KENNEWICK — The fungus that causes white nose syndrome appears to have killed more than 1,000 bats within the last year in the large colony that spends summers at the Hanford site in Eastern Washington.
It is one of two known “mass mortality” events caused by white nose syndrome in Washington state since the fungus was first found in the state in 2016, said Abby Tobin, bat species lead for Washington state Department of Fish and Wildlife. The other die off area was in King County.
Two large underground structures at Hanford were left intact as environmental cleanup was being done on obsolete structures along the Columbia River near the F and D Reactors, which were once used to produce plutonium for the Nation’s nuclear weapons program at the Hanford site.
In 2006, a colony of bats was found roosting in the F Reactor clearwell, an underground concrete structure once used to store purified Columbia River water for the reactor before it was decommissioned in 1965, prompting officials to save the structure as bat habitat.
A few years later bats also were found in buildings near D Reactor, and the clearwell there was left in place. A maternity colony of bats quickly took up residence.
As the fungus spread from the Seattle area east across Washington state, it was detected in one of the clearwells last year, making it the first detection in Benton County and the farthest east in the state.
But no sick bats were found until the late winter of 2024. Then Hanford workers began finding dead bats in buildings near the sealed-up D Reactor.
“It was not something we looked forward to seeing,” said Justin Wilde, a biologist for Hanford Mission Integration Solutions. “We knew it was probably going to get here. We had kept it away for a long time but it seemed somewhere along the line a few of the bats got into the fungus that turned into white nose syndrome.”
Half as many Hanford bats
The dead bats appeared to have starved and had wing damage, both indications of white nose syndrome. Testing by Department of Fish and Wildlife confirmed they had the disease.
In a summer 2023 survey of the clearwells, about 2,500 bats were found in the D Reactor clearwell and about 1,000 in the F Reactor site.
But this past summer only about half as many bats were found living in the clearwells.
“It’s a pretty devastating wildlife disease,” said Cole Lindsey, a biologist for Department of Energy contractor Hanford Mission Integration Solutions at Hanford.
Hanford biologists will continue long-term monitoring of the Hanford bat colony to see how the population fares. The disease has been documented to wipe out 90% of the population of some bat colonies.
The two Hanford clearwells are maternity roosts where females spend the spring and summer roosting while each raises a single pup.
It is a unique roosting site in an area where large colonies are pretty rare or unknown, Lindsey said.
When the weather gets too cool for bats to find the insects they need, the colony disperses.
Not much is known about where the colony goes to hibernate. Some do remain in the Hanford area just north of Richland, Wash., as shown by bat detectors that detect bat calls which are at too high frequency for the human ear.
But large numbers of bats have not been found on the Hanford site in the winter, and it is not documented where they go to hibernate, Wilde said.
Biologists suspect they migrate regionally, flying to a higher elevation with consistent cold temperatures through the winter, Lindsey said.
Infected bats may starve
Bats with white nose syndrome emerge early from hibernation and return to their summer roost, where they have found water and food in the past, Tobin said.
About 30 emaciated, dead bats were found this year in buildings near the former D Reactor, which was enough to declare a mass mortality event.
The fungus Pseudogymnoascus destructans, which causes white nose syndrome, attacks the skin of hibernating bats and damages their wings, making it difficult for them to fly. Infected bats often leave hibernation too early, which causes them to deplete their fat reserves and become dehydrated or starve to death, according to the Fish and Wildlife Department.
The bats that use the clearwells are Yuma myotis, one of four Washington state bat species with confirmed cases.
They have furry brown bodies and black wings and are smaller than the silver-hared bat that is more commonly seen roosting in attics in the Tri-Cities.
Each Yuma myotis weighs about 6 to 8 grams — less than two nickels — and has a body smaller than a mouse. But they look bigger in flight because of a wing span that stretches 6 to 8 inches.
In one night they might eat their weight in small insects such as the mosquitoes and midges that are plentiful along the nearby Columbia River.
When biologists do monitoring near the river mosquitoes start bothering them at sunset, but when bats emerge from the clearwells “all of a sudden the mosquitoes are not as pesky for you anymore,” Wilde said.
Value of bats
Bats are valuable members of the ecosystem, with a single colony of bats able to consume tons of insects, according to the Fish and Wildlife Department. It says bats save U.S. farmers more than $3 billion a year in pest control costs.
Benton County is one of nine counties in Washington with confirmed cases of white nose syndrome and the farthest east. The fungus that cause the disease has been found in 13 additional counties.
It is spread from bat to bat, or a bat may contaminate a roosting area to allow the fungus to spread to other bats. People also can carry the fungal spores on their clothing, shoes or recreational equipment.
The fungus that causes the bat disease does not affect people, livestock or other wildlife.
The Hanford colony of Yuma myotis is the only one known in Benton County, but the Department of Fish and Wildlife would like to hear from you if you know of any other colonies of the species in the county.
You can report bat colonies at wdfw.wa.gov/bats at the link under “How You can Help.”
