White-nose syndrome, caused by the fungus Geomyces destructans, has decimated bat populations throughout eastern North America. Recent estimates show that 6 to7 million bats have succumbed to white-nose syndrome.
This fungus thrives in the cool, moist conditions found in many caves and mines where bats may also hibernate. Roger W. Perry, a research wildlife biologist with U.S. Forest Service Southern Pine Ecology unit recently published an updated review of bat hibernation and cave climates in the journal Environmental Reviews to aid managers and researchers working to address this disease.
“The emergence of white-nose syndrome refocused interest on the physical factors that influence cave climates and how cave climates could potentially interact with growth of the fungus and affect bat survival,” explains Perry. “I wanted to understand why caves just a short distance apart may potentially differ in white-nose syndrome infection and mortality and how the climate in a cave could influence fungal growth.”
Several different species of bats spend the winter in underground shelters. To survive on their limited fat reserves during winter, bats generally hibernate in structures that provide temperatures between 4 and 10oC (39-50oF). Caves and mines often provide these cool but above-freezing air temperatures. The high humidity in these underground shelters also helps reduce water loss in bats during hibernation.
Various factors can reduce or increase cave temperatures and result in favorable choices for hibernation. These factors include a caves size, depth, and topographic setting as well as the number of openings, elevation, airflow patterns, physical configuration, and water infiltration. Humidity in caves during winter depends on outside air temperature, airflow, evaporation rates, and condensation rates. “Unfortunately, these high humidity and low temperature conditions are perfect for growing Geomyces destructans, which grows best in cold, but above-freezing temperatures,” says Perry.
In regions where mean annual temperatures are not within the range of optimal growth for Geomyces destructans, many caves used by bats during winter may still harbor this lethal pathogen. “The climate within individual caves may make some more conducive than others for growth of this fungus, but right now we still dont know enough about this interaction to say for sure,” says Perry. “With the rapid spread of white-nose syndrome across the United States and the 90 to100 percent mortality in caves that have been infected with it, managers and researchers are in a race to find answers to slow or stop the spread.”
For more information, email Roger W. Perry at email@example.com