Big brown bats (Eptesicus fuscus) are found almost everywhere in the contiguous 48 states and southern Canada, and south to Colombia and Venezuela. Their appetite for cucumber beetles, stinkbugs, June bugs and leafhoppers makes them one of the farmer's and gardener's most valuable allies.
This species is one of the top three bat-house users in North America. Volunteers in BCI's Bat House Project have attracted them to farms, suburban backyards and parks. Big browns are cold hardy and have overwintered in bat houses as far north as New York. In summer, however, these bats prefer roost temperatures below 95 degrees F (35 degrees C), a bit cooler than other common bat-house tenants, such as little brown myotis (Myotis lucifugus) and Mexican free-tailed bats (Tadarida brasiliensis), will tolerate. Big brown bats often roost in the coolest part of a bat house (the back chambers, for instance).
Our volunteers' experience with big browns has produced a great deal of data and tips for attracting these beneficial bug-eaters to your bat house.
North of Sacramento, California, 170 big brown bats live from May to December in two nursery houses mounted on a building. These houses are painted black, face west and receive seven hours of daily sun. This setup would normally be too hot for the species, but the elevation is 2,700 feet (823 meters) and the average July high temperature is only 87 degrees F (30.5 degrees C).
More than 1,200 big brown bats stay year-round in about 20 bat houses at two locations in northeast Texas. Most use insulated houses that receive full sun. The two largest known colonies of big browns in bat houses - about 500 each - raise their young and overwinter in two houses, each four feet (1.2 meters) wide by 27 inches (68 centimeters) high.
About 90 big browns at Devil's Den State Park in Arkansas move among 10 houses from March to October, and about 30 bats at Lake of the Ozarks State Park in Missouri move among four houses year-round. At both parks bats switch from sunny to fully shaded houses, according to changes in the weather.
In the suburbs of Tampa, Florida, 100 big brown bats beat the heat year-round in a north-facing, medium-brown bat house on a pole, whereas in southern New Hampshire, a summer colony of 100 stays warm in a southeast-facing, dark-red box on a stone building.
This species relies almost exclusively on human-made structures for summer roosts, as they have lost much of their natural habitat. They travel short distances to feed, usually less than 1.2 miles (2 kilometers) from their roosts. So you'll enjoy the insect-hunting benefits of any big brown bats that move into your bat house.
For more information on bat houses and attracting bats to them, visit the Bat House Project online at www.batcon.org/bhra .
