Chiroptera - The Only Mammals That Fly
Are you afraid of bats? Well, you shouldn't be. These wonderful little nocturnal creatures eat thousands of bugs each night, some of which are deadly, like mosquitoes carrying West Nile Virus. The risk of rabies is insignificant and bats don't attack people. They don't even like people and North American bats don't have any interest in drinking your blood. By improving habitat for bats and providing them with manmade roosting places, the risk of insect borne diseases is decreased and the bats are less likely to move into attics and places where their droppings could become a problem for humans.
Bat habitat is diminishing at an alarming rate. You can help by building and erecting bat houses and informing others about the benefits of these widely misunderstood nocturnal creatures. If you are interested in getting rid of bats in a home or other structure, there are ways to eradicate bats from a home or other building without harming them. It is called "exclusion" and involves giving them a way out but no way back in. Anytime you remove bats from their home or destroy their habitat, it is time to think about erecting bat houses to give them a new, safe place to live.
Many farmers have been able to stop using pesticides by creating habitat for bats around crops and animals. Another benefit of building bat houses is that they are less likely to attempt to move into human dwellings and places where they are unwanted.
The most common species found in North America are Little Brown Myotis, Free-tailed Bat, and Big Brown Bat.
Building the Perfect Bat House
Bat houses should be at least two feet tall and open on bottom, with a landing zone extending at least six inches below the rear panel. The ideal inside dimensions are 25" or more in height and 20" or more in width. Virtually any size will work that provides darkness, ventilation, and protection from the elements, but bigger is better, slightly taller than wide.
Roosting partitions must be 3/4" to 1' apart. The 3/4" spacing is ideal for North American bats and aids in keeping out predators and wasps. One or two crevices is acceptable but more is better. Five or more roosting spaces are best.
Internal surfaces and landing areas should be very rough or grooved horizontally. If your wood is very flat, you can groove each piece of wood with a circular saw. Another option is to scratch the surfaces deeply with a sharp nail or screw. However you choose to roughen the interior surfaces, just keep in mind that the bats and their young have to hang on to these surfaces all day long. The landing surfaces can be roughened in the same manner or covered with plastic mesh like the bat mesh available from Internet Inc. Be careful not to leave any sharp edges.
Bat houses should be vented if summer temperature is above 85 degrees. The side vents should be approximately 3/8" by three to six inches, aligned vertically with the back panel, starting about one third up from the bottom of the roosting chamber. The front vent should be 3/8" tall and run across the width of the bat house, also up one third from the bottom of the roosting house. If the bottom of the side vents is aligned with the front vent, fresh air will come in through the front, move around the top of the roosting chamber, and out through the side vents. The top of the inside partitions should be at least 1/2" below the inside of the roof for air flow.
Exterior plywood or non-aromatic Cedar is best for building bat houses. Plywood with a strong chemical odor or Cedar that smells very strong should be avoided. Plywood does not have to be very thick, as long as the finished house is sturdy and robust. If thicker wood is used, a multi-chamber house can get very heavy. There is no need for interior partitions to be thicker than 3/8" but 1/2" to 3/4" will work better for the exterior panels. Assembly should be done with coarse, rust resistant, drywall screws and all joints should be caulked. When weatherproofing, keep in mind you do not want to have to take a bat house down for maintenance very often, so do it right the first time. If you do need to remove a bat house for cleaning or repairs, do it in the coldest part of winter when bats have most likely moved to caves for hibernation and wasp are likely to be gone. Bats have been known to stay in manmade bat houses year round in Southern California and other locations with very mild winters.
Bat houses should be protected from sun and moisture with several coats of exterior grade latex paint. The inside surfaces should not be painted but can be darkened with water-based stain. It is important to avoid strong odors when choosing paint and stain so look for products that are labeled low-toxicity or non-toxic. The exterior color should be selected according to your geographic region. Darker colors, even black, can be used in the north, but in the deep South, lighter colors should be used to prevent overheating in direct sun. Southern California and Gulf Coast bat houses should be white or very light colors and throughout the middle United States , any medium color should work. The roof can be covered with tin or asphalt type roofing material for extra long life.
Bats are warm blooded mammals just like humans, so temperature control is an important consideration when choosing a location. Full sun is preferred in the North and at least partial sun, preferably in the morning, in the South. The front of the bat house should always face southeast to take advantage of the warm morning sun and reduce heat in the late evening. It works well to have two bat houses on one pole, mounted back-to-back. The more houses you have, the better chances of success, since the bats will have more options in finding a crevice that suits them.
Bats will fly many miles to feed but it is best to be within 1500 feet of water whenever possible. Houses should be mounted on poles or structures, not trees, at least twelve feet above ground. Twenty feet or higher is best. There should be no obstacles, including tree limbs, within fifteen feet of the pole or structure where the house is mounted.
Care should be taken to eliminate the possibility of predators reaching bat houses. During the winter, wasp nests can be removed. If the bat house cannot be lowered to the ground, use a long cane pole of something similar to remove the nest. DO NOT attempt to remove wasps if bats are present!
If you are planning to evict bats from a building, put up a bat house several weeks prior. This will ensure that paint and caulking has completely dried and offensive odors are gone. Hang fine screen mesh or fabric over the point where bats are entering a building leaving it open only at the bottom. The bats will find their way out but will not be able to get back in. There is no need to kill or poison the bats to evict them from a building, just exclude them and give them a new home. It is not required that you have a bat house available to carry out an eviction, but it will help deter them from moving into your neighbors home.
Do not handle or breathe bat droppings. Although it makes good fertilizer, there is a mold that grows on the guano that is toxic to humans.
Do not handle bats unless you are a professional and take proper precautions. North American bats rarely come near people and are of little danger when left alone. Although the risk of rabies is low, it should not be ignored. The CDC has some good information on bats and rabies.
Bat Links
Bat Conservation International
Organization for Bat Conservation
Bat Conservation and Management Inc.
Disclaimer - I make no warranty regarding the above information. I am not a biologist. I have studied bats casually and put into my own words what I believe to be the best practices for improving bats habitat.