With a plague sweeping through North America’s bats, biologists at more than 40 national wildlife refuges in the Southeast have been cruising back roads and forest trails to map bat populations and assess the malady’s impact.

Bats aren’t easy to study. They emerge at night. Even if you are lucky enough to glimpse them silhouetted against the night sky, they’re tough to identify. And their chitter–chatter is too high for the human ear to hear.

How can you count animals you can’t hear and can barely see? David Richardson says the key is a bat detector — called an Anabat SD2 — that records the ultra–high frequency clicks and squeaks that bats use to navigate.

Richardson is a U.S. Fish and Wildlife Service terrestrial ecologist in Grenada, MS. He is the field coordinator for the mobile acoustical bat monitoring project, which is being managed by the National Wildlife Refuge System’s Southeast Region Inventory and Monitoring (I&M) Network.

The project involves biologists mounting an Anabat, a box not much bigger than a paperback, on a vehicle roof before starting a 10– to 30–mile census run. As the Anabat records, a synchronized global positioning system (GPS) plots the location of every call. After downloading the digital recordings into a computer, special software programs make it possible to count and, in most cases, identify the bat species.

Janet Ertel, deputy chief of the Southeast Region I&M Network, says this long–term monitoring effort has two goals. One is to discover what bats are out there using refuge habitat.

The second is to track the impact of deadly white–nose syndrome as it moves into the Southeast. The fungal infection, which typically appears as white fuzz on the face and wings of bats, spread to the United States from Europe. It was found first in New York in 2006, but it has proliferated rapidly since, killing more than 5.7 million North American bats. Experts consider it one of the most devastating threats to wildlife in eastern North America. In the Southeast, biologists are especially concerned about the gray, Indiana, small–footed, little brown, Northern long–eared, hoary, silver–haired and Eastern red bats as well as the Eastern pipistrelle.

The disease has crept as far south as Fern Cave National Wildlife Refuge, in northern Alabama, and as far west as northwest Arkansas. The fungus weakens bats and travels quickly through communal winter roosts. Some species, Richardson says, are in danger of becoming regionally extinct. So far, there’s no cure.

The picture is just coming into focus, according to Richardson and Nick Wirwa, a wildlife biologist who surveys bats at St. Catherine Creek, Cat Island and Bayou Cocodrie Refuges in Mississippi and Louisiana. Preliminary data show that some forests have a lot more bats than others.

For example, surveys near Fern Cave Refuge detected a dozen bats per mile, while those at other refuges found only two or three per mile. And bats appear to prefer forest edges and openings. The surveys — done in the first half of summer — also detected more bats in July than in June, probably because young of the year are on the wing.

Mobile acoustical bat monitoring project researchers hope they’ll end up with a clearer picture of how landscape–level factors such as habitat change, forest condition, climate change, wind farms and agriculture affect bats. They are also gaining a better understanding of bats on each refuge.

Ertel, who spent years studying bears, notes that bats are important predators, too. They may be small, she says, but they’re “a critical piece of our web of life.”

John Pancake is a freelance writer who lives in Goshen Pass, VA.