Inside a Bat Hibernaculum
In the fall of 2018, employees of the Wyoming Game and Fish Department (WGFD), along with volunteers from the Hole-In-the-Wall Grotto and the Northern Rocky Mountain Grotto, entered a cave in the Bighorn Mountains to determine if it is a hibernaculum, or hibernation site, for bats.
The cave entrance is located on a high, windswept ridge where drifted snow piles up quickly, according to a press release. The team used ropes and vertical caving techniques to access the near-vertical opening. After rappelling into the cave one at a time, they used headlamps to search walls and crevices in the ceiling for bats as they walked and crawled through the 600 feet of horizontal passage in the cave.
The survey identified five mouse-eared bats (Myotis genus) and seven Townsend’s big-eared bats, which were already hibernating for the winter. The stable, cold, subterranean climate allows bats to lower their metabolism to conserve energy. They will only arouse infrequently throughout the winter to allow their bodies to clear metabolic waste.
This survey is a part of an ongoing effort to better understand the fungus that causes white-nose syndrome (WNS), which causes bats to use their stored fat more quickly, resulting in death from starvation or from exposure when they emerge into unforgiving winter conditions to search for food.
WNS was detected for the first time in Wyoming in May of 2018 at the Fort Laramie National Historic Site. Subsequently, the Wyoming Game and Fish Department was awarded $29,437 to broaden white-nose monitoring and tracking of the little brown myotis bat to evaluate how they use their surroundings in the winter. Although most of the bats caught during statewide bat surveys are from the Myotis genus, relatively few of these are found during winter cave surveys.
“We have only found seven little brown myotis hibernacula,” WGFD nongame bird and mammal supervisor Zack Walker said in a press release. “This suggests the majority of little brown myotis go undetected and are never swabbed with the standard winter survey method.”