Winter Activity of Bats in a Peri-Urban Forest: How Do Climatic Conditions Matter?

Bat activity during winter is perhaps the least documented aspect of their annual behaviour, with few observations of bats leaving their hibernation sites. In this study, we report on bat activity outside hibernacula in a peri-urban forest in France over a period of 52 nights in 2023. We considered 13 climatic variables encompassing temperature, wind, rain, and natural light variations during the night. Five bat species were detected using automatic recorders and identified manually: Myotis brandtii, Nyctalus noctula, Pipistrellus pipistrellus, P. kuhlii, and Plecotus auritus. The most active species was P. pipistrellus, accounting for 95.6% of the total number of contacts, and was therefore the sole species analyzed in detail. The main peaks of activity were observed on warmer nights; however, bat calls were also recorded during colder nights, with activity detected at a minimum temperature of -3.4°C and a mean of -1.9°C. Temperature emerged as the most significant climatic variable positively influencing bat activity, while rain had a notably negative impact. Other variables, such as wind and luminosity, appeared to have minimal or no effect. We also compared our climatic data (temperature and precipitation) with historical records from 1991–2020. This comparison revealed an increase in extreme temperature events and fluctuations, which are known to negatively impact bat populations. Nevertheless, P. pipistrellus in northern France may be less affected by these changes due to its tolerance of climate variability and its use of diverse roosting sites. Further research across different locations and time periods would help validate and refine these findings, providing a clearer understanding of the effects of global warming on bat ecology and populations.