Bat Populations Threatened By Mysterious Fungus

By Nancy K. Crevier

As dusk falls on a summer’s evening, the sky above comes alive with flying creatures. Giant dragonflies and damsel flies skim through the air, making a meal of mosquitoes and other tiny, biting insects. They are not alone in their daunting task, though.

Also flying high in the summer breezes are the bats, nature’s flying mammals that are responsible for making the summer evenings bearable through the millions of pests they devour between the hours of dusk and dawn. It would not be unusual to see dozens of little brown bats flitting on high, their small bulky bodies kept buoyant by paper-thin wings, silhouetted against the darkening sky.

But just when the rain and cool weather this summer have colluded to produce prodigious numbers of mosquitoes and we are most in need of the bat’s ravenous appetite, the Northeast bat population is sinking due to a deadly fungus known as “white nose syndrome (WNS).”

The US Fish and Wildlife Service estimates that between 400,000 and 500,000 bats in nine states have succumbed to WNS since it was first identified in 2006. Connecticut is among those states, along with neighboring states New York, Vermont, New Hampshire, and Massachusetts. Other states with confirmed cases of WNS, which appears to cause bats to lose weight and starve to death during hibernation, are New Jersey, Pennsylvania, Virginia, and West Virginia. WNS was first identified in Connecticut in early 2008.

WNS presents as a white, furry fungus growing on the muzzles of bats, as well as on the wings or other body parts. According to the US Fish and Wildlife Service, the fungus may be an invasive, cold-loving fungus that is spread from direct bat-to-bat contact or from bat-to-cave contact. It is fatal to nearly all bats that contract it.

Connecticut is home to eight species of bats, five of which have shown occurrences of WNS, said Connecticut Department of Environmental Protection (DEP) biologist Jenny Dickson. Little brown bats and Northern bats, also known as the long-eared bat, and the Eastern pipistrelle have suffered the greatest number of losses, with the big brown bat and the endangered Indiana bat also incurring great losses. Other bat species in Connecticut — the silver-haired bat, the red bat, and the hoary bat — seem to have not contracted the fungus so far.

“We are trying to find out if the fungus is the sole cause [of the increased bat deaths] or if something else is affecting the bat population, making them susceptible to the fungus,” Ms Dickson said. “We know that WNS seems to alter their wake and sleep patterns. Every time they wake up during hibernation, they burn more body fat that they cannot spare. What we have seen are bats becoming underweight, and leaving the caves in search of food long before any food is available to them,” she said.

A High Death Rate

In a release issued by the Connecticut Department of Environmental Protection Wildlife Division in March of this year, experts stated that the syndrome had affected bats to a much more severe extent over the winter than had occurred the previous year. Approximately 80 to 90 percent of bats in two of the state’s major hibernaculas (cave and mines where bats hibernate) died due to complications attributed to WNS. A great number of the bats that return to their summer roosts in Newtown each year overwinter in those two large Connecticut hibernaculas, Ms Dickson said, and many others seen locally are from the WNS affected caves in New York. “Bats tend to be loyal to the places where they hibernate and where they roost in the summer, so it would not be unexpected to see the very same bats return each summer to an area. There has been a huge change in the number of bats seen by the casual observer in Newtown and surrounding towns this summer,” she said.

In an effort to determine the effect of WNS on the bat population, in March the Connecticut DEP appealed to state residents to report any changes in bat population observed this summer. “The resident response was good,” Ms Dickson said, “but the new was not good. The vast majority reporting on existing colonies reported lowered numbers.” People watching colonies also reported seeing bat pups falling out of the roosts or finding dead pups in front of the roosts in greater numbers than ever before.

“This is of considerable concern to us,” said Ms Dickson. “It could be somewhat weather related, but the spread and severity for the reports suggests something else is at work, too.” Pups not thriving could be due to the adult bats coming out of hibernation in poor health, she suggested. “We also have to wonder if the adults are passing on a form of the fungus to the young,” she said. Those theories and others are being investigated presently, and dead pups are being tested in Madison, Wis., as researchers seek an answer to the mysteries of WNS.

Controlling Insects

Bats play an important part in the controlling of pesky nighttime flying insects. A single little brown bat can consume between 600 and 1,000 pests in one hour. Not only are humans protected to some degree by the consumption of potentially disease-carrying insects, but forests and gardens are also rid of destructive insects. A reduction of the Connecticut bat population by 80 to 90 percent means that a significant number of mosquitoes and other biting insects are surviving this summer. Bats also play a smaller part in pollination and the spread of seed, as well as serving as prey to larger predators.

There is some sense of urgency to halt the spread of WNS, as the bat population has been depleted significantly. Recovery to former numbers, even at this point, could take decades, Ms Dickson said. “Bats are fairly long-lived, with the males living into their 30s, and they reproduce slowly,” she explained.

While it is unclear exactly how the fungus is spread, this spring the US Fish and Wildlife Service and the National Park Service issued a request to cavers for a voluntary moratorium on caving in any of the WNS affected states, or in adjoining states, at any time. It is suspected that human activity in caves may advance the spread of WNS through contamination of boots and gear used when caving.

“The response from caving societies has been good,” said Ms Dickson.

The Connecticut DEP remains interested in reports from state residents concerning bat populations, she added. To report bat counts or unexplained deaths of bats, call 860-675-8130.