As with many other species of bats, the eastern small-footed bat usually has only one offspring a year, although a few instances of twins have been noted. This k-selected reproductive strategy means that their populations are not capable of withstanding high mortality rates, making them particularly vulnerable to sudden population declines. Mating most often occurs in autumn and the female stores the male's sperm throughout hibernation in the winter. Fertilization occurs in the spring once the females are active again, and gestation occurs between 50–60 days with young being born in late May and early June. Mating has also been noted to occur throughout the hibernation period, if individuals are awake. During the time of breeding, large number of bats come together in a behavior commonly known as "swarming." All bats of this genus are polyandrous, meaning they mate with multiple partners throughout the mating period. This mating behavior allows them to increase the likelihood of copulation, and therefore increase their reproductive success.