Big Oaks Bat Surveys

We recently had a team from the Indiana Ecological Services Field Office come to the Refuge, despite the many challenges of weather and the situation in the federal government. The goal of the visit was to spend a day searching for tricolored bats (Perimyotis subflavus), previously known as the eastern pipistrelle hibernating in caves on the Refuge. Previous surveys to map caves on the Refuge in the 1990s, as well as cave biological inventories in the 2000s, established the presence of small numbers of tricolored bats using our caves, as well as a handful of northern long-eared bats and big brown bats. However, in the 2010s a devastating fungal pathogen spread through Indiana caves and across much of the country, causing white-nose syndrome (WNS) and killing countless bats. Tricolored bats have been badly hit, with a 91% decline seen in Indiana. Since then, no significant work has been done in the caves on the Refuge.

We all met at the office and agreed on routes to visit the caves where bats had previously been found. We split into different groups to tackle as many caves as possible. Some required long hikes into closed areas, where we encountered many artillery shells on our trip. Some of the caves were extremely tight and cramped. Others had some standing room inside, though not for the whole length. Almost all have a stream running inside, usually just a few inches deep, though in some cases over a foot. These areas provide habitat for cave crayfish and for tiny cave isopods, amphipods, and ostracods.

Cave salamanders were another common sight, and we even found a tiny salamander larva, likely of this species, swimming around in a stream. Several pickerel frogs were also hibernating in the cave, as well as herald moths and flies.

We were not disappointed and did find several tricolored bats: two caves had one each, and the largest on the Refuge, Bernice Chandler Cave, had 9 tricolored bats hibernating inside. This was impressive information, and these numbers were roughly equal with what was seen 20+ years ago. Though the numbers are small overall, it does show that Big Oaks continues to provide good hibernacula for overwintering tricolored bats, a species which has been proposed for listing as endangered.