Countdown to Extinction for Little Brown Bat

In the video above, CAS’s Thomas Kunz and Winifred Frick discuss white nose syndrome and its implications for the little brown bat, which Kunz says could become extinct in the Northeast within 20 years.

Little brown bats, those unwelcome summer intruders in barns and houses, but an ecologically essential eater of pestilent insects, may be extinct in the Northeast within 16 years, BU-led researchers predict.

The prediction comes in a paper in the current issue of the journal Science. The bats, found throughout North America, are dying from the mysterious white-nose syndrome (WNS). The disease has been annihilating bat populations in the northeastern United States since 2006, when it first appeared in New York state.

“Our analysis indicates that at least 73 percent of little brown bats in the Northeast have died in the last four years,” says Thomas Kunz, a College of Arts & Sciences professor of biology and director of BU’s Center for Ecology & Conservation Biology. Kunz assembled a team of researchers, including scientists from BU and the University of California, Santa Cruz, who used computer models to estimate the timeline to possible extinction.

It’s not clear how WNS, named for the bleached fungus found on victims’ noses and other body parts, kills. What is known is that afflicted bats rouse early from hibernation, become active, and lose body fat, starving to death. The fungus has been found as far away as Oklahoma, but has been devastating in the Northeast.

Even if the death rate decreases, the paper says, the little brown bat population will collapse in less than 20 years, from 6.5 million before the disease to 65,000, with a 90 percent chance of extinction within 65 years.

“Our results paint a grim picture of a once-healthy population of an abundant and widely distributed species now experiencing unprecedented losses,” the authors write.

Winifred Frick, the lead author and a postdoctoral fellow at BU and UC, says that “it was startling to realize just how severe the die-off is. It is very difficult to say how best to stave off extinction. We don’t have a silver bullet yet.”

“We should care about why the bats are dying,” Kunz says. They gorge on bugs that attack crops and trees and that carry disease, including mosquitoes bearing West Nile virus. WNS has killed one million Northeastern bats in the last four years, and “each year, those million bats would have eaten 694 tons of insects,” he says, and since “bats are natural pesticides,” human health would be affected by an increased need for chemical pesticides.

“The work Tom and his colleagues have done is really fundamental to a better understanding of these processes,” says John P. Hayes, a University of Florida professor and chairman of the school’s wildlife ecology and conservation department, who reviewed an earlier version of the paper before publication. “If you had asked me five years ago the probability that that species of bat would be functionally extinct from the Northeast in my lifetime, I would have said zero. My reading of the science is that the work that they did is solid.”

The first year the disease struck, only 5 to 10 percent of affected bats died, according to Kunz. The death rate then leapt exponentially, as the disease wiped out entire hibernating colonies in the following two years. “Bats can move the fungus around,” he says. “Once an animal is infected, they’re carrying the spores with them. Because bats are highly gregarious, disease transmission is certainly expected to be higher.” The fungus grows only at temperatures found during hibernation, so you won’t see the disease’s snow-nosed giveaway this time of year.

Hope may lie in a vaccine, which scientists are working on, Kunz says. Alternatively, evolution may save the bats, as disease-resistant individuals breed and pass on their hardiness, allowing the species to adapt its way out of the crisis. But don’t count on it, cautions Kunz: “Bats have very low reproductive rates. They typically produce one baby a year, sometimes two, in a single litter. I’ve worked with bats over 45 years. Never have I seen, or known about from the literature, of any mortality comparable to what we’re seeing.

“It’s very frustrating. In Vermont last year, I picked up 16 little bands that I’d put on bats over 20 years ago, all on dead bats.”

Rich Barlow can be reached at barlowr@bu.edu.