November 16, 2018
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How to set up a bat house

Courtesy of Bangor Land Trust
Courtesy of Bangor Land Trust
Large bat houses built by Bill Childs are erected on July 30, 2015, in West Penjajawoc Grasslands, a Bangor Land Trust property in Bangor.

As symbols of Halloween and all things spooky, bats have a bad reputation. In films, they’re ever present in graveyards and haunted mansions. In folktales, they’re manifestations of vampires, out to suck your blood. And in everyday life, they’re often seen as dangerous pests. But in recent years, conservationists have have devoted more resources to educating the public about the benefits of bats and how they play a crucial role in the environment.

As a result, some people are adding bat houses to their properties in hope of attracting bats and offering them a place to roost and raise their young.

“Bat houses are definitely becoming more popular,” said Doug Hitchcox, staff naturalist for the Maine Audubon, an organization that sells bat houses at its nature centers throughout the state and has hosted several public presentations on bat conservation in recent years.

Bat houses are essentially wooden boxes filled with narrow chambers where bats can rest, conserve energy and stay warm during the day. At night, they emerge to hunt, with the majority of the world’s bats feeding on vast quantities of insects. Other bat species eat fruit, pollinating plants and distributing seeds in the process.

Bat houses are also a place where bats can give birth and raise their pups in the spring and early summer. The shelter serves as protection and as a place where bats can gather and form a cohesive colony.

Where to put a bat house

In the United States, one of the top authorities about bat houses is Bat Conservation International, an organization devoted to the protection of the world’s 1,300-plus species of bats. This organization conducted a 10-year Bat House Research Project, enlisting volunteers to research hundreds of bat houses and other artificial roosts.

From this research, BCI learned that the best location for a bat house is on the side of a building, believe it or not. People are often worried this will encourage bats to invade the building. To address that concern, BCI states on its website that “if bats were attracted to your attic or wall spaces and could get into them, they probably would already be living there.”

The best way to keep bats out of your home is by keeping the exterior of your house in good repair. Bats can enter spaces that are as small as a half-inch in diameter.

If you are successful in having bats move into your bat house, expect plenty of droppings — also known as guano — to fall from the bat house and accumulate underneath. For that reason, you’ll want to put the bat house in a place where you don’t mind there being a bit of a mess below. Perhaps a shed, outbuilding or barn. And for whatever reason, BCI found that bats prefer bat houses that are mounted on buildings with wood, brick or stone siding but not metal siding.

Courtesy of Bangor Land Trust
Courtesy of Bangor Land Trust
Large bat houses built by Bill Childs are erected on July 30, 2015 in West Penjajawoc Grasslands, a Bangor Land Trust property in Bangor.

Bat houses can also be mounted on poles. You could even fasten two bat houses together, one on each side of the pole.

Whatever you decide, make sure the bat house is located in an area with plenty of sun for heat. Ideally, they should be exposed to sunlight for 6 to 8 hours daily, so facing them to the south is a good idea. At a minimum, they should be placed 10 feet off the ground, though 12 to 20 feet is ideal. And they should be located at least 20 feet away from the nearest tree branches or other places where flying predators can perch.

“A lot of people try to put [bat houses] in trees, and that can be problematic,” Fran Hutchins, Bat Conservation International’s Director of Bracken Cave Preserve in Texas. “It makes them easy access to predators such as rat snakes and owls.”

Trees also tend to be too shady.

How to attract bats to a bat house

There’s no scent or item you can place in or around your bat houses to attract occupants, according to BCI. When bats are looking for a nice home, they consider three things: design, temperature and location.

Starting with design — not all bat houses are created equally. For this reason, Bat Conservation International provides detailed directions for the construction of three effective bat house designs. These designs were developed from BCI’s Bat House Research Project (1993-2004), during which volunteers conducted research on hundreds of bat houses and other artificial roosts.

BCI also provides links to premade bat houses and bat house kits that they consider to be adequate designs.

Many bat houses on the market are too small, Hutchins said, and the chambers inside them are often improperly spaced, allowing for too much air flow and heat loss.

“One of the general rules is the bigger, the better,” Doug Hitchcox, staff naturalist for the Maine Audubon, said. “As colonial species, they like to be together, especially when raising their pups. They want as many bats in that area as possible.”

“You want them to be large enough to hold enough bats to stay warm,” Hutchins said.

“The hotter the roost, the less energy they have to spend warming themselves.”

Courtesy of Bill Childs
Courtesy of Bill Childs
Pieces of a bat house designed by Bat Conservation International are ready to be assembled at the Bangor home of Bill and Kathy Childs recently. Bill Childs agreed to construct the bat houses as a volunteer project for the Bangor Land Trust, to be erected in the BLT West Penjajawoc Preserve.

In cold climates, bat houses will often be painted black (using outdoor, nontoxic, water-based latex paint) so they absorb more heat during the day.

And last of all — location. BCI found that bat houses have a better chance of attracting bats if they’re located near large water sources. This is because most bats species feed on insects, many of which breed in water.

Also, bat houses tend to be more successful if they’re away from bright lights. And if bat colonies are already established in nearby buildings or under bridges, bat houses are much more likely to become occupied. In the same vein, if the bat house is located near a cave or mine that serves as a hibernacula, a place for bats to hibernate, they’re more likely to become occupied.

Why bat houses matter

In the United States, one reason bat houses may be gaining popularity is because of white-nose syndrome, a disease that was first discovered in the country in 2006 and has since decimated certain bat populations, killing millions of bats across North America. This wildlife disaster has heightened many people’s awareness of the importance of bats, and has some people searching for ways to help.

“Because of white-nose syndrome, a lot of the natural roosts are getting contaminated,” Hutchins said. “[Providing] any additional habitat is helpful.”

White-nose syndrome is caused by a specific fungus that can be passed from bat-to-bat and picked up from the environment — chiefly caves where bats hibernate. In addition, different species of bats are losing habitat due the closure of old mines and deforestation, Hutchins said.

“One thing that’s missing for bats are dead trees on the landscape,” Hitchcox said. “It’s those big, dead trees that maybe get hollowed out or have loose bark that maybe they’d want to squeeze underneath, that’s what we’re essentially replicating by putting up a bat house. It’s the same reason people put up birdhouses for swallows and bluebirds. So we’re always trying to convince people that what otherwise might look like an ugly tree is actually an important piece of habitat.”

Both tree roosting bats an cave-dwelling bats with roost in bat houses, Hutchins said.

Be patient

Hitchcox said he often hears from people who put bat houses up, get discouraged when they don’t see bats move in right away, then take them down. His suggestion is to be patient. From his experience, bats can take a while to locate and move into a new bat house.

“Bird houses tend to be filled up within a week of you putting them up, but bats — for whatever reason — they’re just a little more picky,” he said. “It might take a couple of years before you start noticing bats in it.”

It’s also important to note that in colder climates, such as the Northeast, bats only use bat houses during the summer to roost and raise their young. In the winter, they move out and either migrate or search for somewhere warmer to hibernate.

“So it’s one of those situations where [if you] build it, and they’ll eventually come,” Hutchins said.

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