Are bats tracking climate change? Long-term monitoring reveals phenology shifts and population trends of forest bats

Climate change is altering wildlife assemblages, although limited long-term data hinders understanding of its impacts. Bats are widely reported to be good models for studying climate change effects due to their sensitivity to temperature and migration patterns. Here we use forest bats as models to investigate how climate and interspecific interactions may affect wildlife species in the long-term, by monitoring populations of sympatric noctules over three decades. We aimed at understanding how climate influences fluctuations in population size and phenology, as well as assessing the role of interactions among sympatric species in shaping population trends. We investigated the long-term effects of climate change on forest bat species coexisting in the same mountainous area in central Italy. Through bat-box monitoring analysis, we examined population trends, phenological changes, and potential interspecific interactions. Overall, populations of all three species exhibited a significant increase, although fluctuations were largely driven by precipitation patterns. Specifically, cumulative yearly precipitation affected population sizes of all species, with N. leisleri additionally influenced by minimum yearly temperatures and by the presence of N. lasiopterus. We also documented phenological shifts, particularly in N. leisleri, with males advancing their arrival as early as February, and females delaying to late summer and autumn, leading to a significant decline in seasonal intersex overlap. Interspecific interactions also apparently shaped population trends, with N. lasiopterus showing a positive association with N. noctula, and N. leisleri being displaced from areas with increasing presence of N. lasiopterus. These findings indicate that forest bats may alter their ecology in response to climate change, yet inconsistently among species and between sexes, with potentially negative effects upon interspecific interactions and individual reproductive success. Besides, we highlight the importance of long-term monitoring programs in understanding the multifaceted effects of climate change on bat populations in forest ecosystems, particularly in mountain habitats.