Deadly Bat Fungus Detected in California

A deadly fungus that has devastated bat populations across North America has now been detected in multiple counties throughout California, raising alarms among wildlife officials and conservationists.
The fungus, which causes the disease known as white-nose syndrome, has been confirmed in bat roosts in Humboldt, Sutter, Placer, Amador, and Inyo counties, according to the California Department of Fish and Wildlife (CDFW).
Preliminary tests also suggest the fungus may be present in several other counties, though more analysis is still underway.
While the visible symptoms of white-nose syndrome have not yet been observed in any California bats, the presence of the fungus itself is a major cause for concern. The disease has decimated bat colonies in other parts of the country, with mortality rates often exceeding 70 percent.
“This is essentially a death sentence for bats. Many of the affected populations are completely wiped out,” Eyal Frank, an assistant professor at the Harris School of Public Policy, previously told Newsweek.
Bats play a vital role in ecosystems and agriculture. A single bat can consume thousands of insects per night, providing crucial natural pest control that benefits both natural landscapes and croplands.
However, when bat populations plummet, farmers often increase pesticide use to compensate—a change that has been linked to additional human health impacts.
“When insect-eating bat populations declined in the United States, farmers responded,” Frank said. “And they compensate with more insecticides to make up for the loss in biological pest control. However, that results in adverse health consequences because pesticides are toxic compounds by design.”
A study published by Frank earlier this year showed that this trickle-down effect may have led to over 1,000 additional infant mortalities in the U.S.
Since 2016, biologists with CDFW, the National Park Service and the U.S. Fish and Wildlife Service have been regularly sampling California’s bat populations to monitor the spread of the white-nose syndrome fungus.
When bats emerge from hibernation each spring, they are swabbed and tested for the presence of the fungus.
While no visible signs of the disease have been reported yet, the confirmed detection of the fungus suggests it could begin impacting California’s 25 bat species in the coming years, mirroring the devastating pattern seen across the rest of the country.
Continued surveillance and monitoring will be crucial to understanding the threat and informing potential management strategies.
In the meantime, CDFW urges the public to avoid handling any wildlife, especially bats that appear sick or dead. Sightings of unusual bat behavior, such as flying or roosting during the winter months, should be reported to help wildlife officials track the fungus spread.
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