From PLOS One:
Bats Swarm Where They Hibernate: Compositional Similarity between Autumn Swarming and Winter Hibernation Assemblages at Five Underground Sites
Jaap van Schaik, René Janssen, Thijs Bosch, Anne-Jifke Haarsma, Jasja J. A. Dekker, Bart Kranstauber
During autumn in the temperate zone of both the new and old world, bats of many species assemble at underground sites in a behaviour known as swarming. Autumn swarming behaviour is thought to primarily serve as a promiscuous mating system, but may also be related to the localization and assessment of hibernacula. Bats subsequently make use of the same underground sites during winter hibernation, however it is currently unknown if the assemblages that make use of a site are comparable across swarming and hibernation seasons.
Our purpose was to characterize the bat assemblages found at five underground sites during both the swarming and the hibernation season and compare the assemblages found during the two seasons both across sites and within species. We found that the relative abundance of individual species per site, as well as the relative proportion of a species that makes use of each site, were both significantly correlated between the swarming and hibernation seasons. These results suggest that swarming may indeed play a role in the localization of suitable hibernation sites. Additionally, these findings have important conservation implications, as this correlation can be used to improve monitoring of underground sites and predict the importance of certain sites for rare and cryptic bat species.
WWII ALMOST INVOLVED A BAT BOMB “Imagine: a quiet, tense night in the middle of wartime. A plane rips through the air above your city, rupturing the stillness. The bay doors open, and out whistles a bomb. It drops and drops. Everyone braces. But when it explodes, the city is filled not with the flash of impact, but with hundreds and hundreds of tiny, whirling bats. This ridiculous vision — in which Japanese cities were destroyed by a giant bomb full of bats that were themselves carrying tinier bombs — was called Project X-Ray, and it was but a claw’s breadth from becoming a reality.” [Atlas Obscura]