the last three decades, common noctules started to hibernate at higher latitudes than before. Changing climate conditions could be driving this northern extension of the hibernation range. It is thus crucial to uncover how climatic variables affect noctule hibernation. Furthermore, as population trends for this species are mostly unknown but seem to be decreasing at some sites and increasing at others, it is important to assess whether these new wintering ranges offer suitable conditions for hibernation. To assess this, we need to monitor roost temperatures and quantify the energy balance during hibernation across different latitudes. Noctules are known to arouse and even leave their roosts during winter. Local conditions may determine how often these energetically costly arousals occur. At the same time, winter flights must likely be met by food intake. I will employ passive acoustic monitoring and non-invasive fecal sampling at different latitudes to link climatic variables to activity and food availability during winter. Additionally, I will monitor activity, energy expenditure and temperature of individual bats via tagging. Finally, I will model noctule population trends across Europe. To do this, I am collecting longitudinal population data from collaborators. The results of this research will reveal the consequences of a climate-induced range shift on a traditionally common bat species whose current population trends are unknown, informing about its future distribution and the potential consequences for our ecosystems.