Bat houses can help bat populations recover

The bat population has decreased dramatically since white nose syndrome started killing the world’s
A bat box at Shaver's Creek Environmental Center, Penn State University.
A bat box at Shaver's Creek Environmental Center, Penn State University.

The bat population has decreased dramatically since white nose syndrome started killing the world’s only flying mammals almost a decade ago, but experts now see signs of a comeback and say homeowners can help it along.

A biologist who has studied the decline in Vermont’s bat population has predicted that the worst of the epidemic is over and that at least one species is beginning to recover, according to an Associated Press article published in March.

Slight signs of improvement are also being seen in New York state, says bat expert Paul Curtis, an associate professor and extension wildlife specialist at Cornell University.

Curtis and his colleagues have studied maternity colony counts during the summer breeding season for the last three years. He said the decline in colony size has been dramatic over the past decade, but the bats appear to be adapting by moving their diminished colonies to smaller spaces where they can keep warm — something essential for their young.

“We’ve seen a trend for them shifting away from the large roost sites to the bat boxes, so that’s probably the most eco-friendly thing a homeowner can do, is properly build and construct a bat box that might house animals so that they can maintain that body temperature during summer,” he said.

Although they often get a bad rap thanks to Halloween stories and their association with rabies, bats actually make great neighbors, said Curtis.

“Bats can live in close proximity to people without ever really causing any conflicts. They forage at night, they eat 100 percent insects and they rarely come into contact with people,” he said.

According to the Centers for Disease Control and Prevention, most bats don’t have rabies.

The only major predator of night flying insects, bats can put a serious dent in the mosquito population. According to Penn State Extension, a single bat can consume as many as 500 insects in one hour, or nearly 3,000 insects every night. A colony of just 100 little brown bats, the most abundant species in the Northeast, can consume more than a quarter of a million mosquitoes and other small insects each night.

Bats look for roosting spots that heat up to well over 110 degrees Fahrenheit because their young, which are born with no fur, need to devote all of their energy to growth — rather than to keeping warm — so that they will be able to fly by August, Curtis said. That’s why bats often wind up in the attics of old homes, where temperatures soar in summer. Providing a suitable substitute can keep the animals out of humans’ living spaces and help ensure young bats will thrive.

“I think people really need to pay attention and conserve bats as much as possible now, given the population decline. If we can get bats out of homes and out of living spaces and get them into bat boxes so that people can tolerate them, I think that’s a start for the population recovery,” Curtis said.

Bat boxes don’t need to be huge to hold a lot of bats. One that’s 3 feet wide and 4 or 5 feet tall could house 400 to 500 of them.

“They really pack in tight to conserve heat,” Curtis explained.

The boxes can be even smaller. Penn State Extension’s “A Homeowner’s Guide to Northeastern Bats and Bat Problems” recommends boxes be at least 7 inches deep, 24 inches wide, and either 12 or 24 inches tall. According to the publication, boxes 12 inches in height will house up to 100 bats, and boxes 24 inches in height will house as many as 200 bats.

Curtis recommended installing the box built according to Penn State Extension’s instructions on a pole or a sturdy dead tree with few limbs, with full southern exposure. It could also be placed on the south-facing side of a barn.

Penn State Extension’s guide, which includes instructions on how to build a bat box, can be found online at:

Trees and shrubs and a water source could make a yard more bat-friendly, said Lori Severino, spokeswoman for the state Department of Environmental Conservation. n

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