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America’s Most Common Bat Headed for Eastern Extinction

By the time today’s toddlers graduate from high school, the most common bat in North America may have vanished altogether from the eastern United States.

Researchers combined historical population trends with mortality counts in Myotis lucifugus colonies struck by White-Nose Syndrome, an extraordinarily virulent bat disease first identified in 2006. According to their models, M. lucifugus, better known as the little brown bat, has a 99 percent chance of vanishing from the east, soon.

“If mortality and spread continue the way it has in the past four years, that’s where we get the very distressing prediction of a high chance of regional extinction in 16 to 20 years,” said Winifred Frick, a Boston University bat researcher.

White-Nose Syndrome — shortened to WNS, and named after a fungus that grows on infected bats, which become weakened and die after waking too soon from hibernation — was first found in upstate New York. Since then it’s spread through caves as far south as Tennessee, and west as far as Oklahoma. In some caves, mortality is almost total. Caves where bats lived since the last Ice Age now stand silent.

Much remains to be learned about how WNS spreads, how it kills and where it came from, none of which is known for certain. Some researchers have proposed spraying caves with fungicides, but none have proved effective. Immunization is even more hypothetical. The disease is so new that scientists are only now agreeing that the fungus is likely a cause, rather than a symptom.

All that’s certain is bats are dying. More than a million have died so far, a die-off comparable to slaughters of passenger pigeons or Great Plains bison, only faster. Scientists have declared it “the most precipitous decline of North American wildlife in recorded history,” a diagnosis quantified by the new little brown bat predictions, published August 5 in Science.

“Yes, we had the empirical observations that cave floors were littered with dead bats. We knew this was a devastating problem. But nobody had quantified the impact to the populations,” said Frick. “We didn’t know what those die-offs meant to population viability as a species.”

The researchers combined long-term little brown bat population records gathered by wildlife officials in New York and Pennsylvania with their own long-term records of year-to-year variability in individual populations. This allowed them to model pre-WNS rates of breeding and natural population fluctuation.

Into this they plugged mortality rates from infected colonies. They ran the model thousands of times, the aggregated results producing probability curves of future survival. Almost invariably, the curve hits zero in a matter of decades. Even if WNS leaves survivors, the colonies will likely be so small that some inevitable coincidence — a tough winter, another disease, a run of bad luck — could wipe them out.

The researchers also modeled what will happen if WNS mortality declines. “You get a longer time frame to extinction, and that’s good. The crash isn’t so precipitous, so rapid,” said Frick. “But you still have to get the declines to less than five percent per year” before eastern little brown bats last beyond the century. As of now, five percent mortality looks like a pipe dream.

In a commentary accompanying the findings, former Consortium for Conservation Medicine director Peter Daszak, called the study “convincing evidence that this pathogen causes catastrophic population declines or has the potential to cause extinction. ”

The researchers don’t want their findings to be cause for defeatism, but to emphasize the urgency of stopping WNS.

Bats like M. lucifugus — and the eight other species in which WNS has now been found — are crucial to cave ecosystems, which rely on nutrients captured on the wing and delivered in bat droppings. Of more utilitarian importance to people, cave-dwelling eat vast amounts of crop-infesting insects.

In the last two years, White-Nose Syndrome was first detected in the agriculture-rich Midwest. If patterns from the east hold, mass die-offs will begin in two to three years.

“There are massive colonies in Tennessee, Kentucky, southern Illinois, parts of Oklahoma,” said study co-author Thomas Kunz, also a Boston University bat ecologist. “Those are are bats in agricultural parts of the world. We can expect economic and ecological consequences.”

In 2006, before the WNS outbreak, Kunz published a study estimating the economic value of insect-eating bats in an eight-county region of southwest Texas at about $1 million in pesticide costs alone.

That figure is rough but instructive. It also amounts to nearly half of what the U.S. government has allotted for White-Nose research.

Last year, Kunz was part of a delegation representing the U.S. bat research community who asked Congress for $50 million over the next five years. They were given $1.9 million, a pittance shared not only between them, but with researchers from the federal Fish and Wildlife Service. Without research funding raised by Bat Conservation International, the science would be at a crawl.

Presented with more proposals than they could fund, the researchers petitioned Congress for another $6 million this spring, said Kunz. They have yet to receive a response.

Images: 1) M. A. Tuttle, Bat Conservation International. 2) Graph of predicted little brown bat populations in the east under a range of WNS mortality rates. 3) Map of White Nose Syndrome spread. The palest shades of red signify sites of detection in 2006; the colors grow darker by year, with the darkest in 2010./Science.

See Also:

Citations: “An Emerging Disease Causes Regional Population Collapse of a Common North American Bat Species.” By Winifred F. Frick, Jacob F. Pollock, Alan C. Hicks, Kate E. Langwig, D. Scott Reynolds, Gregory G. Turner, Calvin M. Butchkoski, Thomas H. Kunz. Science, Vol 329, Issue 5992, August 6, 2010.

“Bats, in Black and White.” By Peter Daszak. Science, Vol 329, Issue 5992, August 6, 2010.
Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
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