There are 12 species of bats that occur in Illinois; 5 of these species can be found hibernating in abandoned mines and caves in southern Illinois. Due to the destruction of their natural hibernacula, caves, many species of bats have found abandoned mines to be suitable replacement habitat. A complex of abandoned underground microcrystalline silica mines in southern Illinois owned by Unimin Specialty Minerals Corporation now provides hibernacula for 5 species of cavernicolous bats: the federally endangered Indiana bat (Myotis sodalis), little brown bat (M. lucifugus), eastern pipistrelle (Perimyotis subflavus), big brown bat (Eptesicus fuscus), and the northern long-eared bat (M. septentrionalis). Within the last 10 years the number of bats using these mines has increased dramatically, especially the Indiana bat which has increased from just over 9,000 to 43,000 hibernating in Magazine Mine. One concern of having so many endangered bats hibernating in one mine is stability. Mines were created relatively recently and are still in the process of settling. Thus, these mines might act as a potential sink, drawing in hibernating bats but potentially collapsing and killing them. Thirteen mines were surveyed for bats and for the amount of spalling that occurred over the 16-month study period from September 2006 to December 2007. Factors that could increase the amount of spalling were quantified, including temperature, moisture, and moisture variability in the material of the walls in the mines, and temperature variability. Number of hibernating bats in the mines was also documented. Data were analyzed with logistic regression. Temperature was a significant predictor of spalling (W2 = 12.76, p = 0.0004) when considered as a univariate variable, as was temperature variation (W2 = 21.89, p = <0.0001). Considering multiple logistic regression analyses, moisture was the best predictor. For the 13 mines surveyed, number of hibernating bats ranged from 0 to 3,755. Whereas all three variables were important at predicting the presence of bats, temperature variation (W2 = 35.98, p =<0.0001) was a better predictor than temperature or moisture. In a multiple logistic regression, temperature (W2 = 46.75, p = < 0.0001) and temperature variation (W2 = 20.56, p = < 0.0001) were better at predicting presence of bats then was moisture. The less variation in temperature the more likely that bats will be present. Because bats prefer stable temperatures and spalling occurs more often at high variability of temperatures and very low temperatures, bats were usually in areas that exhibited little or no spalling.

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