Homeowners and Bats
Information and Tips for Dealing with New Hampshire Bats
Bats in Your House
If bats fly into the living spaces of your house, don’t panic. They do not want to be there. Open any outside windows and doors to the room where the bat is, and leave the room, closing any interior doors behind you and turning off the lights. They will soon find their way outdoors.
If you have them trapped already, you can let them go outside. In the summer, let them go as soon as possible. In the winter, choose the warmest part of the day for release. Bats found in buildings during the winter may not survive if released outside in below-freezing temperatures, high winds, or heavy rain. If you find a bat in any of these conditions, contact a licensed wildlife rehabilitator.
Do not touch a bat with your bare hands. If you touch a bat, you may be exposed to rabies. Call your doctor and the NH Department of Health and Human Services, Bureau of Infectious Disease Control, at (603) 271-4496 right away. See below for more information about bats and rabies.
Bats in Your Attic
Bats like to roost in attics because they are hot, safe places to raise their young, called pups. Big brown bats may also use buildings for hibernation in the winter. Bats may have pups from mid-May to mid-August. The pups will begin to fly in July, but still need a safe place to roost for a few weeks.
If you seal up your attic before the pups are ready to leave, they either will be trapped and die, or will find their way into the living spaces in your house. The mother bats may also fly into your home, seeking a way back to their pups.
In mid-August, the bats generally leave to seek a safe place to spend the winter, so this is a good time to exclude bats.
During July, you can figure out how bats are getting into your attic. Observe where the bats exit at dusk so you will know which holes you need to seal.
Then in August, when the bats are ready to leave, you may bat proof your structure through exclusion. It is a safe, effective, and humane way of evicting unwanted bats. Use one-way doors to make sure the bats are out before you seal. You can either do this yourself or hire a licensed Wildlife Control Operator by clicking this link, you will leave the Fish and Game website in New Hampshire. To create a one-way door, hang screening material over the remaining openings; the piece of screen should be tacked down at the top and sides, but left open at the bottom to allow the bats to crawl down the wall to fly away. They will not be able to figure out how to crawl back up to re-enter.
Avoid removing bats from mid-May through mid-August.
Why are Maternity Colonies in Barns and Houses Important?
Bats breed very slowly. Most bats only have one pup a year, and of course many do not make it through their first year. Since so many bats are dying of white-nose syndrome, it will take decades for the bat population to recover.
Two bats prefer buildings for their maternity colonies, little brown bats and big brown bats. They breed more successfully if they are crowded together in a hot place. High heat allow the pups to spend all their food energy on growth, and not on staying warm. The large number of bats protects them too. Mother and baby bats find each other by recognizing each other’s calls.
Bat Houses
Bat houses are substitutes for buildings, but in general are not as good a colony location due to their smaller size. However, they can be helpful to bats, and support maternity colonies if designed correctly and put in the right place.
First, you must get the right sized house. Research by Bat Conservation International has shown that the house is much more successful if it is at least 25 inches tall. Location is also key. Put the house on a building or pole so that bats can easily find it. Remember that they are looking for buildings to roost in, so are more likely to find one on the side of a building. Put it near the roof if possible - at least 12 feet off the ground. Since bats, particularly females, like high temperatures (80-100°) the box should be on the southeast to south side of the building, and exposed to lots of sun. The exterior of the box should be dark to absorb more heat. Remember that guano will fall out of the box, so don’t put it above a door or deck.
Maintain your box. Clean out wasp nests in winter, and check to see that the caulking is still functioning.
Bat house plans can be found on many websites. Start with Bat Conservation International (www.batcon.org) to see more details of the best houses, then find the plan or already built house that suits you.
Guano
Bat guano accumulates under bat colonies. This can be a problem in barns and other outbuildings where equipment is stored. To protect your bats and your stuff, consider creating a ceiling between the roof and your stuff. One barn owner has rigged up a tarp flat above his tractor. The tarp catches the guano from the bats. The tarp is held up with ropes that allow the tarp to be lowered back down to the floor, but remain flat while doing so. This means the tarp can be cleaned off periodically.
Large accumulations of bat guano may harbor histoplasmosis fungi spores, which when inhaled can result in a lung infection referred to as histoplasmosis. In the United States the fungus mainly lives in soil in the central and eastern states, particularly areas around the Ohio and Mississippi River Valleys. Precautions, such as wearing a respirator, should be followed when cleaning or removing large accumulations of bat guano. For more information, see the U.S. Centers for Disease Control and Prevention website on Histoplasmosis.
Rabies and Bats
Bats can carry rabies, so it is important not to handle bats with your bare hands. Not many bats have rabies, but it is best to be cautious. Bats in your house would prefer to fly out, so open any outside windows and doors to the room where the bat is, and leave the room, closing any interior doors behind you and turning off the lights.
If you handle a bat with bare hands, or if a bat is found flying in a room with a sleeping child, you should call your doctor and the NH Department of Health and Human Services, Bureau of Infectious Disease Control at (603) 271-4496 right away. Do not release the bat as it can be tested for rabies if you have it.
For more information on rabies see the NH Department of Health and Human Services website.
Bats Flying in the Winter
Bats have two strategies to survive the winter. Three of our bat species fly south. Five of our bats hibernate, mostly in caves and mines. One, the big brown bat, also hibernates in buildings. People sometimes see big brown bats flying outside on warm days, looking for a quick snack. If you see bats flying in a neighborhood or other developed area, they are likely big brown bats.
Some bats flying outside may be a victim of white-nose syndrome, a new disease that is affecting bats as they hibernate in caves and mines. A white fuzzy fungus grows on their faces, wings and tail, and caused them to wake up from hibernation more often than they would normally during the winter. They use up their stored fat much more quickly and become emaciated. Some fly out of the hibernacula in search of food, but are doomed.
As early as late March, some bats may decide to emerge from hibernacula to seek food, but most wait until mid-April.
For more information on bats in New Hampshire, contact the Wildlife Division at wildlife@wildlife.nh.gov