A Homeowner's Guide to Bat Proofing

Bats in the House

Although approximately 40 bat species live in the United States, only a few are dependent on buildings for roosting. These bats once roosted in hollow trees until early settlers eliminated large expanses of forests. Whether living in a tree or a building, bats are loyal to their roosting sites. If the bats leave for part of the year, they will return annually to the same roost as long as the site remains available to them.

 

In many buildings, there is little chance for contact between people and bats, thus there may be no reason to evict them. Because these beneficial animals have only one or two pups a year, the protection of their maternity colonies is important to their survival. Therefore, extermination of any colony should be avoided. The only safe eviction method, for both bats and humans, is a three-step procedure called bat-proofing.

Bat-proofing Materninty Colonies

Step 1 - Providing an Alternate Roost
Bats evicted from their roost may move into someone else's home where they risk being exterminated. Furthermore, colonies with babies will not allow newcomers. If a displaced colony cannot find a new home, they may leave the area resulting in a decline of local bat populations. Well-placed bat boxes provide bats sanctuary outside of the home, while the homeowner still benefits from the bats' control of insects.

 

Bat boxes should be placed on or very near the building in which bats roost. This can be next to the current roost site, on the chimney, or on a wooden pole within 10-20 feet from the roost. When placing a bat box on the chimney, allow at least 3 feet of open space between the box and roof. When placing the box on a pole, the box should be at least 10-15 feet above the ground.

 

Bat boxes should be at least 7 inches deep, 25 inches wide, and either 12 or 24 inches tall. Baffles divide the interior of the box into crevices which measure from 3/4 inch to 1 inch wide. Baffles and interior surfaces should be roughened with saw cuts, or covered with plastic mesh to provide bats with footholds. Position bat boxes so they receive the first 7 hours of morning sunlight. Paint boxes dark brown to absorb more heat from the sun. However, avoid positioning boxes where they will overheat in the afternoon sun. With a bat box in place, the exclusion of bats from the building can begin, and the bats will have time to become familiar with their new roost.

 

Step 2 - Fashioning an Exclusion Device
Homeowners who wish to bat-proof their homes should begin by locating the bats' exit points. This must be done at dusk while the bats are emerging.

Exclusion devices are handmade, one-way valves. Excluders can be made from clear plastic sheeting, fiberglass screen, or bird netting. Cut enough material to cover the entire emergence area, and extend approximately 2 feet below it (FIG.1).

Figure 1 - Correct installation of handmade bat excluder

 

With strong tape or staples, secure the cut piece of sheeting to the building along the top and side edges. Leave the bottom edge open for the bats to escape (FIG. 1). The sheeting should be loose enough to slide a hand under the bottom. When properly installed, the sheeting allows bats to escape easily out the bottom, but when they return to roost, they are unable to find the entrance. Not all bats leave their roost every night. To ensure that all bats have left, leave the exclusion device in place for at least 3-4 days in warm weather, and longer in cool or cold weather: bats do not hunt when temperatures are below 60-65 degrees Fahrenheit. Because bats are active at dawn and dust, excluders should be installed during late morning to middle afternoon. If this simple rule is followed, it is unlikely that bats will attempt to leave the roost while an excluder is being placed. Examine the rest of the dwelling, inside and outside, for holes that might allow bats entry. Entry points larger than 1/4 inch by 1/2 inch should be caulked. Windows should be screened, chimneys capped, draft-guards placed under doors leading to the attic and outdoors, and plumbing fixture holes should be filled with steel wool or caulk.

 

Step 3 - Sealing the Roost
After all bats have left, permanently seal roost entrances. Before removing the exclusion device, cut a section of 1/4-inch hardware cloth large enough to cover the area. Remove the excluder and attach the hardware cloth with strong staples. (FIG. 2) depicts a permanently sealed roost.

Figure 2 - Permanently sealed entrace using 1/3 inch hardware cloth

Removing a Single Bat

Occasionally, a single bat will enter a homeowner's living quarters. If this occurs, confine the bat to the room in which it was observed. Allow the bat to fly without intervention. Never try to catch a flying bat. When the bat tires, it will come to rest on a curtain, piece of furniture, or wall of the room. Allow it to rest for approximately 30 minutes. During this time the bat's body temperature will drop to the temperature of the room. The bat enters a state of inactivity called torpor. Typically, a torpid bat does not fly. To capture and remove it, follow these simple steps:

1. Put on a pair of leather gloves.
2. Place a plastic bowl or coffee can over the bat while it is resting. If the bat flies, allow it to stop and rest again before removing it.

3. Slide a piece of rigid cardboard between the container and the bat's perch, trapping the bat inside the container (FIG. 3).

Figure 3 - Safe method to capture a bat

4. Release the bat outdoors in a place away from animals that will prey on it. The bat may not fly away immediately. If it is still present the following day, call your local wildlife agency.
5. If a bat bite is suspected, keep the bat and call the local health authorities to test it for rabies.
6. If recurring problems with bats entering the home occur, inspect the home for a colony of bats.

 

A WORD OF CAUTION
During spring and summer, young bats are unable to fly. If their mothers are evicted during this time, the young will be trapped inside the building. Besides the obvious odor problems from dead pups, those that survive may enter human living quarters in search of a way out. Females may frantically attempt to re-enter the building, even during daylight hours, to rejoin their young.
Avoid bat-proofing from May through August.