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Warm Wishes for Ailing Bats

Researchers suggest using space heaters to warms bats' chilly roosting caves, perhaps stalling the die-off associated with white-nose syndrome.

Though scientists are still perplexed about the origin of white-nose syndrome, and why it is such an efficient killer of bats, a team of researchers announced last week in Frontiers in Ecology and Environment that they may have discovered a means to lower the death rate in affected caves. Rather than focusing on fighting the fungus that causes the disease, they plan to target the animal's behavior and environment.

Justin Boyles, a graduate student in biology at Indiana State University and Craig Willis, a bat researcher at the University of Winnipeg, propose installing space heaters in bat caves during the winter. And experts familiar with WNS say their concept may hold considerable merit.

Boyles says hibernating mammals do not merely sleep during the winter, but they also lower their body temperature and metabolic functions to conserve energy, surviving off their fat reserves until spring when the temperature warms and food sources return.

But hibernation is not a static state.

Virgil Brack, chief scientist with Environmental Consulting and Innovations in Cincinnati and assistant director of the Indiana State University Bat Center, said that when mammals hibernate they fluctuate between two different states: long sleep phases interrupted by brief periodic waking phases throughout the winter.

In cave bats, Brack — who has been studying bat hibernation patterns for more than 30 years — said the periodic roused states typically occur every 10 to 14 days, and last just a few hours per episode. However he says, that's when they consume the most energy. For bats trying to keep warm in frigid caves, "It's a short but very energy-expensive time," he says. To help conserve while they're awake, Brack says bats normally fly to areas of the cave that are naturally a bit warmer than the chambers where they sleep.

Experts studying WNS have theorized that afflicted bats either rouse more frequently than normal, or stay awake for longer periods, when they do rouse. They expend their fat reserves too quickly, starving before spring arrives.

Boyles suggests that restlessness among bats suffering WNS might be predictable in an animal suffering a fungal infection. "There are a couple of possibilities. It's like athlete's foot: It could be itchy or it could be an immune response that that raises their temperature and causes them to wake up."

Working with Brack and other researchers, Boyles performed thermal imaging surveys of hibernacula and combined the results with bat population data collected over a number of years. He fed this data into an existing bat population and energy expenditure modeling exercise, then added data to represent the effects of WNS on energy consumption.

Boyles says the results correlated well with WNS mortality rates observed in the real-life caves. Furthermore, the simulation strengthened the conclusion that high mortality rates among bats with WNS might derive from the afflicted bats' abnormally high levels of wintertime activity.

Boyles ran a further simulation, factoring in the introduction of an artificial heating unit to his hypothetical cave. In Frontiers in Ecology, he reported the exercise mortality fell to 8 percent — a figure Boyles said would permit reasonable rate of survival.

"The question we want to answer first is whether the bats will find these artificial heat sources and whether they will use them," he said.

Nevertheless, Boyles told there is a chance that the heating could provide some additional benefit. The warmer temperatures might suppress the growth of the cold-loving fungus on the individuals that take advantage of the heat source. "We're heating it up pretty warm — around 70 to 80 degrees," well above the optimal temperature for the fungus, and that may help clear up the problem for some individual bats.

"But that's not the main point."

During the tryout phase of the solar-powered-heater prototype, the researchers intend to avoid caves already hit by white-nose. "We don't want to take the chance of increasing the survival rate of infected bats and give them the opportunity to spread the disease further," Boyles said.

They are in a hurry to see results, and Willis will be conducting the initial tests of the system this very winter in hibernacula in Manitoba where the disease has not yet been reported.

Boyles and Brack agree the heating idea is only a stopgap measure.

Sadly, even if the bats survive and thrive in the summer skies, the fungus will still be there in the cave environment waiting for them to return next winter.

"It probably won't hurt," Brack said, "if they got another two years. It gives us just that much more time to figure out a solution."

Brack adds that the WNS outbreak "has many of the characteristics of an exotic invasive. If it can be determined where it came from, we can see if there are some natural measures of control at work there that keep it from being so devastating."

Brack told that European researchers are doing what they can to help trace the source, but he says that there is an urgent need for dedicated funding to support this international cooperation.