Journey Of Little Brown Bats Tracked By Chemical ‘Fingerprinting’

Little brown bats are tiny creatures that fly through the night hunting insects that humans consider pests, zooming past trees in a wave of sleek brown fur. The 3.4 inch long bats, when not hunting insects in warmer months, hibernate in abandoned mines and caves during the winter.

As peaceful as this image seems, a disease known as white-nose syndrome jeopardizes the little brown bat´s very survival.  A groundbreaking method of tracking the little brown bat by using stable hydrogen isotopes, a chemical “fingerprint” found in organic matter like hair, could help researchers understand the disease better.

Using this method, researchers from Michigan Technological University were able to conclude where the bats choose to spend their summers. This process could aid in tracking white-nose syndrome and help researchers manage the advancement of this deadly disease.

“This novel application of stable hydrogen isotopes can help predict which hibernation sites are likely to exchange bats,” Bump states. “Bat-to-bat contact is believed to be the way white-nose syndrome is spread, so understanding the bats’ movements can help us know which hibernation sites are connected and how disease could potentially be transmitted among locations.”

Joseph Bump, an assistant professor at Michigan Tech’s School of Forest Resources and Environmental Science, and a former undergraduate student in his lab, Alexis Sullivan published their report in July´s issue of the journal Ecological Applications. They studied three colonies of bats that hibernated in three different mines located in the upper western peninsula of Michigan.

Sullivan, Bump, and associates Laura Kruger and Rolf Peterson focused on little brown bats that hibernate in the Caledonia Mine near Ontonagon, Michigan, the Norway Mine in Norway, Michigan, and the Quincy Mine in Hancock, Michigan. Using samples of hair collected from individuals in these three colonies, they searched for the hydrogen “fingerprint” of the water located where the bats grew the fur. Maps have been created by ecologists of different water sources in varying locations, so matching the hair “fingerprint” to the water “fingerprint” can help distinguish the bat´s origin. Until recently, this process was only used in flying birds to track their migratory patterns.

“Relatively little is known about bat-to-bat interactions or how far bats travel between seasonal habitats,” states Sullivan. She explains, “Earlier attempts to use hydrogen isotopes with bats stalled because most hibernating bats don’t make dramatic seasonal migrations, and they have unclear molt patterns, making it difficult to connect their hair to a given habitat.”

Sullivan, lead author of the paper, is currently seeking dual Master of Science degrees in Forest Molecular Genetics and Biotechnology at Michigan Tech and the Swedish University of Agricultural Science. These degrees are part of the ATLANTIS Program, a transatlantic academic program funded by the US Department of Education and the European Union.

In this most recent study, Sullivan, Bump, and their associates were able to, with a 95 percent confidence, project the summer locations of the colonies numbering 23,000 bats in the Norway Mine, tens of thousands in the Quincy Mine, and a probable quarter of a million bats in the Caledonia Mine. Utilizing the stable hydrogen method, the researchers were able to guess the geographic locations of where many of the bats may originate, some as far as 351 miles from their hibernating grounds.

White-nose syndrome has not yet affected northern bats in upper Michigan, as it has in southern bat colonies of the United States where entire populations have nearly been destroyed. It is important to study the little brown bats and how white-nose syndrome spreads, drastically affecting their populations.

Bump explains, “First, they are amazing mammals. Second, we should care about little brown bats because they eat millions of things for which we care much less, like mosquitos.”

This research was funded by the National Park Service Great Lakes Network and the Ecosystems Science Center and the School of Forest Resources and Environmental Science at Michigan Tech.