Deep within a cool and damp cave in Vermont, a stirring commences among tens of thousands of furry, chocolate-brown creatures. These little brown bats, resilient survivors of a devastating fungus that decimated their population, entered a state of hibernation last autumn. Now, in early May, they awaken, disengaging from their roosts on the cave walls and cautiously embarking on their initial flights, in search of the moths, beetles, and flying aquatic insects they rely on for sustenance.
Within the labyrinthine passages that delve into a Vermont mountain, scientists made a significant discovery - one of the first outbreaks of the fungus responsible for white-nose syndrome in North America. The cave floor is strewn with bat bones akin to dry clippings from a lawnmower, with minute skulls concealed amidst the remnants.
However, the plight of the bats persists as they continue to succumb to the effects of white nose syndrome. This syndrome, caused by an invasive fungus initially detected in an upstate New York cave in 2006, lies within a short flight distance from the Dorset, Vermont, bat colony. The fungus rouses the bats from hibernation, propelling them into the wintry air in search of nourishment. Unfortunately, many perish due to exposure or starvation, as the insect population during that time of year cannot adequately sustain them.
The Dorset bats, smaller than a mouse and weighing about as much as three pennies, can be observed skittering across cave walls or huddling together for warmth. Encouragingly, their overall health suggests that certain bat species are adapting to the fungus responsible for the widespread mortality of millions of bats in North America. Alyssa Bennett, a small mammal biologist at the Vermont Department of Fish and Wildlife, emphasizes the significance of this phenomenon, explaining that the bats are primarily surviving in this particular location and subsequently spreading throughout New England during the summer.
Bennett, who has dedicated over a decade to studying bats and white nose syndrome, expresses hope that the Dorset cave serves as a vital source population for the bats' recovery, as she observes the creatures fluttering and swooping around her.
However, the road to recovery will be gradual. Female little brown bats, for instance, give birth to only one pup per year. Additionally, while these bats can live into their teens or 20s, only 60% to 70% of the offspring survive their first 12 months, according to Bennett.
Presently, scientists estimate that the Dorset cave harbors a hibernation site for approximately 70,000 to 90,000 bats, constituting the largest concentration of bats in New England. In comparison to the 1960s, when the location was last surveyed before the white nose syndrome outbreak, the winter population has dramatically declined from an estimated 300,000 to 350,000 or more.
The extent of the decline in bat numbers after the onset of the fungus remains uncertain, but biologists who visited the cave in 2009 or 2010 observed a distressing scene: the ground in front of the cave was covered in dead bats.
The fungus responsible for white nose syndrome is believed to have been introduced to North America from Europe, where bats seem to have developed some resistance to it. Named for the white, fuzzy patches it creates on bats' noses and other body parts, this fungus has decimated 90% or more of bat populations in certain regions of North America.
A recent report by the North American Bat Conservation Alliance revealed that out of the 154 known bat species in the United States, Canada, and Mexico, 81 are facing severe risks due to white nose infection, climate change, and habitat loss.
This situation carries significant importance. According to the U.S. Geological Survey, bats play a crucial role in bolstering U.S. agriculture, contributing an estimated $3.7 billion annually by consuming insects that damage crops, such as moth larvae that bore into corn plants.
For several years, scientists have observed that certain little brown bats have displayed a remarkable ability to survive exposure to the fungus, despite concerns of widespread mortality that could potentially wipe them out. While the little brown bats in Dorset, Vermont, have managed to persist, other once-common species, such as the northern long-eared or tricolored bats, have become incredibly difficult to detect in the area, according to Bennett.
Bennett highlights the uniqueness of the Dorset bats, stating that there is something special about them. Although the exact factors contributing to their survival remain unknown, collaborative genetic research suggests that these bats possess characteristics related to hibernation and immune response, enabling them to tolerate the disease and pass on these traits to their offspring.
White nose syndrome, the disease caused by the fungus, has been detected in 38 states across North America, according to Winifred Frick, chief scientist at Bat Conservation International, who has closely monitored its spread. Each new outbreak serves as a disheartening blow to researchers. Earlier this year, Colorado reported its first cases of infected bats, signaling the continuing expansion of the disease's reach.
Frick expresses a sense of relief as bats are starting to repopulate areas that were once littered with carcasses, even though the recovery is currently only a fraction of the previous numbers. She sees this as a promising glimmer of hope.
Apart from Vermont, other regions near the initial discovery of white nose syndrome also report stable or potentially increasing populations of little brown bats. Pennsylvania, for instance, experienced an estimated loss of 99.9% of its bat population due to white nose syndrome, according to Greg Turner, the state mammal expert for the Pennsylvania Game Commission. Although the numbers remain low, they are gradually on the rise in certain locations. In 2016, an old mine in Blair County had just seven bats, whereas this year the count exceeded 330.
Turner expresses a growing sense of optimism, stating that he feels more confident now. The fear of extinction is no longer looming over them.
Research conducted by Turner reveals that bats hibernating at colder temperatures have a better chance against white nose syndrome because the growth of the fungus is slower in such conditions.
The preference for colder temperatures among bats may indicate a reduced likelihood of waking up due to the irritation caused by the fungus. However, scientists still lack a comprehensive understanding of the underlying mechanisms that enable some bats to survive while many others succumb to white nose syndrome.
According to Turner, by selecting colder temperatures, bats are benefiting in two ways: preserving their fat stores and energy while also experiencing reduced disease prevalence.
Nonetheless, there are concerning trends. Pennsylvania's bat population remains a mere fraction of its pre-white nose levels. In certain areas, Turner and his colleagues have observed an increase in bat numbers, but there is an inexplicable scarcity of female bats.
In Virginia, populations have declined by over 95%. Although the state is witnessing stabilization or slight growth in bat numbers in some colonies, this recovery is limited to a fraction of the sites that were once monitored, as noted by Rick Reynolds, a non-game mammal biologist with the Virginia Department of Wildlife Resources.
The article acknowledges that while there is a sense of optimism, the recovery of bat populations still faces challenges and uncertainties. Rick Reynolds, a non-game mammal biologist with the Virginia Department of Wildlife Resources, emphasizes the long road ahead and the need for continued efforts.
In the Dorset cave in Vermont, where temperatures remain low during winter, the bats have seemingly found a favorable environment that slows the growth of the fungus. Alyssa Bennett, a small mammals biologist for the Vermont Department of Fish and Wildlife, is collaborating with Laura Kloepper, a bioacoustics expert from the University of New Hampshire, to better understand the population count of the bats. They are using acoustic modeling and comparing sound recordings with thermal imaging to estimate the baseline population and track any changes.
Their goal extends beyond saving the local bat species or those in the Dorset cave; they aim to contribute to the conservation of bats worldwide. The researchers are dedicated to understanding the disease and finding ways to protect and preserve bat populations globally.