Mystery Bat Die-Off
From white nose syndrome?
Thousands of hibernating bats are dying in caves in New York and Vermont from unknown causes, prompting an investigation by the New York State Department of Environmental Conservation (DEC), as well as wildlife agencies and researchers around the nation.
The most obvious symptom involved in the die-off is a white fungus encircling the noses of some, but not all, of the bats. Called “white nose syndrome,” the fungus is believed to be associated with the problem, but it may not necessarily contribute to the actual cause of death. It appears that the impacted bats deplete their fat reserves months before they would normally emerge from hibernation, and die as a result.
Until researchers understand the cause and how it is spread, state environmental officials and caving organizations are asking people not to enter caves or mines with bats until further notice to avoid the possible transfer of the disease from cave to cave. Vermont officials are making a similar request.
“What we’ve seen so far is unprecedented,’’ said Alan Hicks, DEC’s bat specialist. “Most bat researchers would agree that this is the gravest threat to bats they have ever seen. We have bat researchers, laboratories and caving groups across the country working to understand the cause of the problem and ways to contain it. Until we know more, we are asking people to stay away from known bat caves.”
Bat biologists across the country are evaluating strategies to monitor the presence of the disease and collect specimens for laboratory analysis. Biologists are taking precautions – using sanitary clothing and respirators when entering caves — to avoid spreading the disease in the process.
Bat populations are particularly vulnerable during hibernation as they congregate in large numbers in caves – in clusters of 300 per square foot in some locations — making them susceptible to disturbance or disease. The vast majority of the hundreds of thousands of bats known to hibernate in New York do so in just five caves and mines. Because bats migrate as far as hundreds of miles to their summer range, impacts to hibernating bats can have significant implications for bats throughout the Northeast.
Indiana bats, a state and federally endangered species, are perhaps the most vulnerable. Half the estimated 52,000 Indiana bats that hibernate in New York are located in just one former mine – a mine that is now infected with white nose syndrome. Eastern pipistrelle, northern long-eared and little brown bats are also dying. Little brown bats, the most common hibernating species in the state, have sustained the largest number of deaths.
“impacted bats deplete their fat reserves months before they would normally emerge from hibernation..”" sounds very odd, especially as the classic model of hibernation, where an animal sleeps away the entire winter, is not true for Indiana bats.
Bats arouse (awaken) from hibernation periodically and pontaneously during the season of hibernation. The mean length of the period of hibernation between arousals for the Indiana bat under natural conditions is 13.1 days. Arousal is energy expensive, equivalent to about 65 days of hibernation. There are also other physiological costs of metabolic depression. It is likely bats trade off the costs of
metabolic depression with costs of less efficient hibernation, using available energy to minimize the duration and depth of hibernation. During arousal, bats select where they will spend the next period of hibernation. It is probable they use behavior and social interaction to help them make this selection.
According to the above .pdf, it can also be too cold for hibernation of be successful.
However, there are physiological constraints on minimum body temperatures. If bats get too cold they must use energy to warm themselves or freeze. At 0.5°C, energy expenditure is four times that at 2°C.
So, are the temperatures colder than normal in New England this year? That appears to be the case, at least in some parts of the region.