Homeowners and Bats

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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 you can. In the winter, choose the warmest part of the day for this if you can.

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 Department of Health and Human Services at (603) 271-4496 right away. See below for more information about bats and rabies.

In the winter, big brown bats may show up in your basement, as that is a common access point. This is the only species that regularly uses buildings for hibernation. <back to top of page>

Bats in your attic

bat exclusion
Illustration of a "bat exclusion." The bat can crawl down and fly but will not figure out how to get back in.

Bats like to roost in attics because they are hot, safe places to raise their young, called pups. 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 seal up your attic.

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 go, the openings can be permanently sealed. 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. If there are multiple holes, you might want to seal up some first. 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 (see illustration). They will not be able to figure out how to crawl back up to re-enter.

To recap, avoid removing bats from mid-May through mid-August. Be aware that, to help protect bats, a 2012 rule prohibits the exclusion of bats from unoccupied structures by licensed Wildlife Control Operators from May 15 through August 15, unless the N.H. Department of Health and Human Services has documented a rabid bat on the property. 

Once the bats are gone, see below for advice on removing the guano. <back to top of page>

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. <back to top of page>

Bat Houses

bat house
Bat house on the outside of a NH barn. Photo courtesy of P&S Country Crafts L.L.C.

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 15 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. <back to top of page>

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 and the accumulated guano used in the gardens as a great fertilizer.

When handling large amounts of guano, such as when cleaning off these tarps, wear gloves and a mask to protect yourself. If the guano has accumulated for a while, it can grow a fungus called Histoplasma capsulatum, which causes a disease called histoplasmosis. This is a respiratory disease. Wear a respirator if you are cleaning up large amounts of bat guano. This disease also occurs in accumulated bird droppings, such as in poultry houses. <back to top of page>

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 Department of Health and Human Services at (603) 271-4496 right away. Do not release the bat as it can be tested for rabies if you have it. Rabies is a fatal disease – but it is treatable if you do so immediately.

For more information on rabies see the Department of Heath and Human Services Communicable Disease Control & Surveillance webpage at dhhs.nh.gov/dphs/cdcs/rabies.

Download a NH Fish and Game pamphlet on wildlife-related diseases - click here (PDF).

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 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. Click here for more information about white-nose syndrome.

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.

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NH Fish and Game Dept.
11 Hazen Drive
Concord, NH 03301

603-271-3421
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