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. https://www.spidertattooz.com/Metabo-HPT-NT1865DMASTM-18V-MV-15-Gauge-Brushless-Cordless-Angled-Finish-Nailer/