Tri-colored bats & white-nose syndrome

Some bats are responding by changing roosting behavior during hibernation

people in white lab suits stand in a tunnel
Susan Loeb and her colleagues survey bats in Stumphouse Tunnel, South Carolina. Photo by Ben Neece, USDA Forest Service volunteer.

The only mammal that truly flies, bats are celebrated for many reasons. Including their looks.

“Tri-colored bats are the cutest little things,” says Susan Loeb of the USDA Forest Service. “They’re tiny – they weigh less than a quarter of an ounce. And each one of their hairs has three colors on it: yellow, black, and reddish brown.”

Like almost all the 47 bat species in the U.S., tri-colored bats (Perimyotis subflavus) eat insects. And although they are tiny, tri-colored bats can eat up to half their body weight every night. It adds up. Bats eat so many bugs that they are a huge help to farmers and save the agricultural industry billions of dollars every year.

Tri-colored bats are among the species hit hard by white-nose syndrome, a fungal disease that has killed millions of bats since it was first detected in the U.S. in 2006.

In some places, the disease has killed more than 90 percent of tri-colored bats. Stumphouse Tunnel in South Carolina is one of these places. Loeb and her colleagues have monitored bats in the tunnel for years.

More than 300 tri-colored bats spent the winter of 2013-2014 hibernating in the tunnel. When Loeb and her colleagues counted bats in early 2014, they detected white-nose syndrome on half of the bats they sampled, although none were sick yet.

But by 2015, half the bats from the previous year were gone. “We can only assume they were all dead,” says Loeb. “It was really depressing. That was a tough day.” And in 2016, half the remaining bats were dead.

a bat roosts in a cave
Tri-colored bats are so tiny that they are called microbats. Photo by Ann Froschauer, U.S. Fish and Wildlife Service.

Today, Loeb is cautiously optimistic. Since 2019, the tri-colored bat population in this tunnel has stabilized and even slightly increased. Loeb’s recent study also shows that the bats have changed their behavior – a lot of them now roost in a colder part of the tunnel, which they didn’t do before white-nose syndrome hit. This suggests that habitat modifications could help save the species.

The U.S. Fish and Wildlife Service recently proposed listing tri-colored bats as endangered due to white-nose syndrome. Without monitoring efforts like the ones Loeb has contributed to, no one would know about the apocalyptic losses of this species. In fact, Loeb led the team that developed the North American Bat Monitoring Program, which has provided a lot of data on tri-colored bats and other species. Individuals, universities, national forests, state agencies, and many other groups help collect these data.

How else can people help bats? There are a few things individuals can do:

  • Help spread the word: Bats belong in our forests, fields, and grasslands. Tell your friends and family how interesting and helpful bats are.
  • Help keep the night sky dark by minimizing artificial light at night.
  • Choose plants that provide food and shelter to pollinators and reduce the use of pesticides.
  • When it’s safe to do so, leave standing dead trees for bats to roost in.
  • If you steward any forested land, consider managing for large oak trees and open forests. Bats don’t like a cluttered midstory.
  • Leave them alone! Don’t bother bats.

Read the full text of the study.

For more information, email Susan Loeb at

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