For such tiny animals, bats are formidable hunters. The hoary bat is most active about 5 hours after sunset (1) and may cover as much as 39 kilometres while foraging (3). Despite its generally solitary nature, the hoary bat will often form groups when hunting (1) (2). It uses echolocation to detect its prey, which usually consists of insects, particularly moths (2) (4) (7).
Although some hoary bats remain in northern areas and hibernate during winter, most appear to be migratory, travelling south at the end of the North American summer to spend the winter in warmer tropical areas (2) (3). This species migrates some of the longest distances of any bat (4). When returning north in the early spring, the female hoary bats begin migrating about a month earlier than the males (7).
The hoary bat usually mates in autumn, around the time of migration. However, after mating the female hoary bat is able to store sperm over the winter, with fertilisation not occurring until the spring, before the northward migration (2) (4). Outside of the mating season, the hoary bat is usually solitary, and males and females are rarely found together. However, the migration is one of the few times this species may form groups (2) (3) (4) (7).
The female hoary bat gives birth between May and July, usually to twins, but sometimes to up to four young. The young bats cling to the female or to a branch until old enough to fly, at around 33 days after birth (2) (4). The hoary bat is likely to live for up to six or seven years (4).