Main Causes of Bat Mortality Obtained Through Admission to Rescue Centres

Bats have decreasing population trends around the world, and knowledge on the causes for this decline is the first step to improving conservation and management strategies to restore their populations. An important source of data for the study of the causes of bat mortality is the admissions to rescue centres. The aim of this work was to identify the different causes of bat admissions to rescue centres in Castilla y León (Spain) over more than 30 years, analyzing the importance of the threats for different species, as well as the tendency of anthropogenic causes over the years, such as the increase in industrial wind-power facilities. The dataset included 791 bats (568 dead and 223 injured). The species with the largest number of entries was Pipistrellus pipistrellus at 451, followed by 82 Hypsugo savii, 64 Plecotus sp., 63 Tadarida teniotis, 42 Eptesicus serotinus and 24 Nyctalus lasiopterus. The most important known causes of entry for these selected species were collisions with wind turbines (n = 160); immaturity-related causes (e.g., orphan individuals with insufficient foraging and flight skills prone to injury or starvation) (n = 93); weakness due to starvation (n = 75); trauma: blow of unknown origin (n = 69); shooting: vandalism with a gun (n = 15); carnivore bite: predation (n = 8); road kill: road accident (n = 3); and disease: sickness (n = 3). In addition, there were many admissions which lacked a known cause (n = 294). The species with the most carcasses for collisions with wind turbines was Pipistrellus pipistrellus at 100, followed by 40 Hypsugo savii and 15 Nyctalus lasiopterus. As expected, the number of bats that collided with wind turbines showed a significant temporal correlation with the number of wind farms deployed in the territory, and they mainly occurred in September and October, as has also been found in other studies.