Vampire bat (Desmodus rotundus). Credit: Mileniusz Spanowicz/WCS.

By Sarah Olson
October 31, 2016

ats have long been associated with the dark and deadly, most infamously in the form of that monstrous prowler of the night, Dracula — in search of fresh blood to feed his thirst and claim new victims. On Halloweens of late, however, it is bats who have had a monster to fear — a real one — that is devastating populations of these flying mammals in eastern North America.

The villain is an introduced fungus that has compromised the bat’s ability to survive winters by matching its energy consumption to expected expenditure. Normally, healthy bats do this by eating insects and putting on the fat in the fall. The stored fat is used to survive until spring — sometimes for a period of more than six months.

In the winter, hibernating bats use the cellphone equivalent of sleep mode, greatly reducing their metabolic rates and body temperatures. In hibernation slumber, a bat’s pulse and breathing rate shrink to around once per minute. Their body temperature can drop below 50˚F. From this state, they regularly arouse and warm to 98˚F, but just like your cellphone, waking burns stored energy at a higher rate than sleep mode.

Little brown bat (Myotis lucifugus), a species highly impacted in the East. Credit: Cori Lausen/WCS.

For the most part, over the last several million years, bats have evolved and adapted to survive under local environmental conditions, but if a hibernating bat miscalculates its energy expenditure, as we sometimes do with our cellphones, they end up in similar condition — dead.

Scientists think excessive energy use is why some eastern bat species have succumbed by the millions to a fungus that was introduced from Europe into North America a decade or more ago. The fungus causes a disease called white-nose syndrome, or WNS, that alters the energy balance of some hibernating bats by triggering more arousals than normal during winter months.

“On Halloweens of late, it is bats who have had a monster to fear.”

Since the bats are hibernating and cannot recharge mid-winter, they starve. If they can’t hang on (literally) until spring arrives to replenish the energy lost to extra arousals from the disease, they perish.

As a wildlife epidemiologist working for the Wildlife Conservation Society, my mission is to apply lessons learned about this disease in Eastern North America to help protect western bats that have not yet been exposed to the fungus, which is slowly moving west. There are already three bat species listed as endangered in Canada and one in the U.S. because of WNS.

- Distribution and spread of WNS map as of August 2016, adapted from website.

The threat of extinction is real and it carries ecological implications that go beyond the loss of a unique bat species. Bats play a critical role in our natural world, providing services to people such as pollination and insect control. Losing a species to this pathogen would be a tragic — and truly scary — prospect.

Since 2014, I have had the pleasure of leading a dedicated interdisciplinary team of scientists. Our aim is to apply our knowledge about the energy costs of this disease to help identify potential “refugia,” or safe areas, in the West where bats will survive.

This fall we began a four-year research project with $2.5 million in funding from the Strategic Environmental Research and Development Program of the Department of Defense. Our study area is the western U.S., which was pathogen-free until the disease was detected in Washington State this past spring. The project is closely linked to bat sampling and winter ecology research led by Dr. Cori Lausen of WCS Canada, so that collectively our work spans an enormous geography — from Texas to Canada’s Northwest Territories.

Dr. Sarah Olson on a scouting mission for field sites Credit: D. Bobbitt/USFS.

Our project is uniquely pro-active. Many western hibernation sites, known as “hibernacula,” are not protected because we don’t know which populations and species will be susceptible and the importance of specific sites on a population level is unknown. We hope to change that by using information collected from western bats and hibernacula across a wide area under a variety of conditions to identify which bat species and populations may be vulnerable. We can then intervene at the local level with tools to help enhance adult survival, such as building maternity roosts and placing stronger protections on strategic hibernacula.

Last month, standing near a broken band of limestone cliffs midway up a steep mountain foothill, we captured our first bat of the project, a juvenile male long-eared myotis (Myotis evotis). We recorded his measurements, and observed that he was dangerously underweight for this time of year, about five grams or the weight of a nickel. The other bats we caught that night were nearly double in weight.

The information we collect from each bat will steadily grow into a database. In doing so the bats themselves will help us give them every fighting chance to survive the disease. It’s a Halloween story that needn’t have a scary ending. Indeed, for every child frightened by Dracula, there should be one reassured by healthy hibernacula.

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Dr. Sarah Olson is a wildlife epidemiologist with the Wildlife Health Program at WCS (Wildlife Conservation Society).

WCS saves wildlife and wild places worldwide through science, conservation action, education, and inspiring people to value nature.

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