Preference for hibernacula microclimates varies among 3 bat species susceptible to white-nose syndrome

Abstract

Abstract North American bat populations have experienced precipitous declines since the introduction of white-nose syndrome (WNS). Evidence that bats have responded to WNS by altering their winter habitat selection has been used to manipulate underground environments and improve winter survival. However, such management practices must be based on local data, which do not exist for all regions. Our goal was to identify determinants of winter habitat use for 3 bat species with varying susceptibility to WNS. To do so, we conducted 188 surveys of 129 potential hibernacula over 3 winters. We found that the range of winter temperatures and presence of water were important for the Little Brown Myotis (Myotis lucifugus) and Tricolored Bat (Perimyotis subflavus), species that are highly susceptible to WNS. Counts of both species were greater in sites with a narrow (<5 °C) temperature range and where streams or water bodies >25 m2 were present. In addition, we found larger groups of Little Brown Myotis in abandoned railroad tunnels than in caves. Winter counts of these species increased over time at 3 railroad tunnels that were surveyed for 3 consecutive winters, whereas populations were extirpated from historically important caves and mines. Counts of Big Brown Bats (Eptesicus fuscus), which are less susceptible to WNS, were also greater in hibernacula with water bodies. However, average winter temperature also helped predict counts of Big Brown Bats. This species had a curvilinear response to temperature, with most bats found at hibernacula with average winter temperatures of 4 to 6 °C, and fewer bats observed at warmer and colder conditions. These data show that focusing solely on historically important hibernacula may fail to achieve conservation goals for the Little Brown Myotis and Tricolored Bat in our region, and suggest that anthropogenic structures can provide habitat for remnant populations of imperiled bat species.