Swarming is a behavior exhibited by temperate zone bat species in the autumn in which bats congregate and engage in chaotic flight, often chasing conspecifics. To date, swarming has been associated with species that hibernate in caves with proposed explanations including mating, investigation of potential hibernation sites, and information sharing. Male bats tend to predominate at swarming sites. Hoary bats (Lasiurus cinereus) roost solitarily in trees throughout the year and males and females are segregated during parturition and pup-rearing during the summer. Hence, they do not have conventional aggregation sites, such as caves or human-made structures, to concentrate their populations. Using year-round capture data collected during 2009- 2025 at Humboldt Redwoods State Park in northwestern California in combination with movement information and behavioral observations I demonstrate that behaviors exhibited by hoary bats are consistent with swarming behavior. Capture rates are much higher during autumn and are predominantly males, chasing behavior is observed, and intra- and inter-annual fidelity to specific capture sites occurs. Because mating in bats occurs during autumn through spring, I further propose that the primary drivers of observed swarming behavior are associated with mating.