Since 2007, when scientists began reporting a massive die-off of hibernating bats in Northeastern United States, biologists have been scrambling to understand the epidemic and to stop it before it wipes out entire bat species. In just a few years, a body of knowledge has formed around the disease, although the exact cause and cure are still not known.
A lover of bats since he was a child, Adam Eichenwald ’14 is using his final year at Bowdoin to investigate some of the puzzles surrounding the disease, which is known as white-nose syndrome for the white Geomyces destructans fungus found on the muzzles and wings of stricken bats. For his senior-year honors project, Eichenwald has been researching the effects of the syndrome on bats that are not susceptible to the fungus. These tend to be bats that can migrate or hibernate, and when they do hibernate over winter, do so in trees or leaf litter rather than in caves.
What is known about white-nose syndrome is that it develops in hibernating bats in winter, when the mammals are holed up in cool, moist caves. While the exact cause of death of infected bats is unclear, one theory has it that the fungal growth irritates the bats, rousing them from hibernation. “Waking consumes energy,” Eichenwald said, and the bats have just enough energy stores to survive winter.
In a recent talk he made to Bowdoin biology faculty and students, Eichenwald said he is approaching the environmental mystery from a new angle. He wonders whether the widespread death of cave-hibernating bats could be boosting the numbers of non-cave dwelling bats. This ecological see-saw is known as competitive release. If two species in a shared habitat are in competition over a limited food source — for bats, this would be insects — a decline in one species would increase the numbers of the other. “Competitive release occurs in the absence of the competing species,” Eichenwald said.
Eichenwald has narrowed his research to the bats in Maine’s Acadia National Park, in Mount Desert Island. The park first noted white-nose syndrome in 2012, releasing a press release explaining that the loss of bats in Maine could lead to unhealthy ecosystems. “Bats are…tremendously important in managing mosquitoes and other biting insects. Losing even a small percentage of Maine’s bats could have a devastating effect on one of nature’s ecological controls of forest and wetland insects,” the park warned.
Eichenwald contacted the park and got permission to do research there. Starting last April and continuing through October — with financial support from Bowdoin’s Henry L. and Grace Doherty Coastal Studies Research Fellowship and the Peter J. Grua and Mary G. O’Connell Research Award — Eichenwald set up recording devices in trees in two park locations. With these turned on throughout the night, he captured the echolocation calls made by hunting bats. These recordings consist mainly of calls from the park’s two most abundant bat species, the cave-hibernating Little Brown bat and the tree-roosting Eastern Red bat. Eichenwald also had access to acoustic records taken by Maine bat biologist Tim Divoll, who has been researching bats in Acadia Park bats for several years.
In 2010, the echolocation calls of Little Brown bats dominated the recordings. But by 2013, the acoustic record showed a notable decline of Little Brown echolocation calls, instead picking up more calls by Eastern Red bats. Eichenwald noted that the Little Browns dropped off by a factor of 10, while the Easten Reds increased by the same proportion — a favorable sign his hypothesis of competitive release was correct.
However, to argue that these two events are related, Eichenwald has to show that the two bat species compete with one another in the same ecological niche. To do this, Eichenwald has been analyzing three-years worth of fecal samples that Divoll has collected from park bats. The same insect DNA should show up in both the droppings of Little Brown bats and Eastern Red bats. Conclusive results from these tests won’t be ready for a month or so, Eichenwald said.
If Eichenwald’s theory proves solid, it could mean a glimmer of hope. “White-nose syndrome, while terrible for cave bats, could be beneficial for tree-roosting bats and other bats that are not affected,” he said. Going further, if his research findings are corroborated by other scientists, Eichenwald hopes his information could lead to better protections for Eastern Red bats — to safeguard the bats that do remain.