Bats typically roost in buildings in the warm summer months, between June and August, although they may be present earlier or later depending on the building and weather conditions. Nursery roosts (also known as maternity roosts), where mothers give birth and care for their babies, are the largest colonies. Each mother has one baby in late June or early July, which she suckles with her own milk. The number of bats in a nursery colony depends on the species of bat and how good the surrounding landscape is for providing insects. Female bats choose roosts that become very warm during the day because this increases the chance of survival for their babies. Non-breeding bats may occupy houses in smaller numbers, or even singly, and move around alot, rarely staying long in the same roost.
During winter months, bats hibernate in cool places. In Ireland there is very little known about where bats hibernate in winter although summer roosts are not usually used. Houses are usually too warm so they may choose caves, bridges, crevices in stone-outbuildings, or even tree holes.
Although bats do use dwelling houses and other buildings for roosting, they do not share their living space with humans. If you have found a bat in the living space of your house then it is there by mistake. Parts of a building where bats may roost include:
- attic/roof void
- between roof felt and slates
- behind hanging tiles
- behind soffit boards at a gable
- in wall cavities
- in crevices in roof timbers
- in wall cracks (particularly in old outbuildings).
Examples of roosting and access points for bats in buildings – click on the image to view