Winter activity of bats in Mediterranean peri-urban deciduous forests

Although the Vespertilionid bats typically hibernate during the winter to minimize energy expenditure in the cold months, in the temperate regions torpor breaks can be rather frequent. The aim of our study was to conduct a preliminary characterisation of the winter bat activity patterns in Mediterranean peri-urban deciduous forests of North Portugal. Echolocation calls were recorded between November and February, and bat activity was regularly detected on warm evenings, with sun set temperatures above 4.6 degrees C during the night sampling, mostly in November (89.9%), only rarely in December (3.7%) and February (6.4%) and without activity detected in January. The most commonly recorded species were Pipistrellus pygmaeus, P. pipistrellus, and P. kuhlii. Socialization activity was mostly concentrated in November (96.8%), only with rare records in February (3.2%) and absent in December and January. Regarding the best fitting average model, obtained by the Multi-Model Inference (MMI) method to explaining the variation of bat passes, the main positive influencing factors are related with the night period of the monitoring process and temperature, and the negative influence with the precipitation recorded in the last 48 hours before surveys. The MMI results for the variation of social calls revealed as significant positive influences the humidity, temperature and wind speed and as negative influence the precipitation recorded in the last 48 hours before surveys. We outline our study as a promising baseline to the studies of winter bat activity, demonstrating how the present and past weather conditions can play a major role in bat torpor breaks. Therefore, for conservation purposes, further winter acoustic research efforts should be consider mandatory for full understanding the bat activity patterns facing the potential impacts of global climatic changes expected to occur in the Mediterranean region.