USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

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Albany, CA 94710-0011
(510) 883-8830
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News Releases 2018

Researchers piece together disparate records as disease closes in on western bats

For Immediate Release: November 1, 2018

Contact: PSW Research Station Public Affairs,

A group of Townsend's big-eared bats roost together in a cave.
The majority of bats found hibernating in the western United States typically congregate in groups of 10 or fewer, like these Townsend’s big-eared bats in northern California. (U.S. Forest Service/Ted Weller)

ARCATA, Calif. — Conservation of bats has long been hindered by a lack of knowing their winter whereabouts, particularly in the western United States. With the confirmed case of white-nose syndrome in western Washington in 2016, a new impetus has been placed on finding these secluded roosts scattered across millions of acres to more closely track the disease and its effects.

National wildlife databases contained sparse and sporadic data on winter roosts of western bats. However, a concerted effort by the scientific community has produced one of the largest, most complete dataset of recorded hibernacula in the western United States.

"We knew from the research of others that the data had to exist," said Ted Weller, a wildlife biologist and bat specialist with the U.S. Forest Service’s Pacific Southwest Research Station, who was one of the leaders on the project. "We just needed to get it all in the same place."

Weller and his colleagues canvassed federal and state agencies, as well as the academic community, across 11 western states to amass 4,549 winter bat survey records. Their findings, detailed in "A Review of Bat Hibernacula Across the Western United States: Implications for White-Nose Syndrome Surveillance and Management," were released today online in PLoS One.

White-nose syndrome is a highly lethal fungus presumed to be spread among bats during their winter hibernations, where their wet, cool hibernacula are conducive to the syndrome’s pathology. Originally detected on the East Coast in 2006, the occurrence of white-nose syndrome in Washington state leap-frogged the disease’s western-most exposure by more than 800 miles, wildly outpacing its predicted rate of spread. And in the process, encapsulating the western bat population from both its eastern and western fronts.

The two most prevalent types of bats recorded in the surveys were bats within the genus Myotis and the Townsend’s big-eared bat (Corynorhinus townsendii).

In the 82 structures that were surveyed five or more times since 1990, researchers reported that bat populations were found to be stable. One somewhat encouraging finding was the relative seclusion in which bats roosted in the West. About 95 percent of Myotis encounters were of individuals or groups of 10 or fewer bats; 72 percent of Townsend’s big-eared bat encounters were similarly small.

"While such small roosting aggregations lead us to believe that there are a lot more hibernacula out there," Weller said, "the relative isolation of these species' roosting behavior could help mitigate the exposure or spread of white-nose syndrome."

Of the survey records, only four documented Myotis aggregations of 500 or more bats, each located in a separate state (Arizona, Idaho, Montana and New Mexico). Only six records documented Townsend’s big-eared bat aggregations in excess of 100 bats, five of those records occurring in Nevada mines.

Weller said he and his colleagues hope others will be able to build upon their work of pooling the surveys of others to produce a collective monitoring database. Toward that end, the researchers have made their research available as a public dataset. The dataset removes structure names and only provides a general location description to prevent disclosure of exact hibernacula locations.

"We acknowledge the legal and proprietary concerns surrounding data sharing," Weller said. "But the conservation community can no longer afford to lose occurrence records, especially when a unified effort could go a long way in monitoring hibernating bats in the face of disease or other emerging threats."

Headquartered in Albany, California, the Pacific Southwest Research Station is part of the U.S. Forest Service’s Research and Development branch developing and communicating science needed to sustain forest ecosystems and other benefits to nature and society. Pacific Southwest Research Station scientists are engaged in research across a network of 14 experimental watersheds, ranges and forests and eight research facilities in California, Hawaii and the U.S.–affiliated Pacific Islands. Research is organized into five research units: conservation of biodiversity, ecosystem function and health, fire and fuels, urban ecosystems and social dynamics, as well as Pacific Islands forestry. For more information, visit


Pacific Southwest Research Station/USDA Forest Service
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