Warmer states have an earlier maternity season, and cooler states have a slightly later maternity season. The dates vary between mid-April to early June for the beginning of the maternity season and mid to late August for the end of the maternity season.

Bat maternity season also means it’s time for bat maternity colonies, when either smaller or larger groups of pregnant bats roost together in dark, warm spaces they deem safe. And while caves are perfect for such activities, our relentless urban expansion often leaves bats with no other option than to initiate maternity colonies in abandoned buildings, or even in inhabited households.

Dealing with a bat maternity colony on your property can be noisy and smelly, and large amounts of bat guano may lead to more serious issues, including threats to your health, or even to the structure of the building they roost in. Nevertheless, the typical North American bat colony is made of approximately 40 female bats who each give birth to one pup. This means you won’t be dealing with huge quantities of bat waste.

These invading bats are most likely part of what is referred to as a maternity colony. Maternity colonies are a group of female bats that congregate to give birth and raise their young during the spring. Bat moms, grand-moms, sisters, aunts and nieces all live together as one supportive unit while the young pups (baby bats) are born and cared for. Each female has only one pup at a time. The pups are unable to fly for a few months. Most of the time, they are left in the roost while the mothers forage outside for insects. By the end of the maternity season, the pups are finally able to fly and are no longer left in the roost at night while the mothers feed.