Populations of bats diminished by white-nose syndrome (WNS), a disease of hibernating bats, are unlikely to return to healthy levels in the near future, according to new U.S. Geological Survey research. 

USGS and U.S. Fish and Wildlife Service scientists recently evaluated the potential for populations of little brown bats in the eastern United States that survive WNS outbreaks to repopulate. The scientists estimated that between 2016 and 2018, little brown bat populations that once contained millions of bats could decrease to lower than 100,000 animals. Also, some populations may not begin to increase again until around 2023. Populations east of the 100^th meridian, the designation between the drier western and wetter eastern states, would likely consist of sparse remnant communities, some of which may be less than 1.5 percent of their original sizes. 

This scarcity of surviving bats can negatively affect reproduction rates and make survivors more vulnerable to threats.

“With so few surviving animals, little brown bats could cease to be a dominant bat species in the eastern United States,” said USGS scientist Robin Russell, the lead author of the report. “These small bat population sizes are problematic because they are more likely to be wiped out by events such as poor weather conditions and landscape development.” 

Animals in small communities could also have trouble finding mates. Female bats gathering in maternity roosts during the summer can include several hundred bats, and the inability to form these colonies due to reduced populations may negatively impact overall reproduction rates. 

Bats pollinate plants, spread seeds and save us billions of dollars in pest control each year by eating harmful insects. WNS, caused by the Pseudogymnoascus destructans fungus, can cause up to 100 percent mortality in some little brown bat populations. It has already killed millions of hibernating bats in North America and continues to spread.

As part of a coordinated response to WNS, scientists from around the world are working to further understand the disease and conserve bat species affected by it. The USGS and USFWS are among numerous state, federal, tribal, private and university partners engaged in WNS research and response. Members of this community are pursuing multiple approaches to manage the disease, with treatment strategies to both reduce impacts of the disease and to improve the potential for bat populations to survive and eventually recover. This new study emphasizes the importance of continuing research on bat species affected by WNS to finding a solution for managing the disease. 

For more information about USGS WNS research, please visit the USGS National Wildlife Health Center website.