Bat house construction and installation can be an environmentally friendly and rewarding activity. Putting up a bat house, however, does not guarantee that bats will use it. We don‘t know exactly why bats dwell in one house and not another, but by following a few recommendations you can increase the likelihood that bats will live in your bat house.
Stephen Vantassel Project Coordinator—Wildlife Damage
Scott Hygnstrom, Extension Specialist—Wildlife Damage
Ron Johnson, Extension Specialist—Wildlife
Dennis Ferraro, Extension Educator—Douglas-Sarpy County
Some bats live in colonies that include tens of thousands of individuals. In Nebraska, the big brown bat (Eptesicus fuscus) and little brown bat (Myotis lucifugus) live in colonies of 10 to 200 and are the most likely candidates to occupy your bat house. Both species frequently occupy attics, belfries, barns, and other structures.
Generally, bat houses should be placed in rural locations such as on farms, acreages, or natural areas where other habitat needs are present. Bat houses will more likely be occupied when they are installed in areas where bats already exist. Several approaches can be used to determine if bats occur in your area: 1) observe outdoor lamps at night to see if bats are feeding on the insects that have gathered there, 2) ask friends and neighbors, your local extension educator, or wildlife officials about their knowledge of bats in the area, or 3) try using a bat detector, a device that can detect ultrasonic bat sounds. Even if bats don’t live in your area, you may be able to attract them by installing bat houses. Since bats consume a significant amount of energy when flying, they are more likely to live in a structure close to food and water. Place bat houses within 1/4 mile of standing water, such as a stream or pond that will provide bats with water and habitat for their prey, namely insects. Areas prone to insecticide use may not be as successful as locations where insecticide use is limited.
Install bat houses to ensure that they are exposed to sunlight for more than seven hours per day, which will typically require the house to be placed on the south, southeast, or southwest side of a building. Bats are more likely to occupy bat houses installed at least 12 feet above the ground and with at least 20-30 feet of clear flight space around the bat house. It doesn’t seem to matter whether bat houses are installed against buildings or on poles, provided adequate sunlight is available. Cover the exterior of the house, or the exterior top half, with dark or medium shades of water-based, exterior-grade paint or stain, or tar paper to increase the house’s ability to trap radiant energy. While male bats will occupy cooler houses, females need the heat provided by sunlight to maintain warm nurseries for their pups. Place several bat houses in a variety of areas, such as all four sides of an infrequently used barn to increase the likelihood of occupancy. Avoid placing bat houses on tree trunks, as shade will reduce the house’s exposure to sunlight and increase vulnerability to climbing predators, such as raccoons and house cats.
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Install bat houses only in isolated areas. |
Bat house design is also an important consideration to increase bat occupancy. In general, bats prefer larger bat houses over smaller ones. Bat houses should be at least 24 inches tall x 16 inches wide x 4 inches deep (1,536 cubic inches) [see bat house design]. Houses should be multi-chambered and approximately 1/3 taller than wide to provide space for bats to move up and down as temperatures inside the bat house fluctuate. The wood should be rough cut or have 1/8-inch horizontal grooves cut along its vertical length at 1/4- to 1/2-inch increments to provide bats with footholds. The wood should be free of arsenic based wood preservatives. Caulk any gaps and crevices along seams to eliminate drafts and keep the inside of the house at the preferred temperature. Never paint the interior of the house. The roof should be watertight and able to shed water easily.
Some bat enthusiasts smear bat droppings, called “guano,” on the interior of bat houses or place droppings on the ground underneath to attract bats. It is unclear as to whether or not the presence of bat guano increases the likelihood of a bat house becoming occupied.
If bats are being evicted from a building, bat houses could be installed to provide them with replacement housing. Evicted bats may move into nearby bat houses.
Avoid using insecticides or other pesticides around bat houses. Wasp nests can be removed, at night, with a long pole, provided bats are not present. Bat houses should be inspected and repaired each time the colony leaves for the winter. Pay special attention to the house’s seams, roof, and structural integrity. Make repairs as needed.
Biologists discovered that bats frequently took up residence beneath corrugated aluminum sheets installed around trees to protect wood duck-nest boxes from raccoon predation. You can construct this alternative bat shelter using aluminum sheets, tar paper, or similar material around tree trunks or poles. The sheets were 20-90 inches wide and secured to the tree-trunks so that the bottom edge stood 2 to 4 feet above the water line. To make one, find a suitable tree or pole in the middle of a pond or lake. These are ideal, as they receive ample sunlight and are close to much needed water. Trees at field edges or in windbreaks may also work, provided there is sufficient sunlight. Wrap the pole or tree with the bottom of the sheet at least 3 feet above the water line or 12 feet above the ground surface. Place the sheet higher on the pole or tree, if possible, to give the bats more room to gain altitude to fly. Secure the entire top edge of the sheet tightly to the tree or pole with aluminum nails to keep out rain. Leave the bottom of the sheet open to allow the bats free access and for the guano to fall out. Ideally, the bottom should flare out about 1/2-1 inch, at the narrowest point, from the pole or tree. Check the sheeting in the off-season to ensure the top is secure and that guano has not clogged the bottom in order to maintain the site’s suitability for bat occupancy.
