Jan. 8 (UPI) -- Bats suffering from white-nose syndrome frequently make the unfortunate decision to spend the winter in warmer underground hideouts, places more likely to encourage fungal growth.
This disease-induced subterranean self-harm, described Friday in the journal Nature Communications, is a type of "ecological trap." By altering the infected animal's behavior, the disease gains the upper hand.
Researchers have been monitoring the wintering patterns of little brown bat, Myotis lucifugus, populations in Michigan and Wisconsin since 2012, before white nose syndrome first arrived in the two Midwest states.
Thanks to their detailed record keeping of environmental conditions inside hibernation sites, researchers were able to identify changes in the wintering preferences of little brown after white-nose syndrome began infecting local populations.
"We see that there is a shift across the regional bat population over time," lead study author Skylar Hopkins said in a press release.
"When we look at the population post-invasion, we see that more than 50 percent of the bats are still choosing to roost in warmer sites, even though colder sites are available. But on average, bat roosting temperatures have declined, because the colder-roosting bats have had higher survival rates," said Hopkins, who conducted the research while a postdoctoral scholar at Virginia Tech.
Scientists used what's called the mark-recapture technique to measure the effect of hibernation temperatures on survival rates. The method involves banding specimens and then trying to find them weeks or months later.
Researchers checked on their banded bats early during the hibernation period, before bats had settled in to their winter slumber, and then weeks later, before bats emerged from hibernation.
Scientists assumed that bats present during the first relocation attempt but missing during the second had abandoned their hibernation site and perished. Bats that ramp up their metabolism prior to spring are unlikely to survive the cold, insect-free Midwest winter.
Using swabs, researchers measured the fungal loads present on bats in different hibernation sites. The data showed the fungus responsible for white-nose syndrome is able to proliferate more rapidly in warmer wintering locations.
"Because we know that bats are doing better in the cold sites, the cold sites may be good ones for us to conserve," said Hopkins. "We can also think more about the warm sites that are acting as ecological traps and whether we should be trying to manage those sites in a different way.
"Maybe there are interventions that should be done at those sites to prevent most of the population from going there each year and having these big mortality events," said Hopkins.
While wildlife managers might be tempted to close-off dangerously warm wintering locations, researchers suggest the strategy could negatively affect other bat species.
Researchers in Michigan and Pennsylvania are using solar-powered air pumps to cool down wintering sites that are too warm, but it's not yet clear whether the strategy will improve the survival rates of bats infected with white-nose syndrome.
Scientists suspect humidity also plays a role in the spread of fungal disease. But measuring slight humidity differences in wintering locations, all of which are rather humid, is quite difficult.
"We've designed new humidity loggers to collect better humidity data than has been possible before," said Hopkins, now an assistant professor at North Carolina State University.
"These loggers are already deployed in caves and mines across the eastern United States, so we hope to soon understand how humidity has played a role in bat population declines, if at all," Hopkins said.