White-nose syndrome to blame for plummeting bat population

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After surpassing 300 as recently as 2016, the bat population at Spook Cave plummeted in the last two years, to just four bats in 2018. The culprit is a highly-contagious fungus called white-nose syndrome. Bat count volunteer Gary Siegwarth snapped this photo of local bats several years ago.

By Audrey Posten, North Iowa Times

For roughly 10 years, a group of local caving enthusiasts has made an annual late-February sojourn into Spook Cave, surveying and counting the bat population that’s taken up winter residence in the McGregor-area tourist attraction.

In the early years, around 100 bats could be seen, said volunteer Gary Siegwarth. That number grew over time, surpassing 300 as recently as 2016. Last year, however, the population plummeted, with only eight bats located. This year, the number shrunk again, as just four bats were observed.

The culprit, Siegwarth said, is white-nose syndrome, a contagious fungus that infects the skin of the muzzle, ears and wings of hibernating bats. Other populations in northeast Iowa and southwest Wisconsin have been similarly hit. According to the U.S. Geological Survey, the fast-spreading white-nose syndrome has killed millions of insect-eating bats in 31 states and five Canadian provinces since the winter of 2007-2008.

Signs of white-nose include excessive or unexplained mortality near the bats’ hibernation site, visible white fungal growth on the muzzle or wings of live or freshly dead bats, abnormal daytime activity or movement and severe wing damage in bats recently emerged from hibernation.

“We knew [the population] crashed last year,” Siegwarth said. “Before then, I’d noticed a lot of dead bats in January. It seemed really weird.”

Siegwarth said bats venture into caves each fall when their insect food supply disappears. Their small fat reserves help them survive the winter until insects are again available in the spring. But the fungus, he noted, increases the bats’ metabolisms, burning those precious fat stores.

“What happens is they’re starving; they only have so much fat reserves,” he explained. “So they go flying out of the cave in January. Unfortunately, there’s nothing out there for them, so they’re flying out of the cave and dying.”

Unfortunately, there are limited options available to stop the spread of white-nose. The fungus is easily transmitted, so Siegwarth advised against traveling from one cave to another, as well as staying out of hibernation sites when bats are in residence.

“When you go in Spook Cave in the summer, the bats aren’t there,” he said.

People can also put up bat houses. It may take some time, but Siegwarth said bats will eventually start to move in.

“For those that do survive, they might be more resistant,” he hedged. “You can help rebuild a more resilient population.”

Also sobering, said Siegwarth, is that the consequences of losing these bat populations is unknown. The major loss of an insect predator could impact both humans and crops.

“We had our chance. We have the Atlantic and Pacific Oceans,” he said. “Once it bridges that barrier, it’s hard to stop.”

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