Bats that live in Nebraska eat only insects. Their diet includes a wide variety of flying insects, including many that are annoying to people or damage gardens or agricultural crops. Where bat numbers are sufficient, their foraging may be a significant factor in reducing populations of insect pests. Further, some insects are deterred by bat echolocation, the mechanism that bats use to locate prey. At least one study reported that batlike sounds over corn deterred moths and reduced damage by corn borer larvae. It is unreasonable, however, to expect bats to eliminate all flying insects that might be considered a problem.
Educators and youth workers might consider bat house construction as a fun activity for young people, with the educational and conservation values gained by helping bats as foremost goals. Bat house construction is just another way that humans can co-exist with wildlife in a mutually beneficial manner.
Bats also present potential dangers. Bat houses increase the likelihood of human-bat encounters. Flightless pups occasionally fall out of bat houses within easy reach of children and pets. Although rare, such encounters can result in bites and exposure to rabies. Risk can be reduced by teaching children to never handle bats and by keeping the vaccinations of pets current. Place fencing or ornamental plantings around the base of the bat house mounting pole or site to minimize access to pups if they should fall out and to reduce disturbance to the colony. Bat bites are extremely difficult to see on skin. If there is any possibility that a person or animal was bitten by a bat, seek medical attention immediately. If the bat is still present and not flying when the suspected bite occurs, capture the bat without handling it so that it can be tested for rabies. A downed bat can be captured by sweeping it into a bucket or similar container or by throwing a heavy cloth such as a towel over it and gently rolling it into the cloth or towel. Wear thick gloves to protect your hands.
Bat droppings inside caves, buildings, or structures can encourage the growth of fungal spores that can cause histoplasmosis. This fungal disease is typically found in more eastern and southern parts of the U.S. where the climate is hotter and more humid. This fungus occurs naturally in the environment and can become more concentrated, and therefore more infectious, when piles of guano are present inside caves or structures. Avoid disturbing the guano or performing any activity around the bat guano that might cause the spores to become airborne. If guano is present inside a structure and needs to be removed, read the suggestions found in the Bat NebGuide (insert number ) http://ianrpubs.unl.edu/wildlife/ and at the Centers for Disease Control http://www.cdc.gov.
Bat guano makes an excellent fertilizer. It must be used with care, however, as it contains enough nitrogen that it could “burn” your plants.
Bat Conservation International (www.batcon.org) and their bat house research project (www.batcon.org/bhra/) have regularly-updated and reliable information on bat conservation and bat houses.
Belton, P., and H. R. Kempster. 1962. A field test on the use of sound to repel the European corn borer. Entomologia experimentalis et applicata 5:281-288.
Freeman, P. W. 1983. Bats, winged Maestros of the night. University of Nebraska State Museum & Planetarium, Museum Notes 71 (4 pages).
Kiser, Mark. 2000. Pole-Mounting Tips. The Bat House Researcher. Vol 8 , No 2:4-5
Tuttle, M. D. 1988. America’s Neighborhood Bats. University of Texas Press, Austin.
Tuttle, M. D., M. Kiser, and S. Kiser. 2004. The Bat House Builder’s Handbook. University of Texas Press, Austin, 35 pp.
Whitaker, J. O., Jr. 1995. Food of the big brown bat, Eptesicus fuscus, from maternity colonies in Indiana and Illinois. American Midland Naturalist 134:346-360.
Williams-Whitmer, L. M., and M. C. Brittingham. 1995. A homeowner’s guide to northeastern bats and bat problems. Pennsylvania State University, University Park, PA (23 pages).
For more information on bats, see the Bat NebGuide (insert number) ianrpubs.unl.edu/wildlife/
Internet Center for Wildlife Damage Management icwdm.org is a collaborative effort by the University of Nebraska–Lincoln, Clemson University, Cornell University and Utah State University dedicated to provide research based information on all aspects of wildlife damage management.
Special thanks to Bat Conservation International www.batcon.org/ for permission to reprint their bat house construction guidelines. Building instructions for the more advanced “Rocket Box” Bat House can be obtained at icwdm.org
This publication has been peer reviewed.
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