Cave bats in crisis

Mammals > Cave bats in crisis: White-Nose Syndrome

A Little Brown Bat with White-Nose Syndrome.
This Little Brown Bat from Pennsylvania shows the classic sign of White-Nose Syndrome with a coating of white fungus on its nose. Cave bats in the Smokies are also infected.

USFWS photo courtesy of Ryan von Linden, NY Dept of Environmental Conservation.

Think extinction’s just for dinosaurs, dodos, and passenger pigeons? Think again. It’s happening now, all around us, as the deadly White-Nose Syndrome (linked to the fungus Pseudogymnoascus destructans) devastates populations of native bats.

A bat with White-Nose Syndrome has white fungus growing on its nose, toes, and wing webbing. One of the most at-risk bat species is the Little Brown Bat, because it hibernates in caves where the fungus grows. A social bat that’s common on the East Coast, the Little Brown is one of the bats you’re likely to see swooping across the sky at dusk. In the early 2000s, it numbered over 6.5 million, but scientists think that this entire species could be extinct in 20 or fewer years as White-Nose Syndrome spreads through U.S. caves.

How can scientists know when this bat might go extinct? Bat researchers from Boston University, the University of Santa Cruz, the New York State Department of Environmental Conservation, and the Pennsylvania Game Commission used a computer program that models cave-dwelling bat birth and death into the future. They first tested the model to see if it accurately predicted current bat populations by entering bat data from the past. It proved to be accurate in detailing bat births, survival rates, and deaths each year.

Pests such as biting mosquitoes may become more common as bat populations decline.
Pests such as this biting mosquito may become much more common in the next decades as bat populations plummet.

Open use photo courtesy of Alvesgaspar.

Enter the devastating White-Nose Syndrome. The scientists then used the computer model to figure out if Little Brown Bats would go extinct, or nearly so, in our lifetimes. The scientists ran the computer program to simulate bat births, infection with White-Nose Syndrome, and death over the next 100 years. To get rid of errors, they ran the same model 1000 times and analyzed the results with statistical tools.

What they found was grim. Researchers ran the models in two ways: the first assumed 45 percent mortality each year. That’s the constant rate of death from White-Nose Syndrome that we’ve seen in caves so far. According to this model, there is a 99 percent chance that the Little Brown Bat will be extinct in just 16 years. That is, by 2026, less than 0.01 percent of the population will be alive.

The second version of the model assumed that the disease might get less severe over time, or that some bats might build up resistance, so only 10 percent of the bats would die each year after the first few seasons of the disease. Yet even with this more conservative model there is a 90 percent chance that Little Brown Bats will be extinct within 65 years, by 2075.

What do these numbers mean? This is devastating news if you’re a Little Brown or other cave-roosting bat, because you’re very likely to get White-Nose Syndrome and very unlikely to survive it. But even if you’re not a bat, these numbers should be shocking. Bats are essential, if sometimes overlooked, parts of our ecosystem. Bats

  • typically eat up to 50 percent of their body weight in insects each night, reducing disease-carrying mosquito populations and swarms of crop pests
  • are pollinators of flowers and food, particularly of night-blooming plants that have no other way to reproduce
  • nourish the caves in which they live: just as we apply manure to our farm fields, bats fertilize otherwise barren cave floors with guano (bat poop), allowing microorganisms and cave life to thrive.

If we lose bats, we’re losing more than a single species: we also lose a key link in our ecosystem that can’t be replaced.

Research to understand White-Nose Syndrome is ongoing.
Many scientists are trying to understand White-Nose Syndrome and find a way to stop its fatal spread.

USFWS photo courtesy of Greg Thompson.

What to do? Based on their models, scientists estimate that for the Little Brown Bat to survive this century, we would need to see less than 5 percent of the population dying from White-Nose Syndrome each year. But because of the rapid spread of White-Nose Syndrome, and because we don’t know how we can help infected bats survive on a large scale, the future of cave-roosting bats is very uncertain.

What we do know is that we need more funding, time, and research to study White-Nose Syndrome. Only through massive efforts and intensive study can there be a hopeful future for cave-roosting bats in the eastern United States.

Find more information including videos, maps, and reports at the White Nose Syndrome Coordinated Response website.

Article referenced: Frick, W.F., Pollock, J. F. , Hicks, A.C., Langwig, K.E., Reynolds, D.S., Turner, G.G., Butchkiski, C.M., and Kunz, T.H. 2010. An emerging disease causes regional population collapse of a common North American bat species. Science 329. Accessed online at 6 August 2010.

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Last updated: July 13, 2015

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