Hosting a Bat House

A recent inquiry to me asked about whether or not fall is a good time to put up a bat house. The short answer is No, it's not the best time. Then again, putting up a bat house is always a good thing, though fall is not the best time.

A bat roost box, or "bat house," on your property is a good way to do local wildlife conservation. Bats are incredibly important, especially in insect (mosquito!) control. Bats - like snakes, coyotes and many insects - have a bad reputation in our culture. A single adult bat can eat close to its body weight in insects every night.

A bat roosting box helps bats to persist in the face of many significant threats, including habitat loss, mortality from wind turbines, and impacts from a fungal disease called White-Nose Syndrome. A bat "roost" is the place bats use to rest and raise their young. In their natural habitat, bats roost in tree cavities, among leaves, and under bark. 

Some species have adapted to roosting in man-made structures such as houses, barns, and bridges and these bats will occupy roost boxes. It is similar to those birds who will use artificial nest boxes. The two species that most commonly use bat houses in the northeast United States are big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus).

So, when is the best time to put up a bat roosting box? Early spring would be the best time as it is during the spring and summer months when females roost together in "maternity colonies" to raise pups. (Males may use bat houses to roost individually or in small groups.)

Bat box on Amazon.com

Bats are rather particular when it comes to finding a new home. You can purchase a bat house online or from a wildlife specialty store, or you can construct a bat house yourself. I sent the inquirer a link to Rutgers Wildlife Conservation and Management Program at  wildlife.rutgers.edu/bats/

Their website is the best place to find out the details, but here are some bat preferences for roosting: 

• box size at least 2 feet tall and 14 inches wide
• with single or multiple roosting chambers
• vents, ½ inch wide on the front of the bat house allow for airflow
• Face the bat house south/southeast to attain maximum sun exposure (6–8 hours/day). Most bats need temperatures >85°F to retain body heat and keep young pups warm. Morning sun is best.
• Mount the bat house at least 12 feet off the ground. Higher is better. Bats swoop into and out of the bat house, and they need plenty of clearance to do so.
• If possible, choose a location near a water body such as a stream, river, pond, or lake.
• Bat houses can be installed on the sides of buildings, poles, and dead trees ('snags').
• Make sure there are no artificial lights directly shining onto your bat house, and no vents blowing air at the bat house.

In the spring, bats return from hibernation to their summer roost sites, so having a box up prior to their arrival is the best time. You may not get occupants the first year. The location is critical. Farmland, woods, and water are all ideal but not absoli=ute requirements. Once found and used, bats should return yearly to the same location.

Once you have a bat house, you can join the Rutgers Bat House Distribution Program which provides and installs free bat houses to homeowners who are getting a bat exclusion performed on their property. But any homeowner can also enroll in their bat-monitoring program.