Tricolored bat with visible symptoms of WNS from Chickamauga and Chattanooga National Military Park, Georgia. Photo credit: National Park Service
This winter two scientists will set out to learn whether tricolored bats that use winter roosts other than caves and mines are susceptible to a deadly bat disease in the coastal plains and forests of North and South Carolina — two of 38 states in the bats’ range.
In the winter of 2016, Dr. Susan Loeb of the U.S. Forest Service and Clemson University and Assistant Professor David Jachowski of Clemson did a pilot study of tricolored bats roosting under two bridges in the upper coastal plain of South Carolina. They found that some bats left the bridge for several days and returned, suggesting that they were using alternate roosts. However, because the researchers did not track bats to these roosts, where the bats were going was unknown.
Now the researchers are expanding their study to find out what alternative roosting sites tricolored bats use and if the behavior of bats and environmental conditions there can protect them from the disease white-nose syndrome (WNS).
WNS, caused by the fungus, Pseudogymnoascus destructans, or Pd, was discovered in New York State in 2007. Now confirmed in 31 states and 5 Canadian provinces, the disease has wiped out some populations of several hibernating bat species, including tricolored bats. At hibernation sites where white-nose syndrome has affected tricolored bats, average overall declines of these bats have been more than 75 percent. As observed by Loeb, these declines have been even higher at some sites in the south.
In their pilot study, Loeb and Jachowski discovered that what sets coastal plain habitats apart is a striking potential difference in temperature tricolored bats encounter at more exposed and warmer sites than at mine and cave habitats.
Temperature is critical to the spread of the WNS fungus because any body temperatures above 64 degrees Fahrenheit might mean a greater chance for the bat’s immune system to fight the fungus over the winter, Loeb said.
She said, however, that such sites might be a double-edged sword. If body temperature remains high, a bat will be less able to enter an extended state of torpor, a short form of hibernation that can last only for a few days. Possibly because of the warmer climate, the coastal plains populations of tricolored bats might only hibernate on a daily basis to conserve energy.
If bats are able to escape WNS in these alternative habitats but remain more active due to higher outside temperatures, they must forage to survive. Finding available insects in the winter, even in the Carolinas’ warmer coastal plains, might be challenging for the beleaguered bats.
Now, with $125,925 funding from an FWS research grant, Loeb and Jachowski plan to expand their search for the bat’s winter habitat under bridges and in trees across the coastal plains of the Carolinas. They will be joining the ranks of other FWS-funded researchers such as Dr. Jeremy White in Nebraska and State Biologist Cory Mosby in Maine who have turned their attention to small bat hibernation habitats other than caves and mines.
“The decline of tricolored bats in the southeast is concerning. When the disease first arrived in the region, researchers expected it to not be as bad because the bats could forage. In some populations, we are seeing 90% declines.” – Susan Loeb
To measure body temperature and foraging, Loeb and Jachowski’s team will outfit temperature-sensitive radio transmitters on the bats at their winter roosts to document body temperatures and activity levels. They will use the transmitters to track bats to what might be an array of winter roosting types in this area free of caves and mines.
When the researchers capture the bats, they will swab and inspect them for the fungus and record data about the roost, such as tree height and cavity depth that might affect temperature. They will also collect fecal samples at the roost site and from the bats to determine whether the bats forage in winter.
Loeb said the study will contribute to a better understanding of bats’ susceptibility to WNS in the southeastern U.S. When the disease was first documented, researchers had hoped the region would host roosts that would be warmer than the northeastern caves and mines where the disease was first found, suggesting that the fungus would not spread to areas where wintering bats’ body temperatures would be higher than the critical 64-degree Fahrenheit threshold. In years since, however, researchers have found that even caves and mines in the southeast are cold enough to allow Pd to thrive.
“The decline of tricolored bats in the southeast is concerning,” Loeb added. “When the disease first arrived in the region, researchers expected it to not be as bad because the bats could forage. In some populations, we are seeing 90% declines.”
Now with exploration of alternative roosts in the southeast, scientists hope some tricolored bat populations might survive if they can find warm roosts and insects to eat during lean winter months. And in the race to help bats survive WNS, hope is a good place to start.