Swarming of bats at different elevations in the Carpathian Mountains

Swarming bat activity was monitored at three caves at elevations ranging from 880 m to 1,907 m above sea level in the Carpathian Mountains, using an infrared light barrier with data-logger, a video camera with a night-scope system, and subsequently by mist netting. A total of 6,175 bats of 19 species was captured, and over 70,000 passes through cave openings were registered. Caves differed in bat species richness, sex ratio, abundance of particular species and species composition. Peak species richness was observed in the mid-elevation cave. Bat activity was high in all caves, but declined with increasing altitude. Swarming activity occurred earlier at high elevation than at lower elevations. Activity of boreal-alpine species, such as Eptesicus nilssonii, peaked at the start of the swarming period, that of species typical of lower elevations, such as Myotis emarginatus, peaked in the middle of the swarming season. In a few species, males showed a significant preference for higher altitude caves, in contrast to females. A similar pattern was observed in the proportion of adults to juveniles, which increased with increasing elevation. Our results also suggest that M. brandtii and M. alcathoe were more often encountered at lower elevations, M. mystacinus (sensu stricto) at higher ones.