Effects of mine characteristics on hibernacula selection by bats in southern Illinois

About 12 species of bats occur in Illinois, most of which hibernate during the winter. Because of destruction of natural habitats, many cavernicolous bat species rely on abandoned mines for hibernacula. In Alexander County in southern Illinois, abandoned underground microcrystalline silica mines, owned by Unimin Specialty Minerals Corporation, provide winter hibernacula for five species of bats: the federally endangered Indiana bat (Myotis sodalis), big brown bat (Eptesicus fuscus), little brown bat (M. lucifugus), northern long-eared bat ( M. septentrionalis), and eastern pipistrelle (Perimyotis subflavus). Within the last decade, the number of Indiana bats using these mines as hibernacula has risen dramatically. For example, Magazine mine now houses >30,000 hibernating Indiana bats. A total of 110 surveys of 45 abandoned mines was conducted between 2003 and 2007 in southern Illinois to determine predictive factors for the total number of bats as well as the number of each species using a mine. Factors measured included: size of the opening, number of openings, mean temperature during hibernation (November through March), temperature variability, distance to water, distance to nearest road, and evidence of disturbance. A total of 75,067 bats was observed hibernating in 43 mines. Three sets of data were analyzed were conducted. The first included data from all of the mines (N=45). The second set of analyses was limited to the 16 mines that contained temperature loggers. For this analysis, only loggers that were place near hibernating bats were used. The third set of analyses used the 16 mines with dataloggers, using both loggers that were placed near hibernating bats, as well as those loggers place where there were no bats hibernating. Univariate and multivariate regression analyses were run using these datasets. These mines are a very important resource for bats, and specifically Indiana bats. Ongoing efforts are being made to protect these mines and determine their long-term stability as bat hibernacula.