Bats seek roosts that provide a warm environment and allow them to retain body heat, stay hydrated and maximize pup growth to raise offspring. Conditions that are too warm risk heat stress and can lead to death, especially for pups who can’t yet fly. Those that are too cool require bats to burn body fat and can reduce pup growth rates and survival rates. Just a degree or two can make the difference.

For this reason, it’s normal for bats to periodically switch roosts or switch positions within a roost in order to find the right conditions. For species that roost in buildings or structures, bat boxes can provide roost habitat as long as they are designed appropriately. 

Bat species that roost in groups (known as colonies) may use bat houses to seek shelter from predators and protection from weather elements such as rain, wind and direct sunlight. There are 16 species in North America that roost colonially, and it’s likely (but not guaranteed) that you live within range of at least one of them – the big brown bat, the little brown bat, and the Yuma myotis are widely distributed across portions of North America and frequently use bat boxes.

Bat houses are not typically used in winter and don’t provide the appropriate conditions for hibernation. In areas of North America with warm year-round temperatures, bat houses may have some level of year-round use. Large aggregations of bats during warm months are almost always made up of pregnant and nursing females who return year after year to these colonies. Smaller numbers of bats are likely to be males and non-reproductive females during warm months, or migratory bats making seasonal long-distance movements between summer and winter habitats during the ‘shoulder season’.

Bats need a variety of microclimates to support their needs throughout the pup-rearing season and across a range of temperatures and conditions. If there are existing boxes or roosts in your area, take note of their solar exposure and placement and consider offering something different but complementary in the placement of your boxes. If there are no suitable roosting conditions nearby, your boxes may provide the only available roosting habitat for bats, and it will be extremely important that your design accommodate a range of microclimates suitable for different weather conditions. Consider placements in full sun and in shade to meet their needs across the pup-rearing season.

Multi-chamber maternity bat boxes with venting are best for providing bats with a range of microclimates. Avoid small bat houses (the size of a typical bird house) and large single chamber boxes, which may not provide a suitable gradient of temperatures inside, nor enough mass to retain heat at night. If installing a single box, choose a multi-chamber box (four or more) that is taller than it is wide, and includes venting to create cool areas or escape zones that can be used during heat waves.

Bats should never be ‘bulging out’ of the bottom of the box, fanning wings, or flying during the day. These are signs that temperatures in the box are causing heat stress. If you see pups falling out of the box, reach out to your local bat rehabber for advice and consider installing a temporary awning or shade. Over the long-term, you may need to install another box nearby that is more shaded or is painted a lighter color. 

If you are trying to replace habitat for bats that is being lost due to bat exclusion or demolition, it is very important that you first identify how many bats you are trying to house, and plan well in advance to make sure the replacement structures are in place before demolitions or exclusions begin. Larger bat houses or bat condos may be necessary to accommodate large numbers of bats. Exclusions should never occur during the maternity season (typically May 15-August 15) and local laws may protect bats that occupy buildings. Your state bat biologist will be familiar with restrictions on timing or method of removal and will be a helpful point of contact if you are working to relocate a large colony.

Consider this an opportunity to work with your community or neighbors! Although multiple bat boxes can be an expensive endeavor for one person, a commitment from several neighbors can help you to sufficiently replace lost roosting habitat from a building exclusion.

Bat boxes that are installed for reasons other accommodating displaced bats can take up to five years to become occupied. However, bats that have been excluded or those that have lost their roost due to demolition or fire may immediately take up alternate roosts in the season following roost loss. 

Visit our pro tips page for tips on materials, size and placement.

Ideally, bat houses should be installed in an area at the beginning of the summer prior to any bat exclusion work. If you are adding new roosts, it can be helpful to monitor sun exposure, shade and temperature conditions over the course of a season before choosing installation locations.

Check your boxes at least once a year for any necessary routine maintenance such as caulking, repainting, and cleaning out abandoned wasps nests. Because bats often return year after year to the same maternity roosts, they may continue to use sub-optimal roosts that compromise reproductive success. For this reason, stewardship and monitoring is an important part of being a responsible bat box owner. 

If you decide that a bat box is right for your yard or community, consider these pro tips for selecting or building the right box. More information can be found in these Best Management Practices for the Use of Bat Houses in the U.S. and Canada.

Remember to never touch or handle a bat directly. Use heavy leather work gloves when following capture guidelines.