So, you’ve decided to become a friend to bats. Great choice! Bats are vital to the health of our food systems, our economies and our environment, and they are just plain fascinating to watch! And with 52% of North American bat species in need of conservation help, there is widespread motivation on the part of the public to conserve, recover, and build resilience into populations being affected by white-nose syndrome, habitat loss and other localized threats.
Building bat houses or bat boxes can be one way to help bats, but it’s not always helpful (see our bat house question and answer page). Protecting and retaining natural roost habitats (old, mature trees and dead trees in early stages of decay) should always be the first choice for providing habitat to bats. To help bats, leave these trees in areas where they are safe and allow young trees to mature.
When building roosts are lost due to exclusion or demolition, and in urban areas where natural habitat is limiting, installing bat houses can ensure that female bats continue to find suitable places to raise young. This is the best use of bat boxes and should be the main reason for their consideration.
If you’re thinking about adding bat boxes in your yard or community, please remember to never touch or handle a bat directly. Use heavy leather work gloves when following capture guidelines. If you’ve already determined that boxes will help bats in your area, here are some pro tips to consider:
Construction materials and designs:
- Do check the quality of the design or boxes you are considering purchasing, using these tips and best management practices as a guideline. The internet is full of highly variable bat house designs that may not be appropriate or effective. Avoid single-chamber boxes and anything the size of a typical bird house, as they may heat up quickly and cool down rapidly, and large single-chamber boxes, which may not provide enough height to produce a gradient of internal temperatures nor enough mass to retain heat at night. For most situations, a multi-chamber maternity bat box that is taller than it is wide will be sufficient to provide bats with a range of microclimates.
- Do choose a house or box design that includes venting to create cool areas or escape zones, and which can withstand more frequent/extreme heatwaves (even in northern climates!)
- Do choose interior materials that are untreated and free of chemical residues, with roughened or grooved surfaces that allow bats to grip and climb. Interior roosting panels may be plywood, cedar, or recycled wood materials that are not chemically treated.
- Do avoid window screens on the inside of your chambers. Window screens can separate over time, creating spaces where guano and bats (especially pups) can become trapped. Guano accumulation can lead to increased numbers of bat parasites and increase the need for box maintenance.
- Do avoid boxes with horizontal surfaces that may retain high loads of bat guano.
- Do space your crevices as appropriate for the species you think will use the box. For little brown and Yuma myotis, that width is approximately ¾” wide, 1-1.5” for big brown bat. Varying chamber widths within and among bat boxes can increase the number of species that can use the boxes.
- Do treat the exterior with three coats of a weatherproofing sealant (flat, exterior-grade, water-based paint or stain). Exterior grade plywood and exterior materials should be at least ½” thick for durability.
- Do include a ‘landing pad’ with a rough surface that extends below the chambers, and allows bats to climb upwards from an entrance (rather than down).
- Do use weatherproof wood screws. Nails may pop as wood warps, creating unwanted ventilation and gaps through which rainwater may enter.
- Do use weatherproof caulk on seams to make sure your box is weather-tight.
- Do ensure that no sharp screw or nail ends protrude inside the structure structure
Something temporarily or permanently constructed, built, or placed; and constructed of natural or manufactured parts including, but not limited to, a building, shed, cabin, porch, bridge, walkway, stair steps, sign, landing, platform, dock, rack, fence, telecommunication device, antennae, fish cleaning table, satellite dish/mount, or well head.
Learn more about structure which could injure bats crawling or flying into the structure. - Do clean the inside of bat houses using a small brush with an extension when the bat house is unoccupied (usually winter). Do not clean the inside with water or pressure washers, which can delaminate plywood baffles and speed deterioration.
Placement considerations
- Do consider an elevated spot, so that bats can take flight with ease by dropping out of the box. The exit should be 10 to 16 feet off the ground.
- Do choose a spot that is free of vegetation immediately below or in front of the box and that will not become overgrown.
- Do avoid placements that provide easy access for predators like domestic cats, snakes, owls, raccoons, rats or other ground predators.
- Do avoid sites near toxic drinking water sources or a contaminated food supply (all structure-roosting bats in North America eat insects).
- Do avoid sites with high levels of human traffic that might draw vandals or harassment.
- Do avoid areas that are consistently cold, shady, or windy.
- Do avoid locations with abundant artificial light, air pollution (including dust or smoke) and/or noise.
- Do choose a location near other habitats that bats may use for foraging, such as forest and field edges, wetlands, and forested paths.
- Do keep rain barrels and other smooth-walled containers that may catch water covered, upside down or away from bat boxes to avoid drowning, or equip them with escape terrain such as a ramp or piece of wood bats could use to climb out if trapped.
What to watch for:
- Check your box at least once a year for any necessary routine maintenance, such as recaulking, painting, and cleaning out abandoned wasp 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.
- 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.
- Monitor your box, checking periodically for guano and bat activity. If bats are actively using your box, pay particular attention during periods of extreme heat. You may need to temporarily shade the box with an awning if you see signs of heat stress.
- Bats begin emerging just after sunset and can be easily counted while sitting nearby. Many states have volunteer programs to count and report bats.
For more information, consider these Best Management Practices for the Use of Bat Houses in the U.S. and Canada.
Here is one design that you may consider.
