A review of factors affecting cave climates for hibernating bats in temperate North America

The fungal pathogen Geomyces destructans, which causes white-nose syndrome in bats, thrives in the cold and moist conditions found in caves where bats hibernate. To aid managers and researchers address this disease, an updated and accessible review of cave hibernacula and cave microclimates is presented. To maximize energy savings and reduce evaporative water loss during winter, most temperate vespertilionid bats in North America select caves with temperatures between 2 and 10 degrees C, with 60%-100% relative humidity. Generally, the temperature in caves is similar to the mean annual surface temperature (MAST) of a region, which varies by latitude, altitude, and topography. However, MAST for most areas where caves are found in eastern North America is well above 10 degrees C. Thus, various factors cause cold-air infiltration that reduces temperatures of these caves during winter. These factors include depth of cave, topographic setting, airflow patterns, cave configuration, and water infiltration. Factors affecting humidity, condensation, and evaporation are also addressed. In areas where MAST is above or below the thermal requirements of Geomyces destructans, many caves used by bats as hibernacula may still provide favorable sites for optimal growth of this fungus.