, October 17, 2011
Unrelated to Harry Potter, Halloween or curse mongering of the Middle Ages, bats are suffering. These important mammals may seem too petite to some to attract widespread attention, but if they die out, the planet could be faced with major insect infestations, among other concerns.
Descended from species in existence 50 million years ago, bats – or Chiroptera – are the primary predators of night-flying insects, consuming large numbers of moths and beetles. Insect-eating bats are crucial to a healthy ecosystem. Significant populations of bats dying out could result in the natural balance being thrown off for many years to come.
Among the 25 species of bats that hibernate across North America, 4 species and subspecies are federally listed as endangered and an additional 13 are federal species of concern. Now add to the equation a newly discovered cold-loving fungus, Geomyces destructans (Gd), which threatens to eradicate them.
Origins
In February 2006, a caver photographed hibernating bats in Howes Cave, located in Schoharie Co., New York, about 40 miles west of Albany. He noticed an unusual white substance on bat muzzles, as well as several dead bats. The following winter, bats behaving erratically, bats with white noses, and a few hundred dead bats in several caves came to the attention of New York Department of Environmental Conservation biologists. In 2007, White-Nose Syndrome (WNS) became the officially designated name for the affliction.
Little brown bats with White Nose Syndrome (WNS). Credit: Nancy Heaslip, New York Department of Environmental Conservation
More than a million hibernating bats have since died. “If you were pondering a perfect storm on cave bats, the nastiest catalysts would be organisms that could exist and strike in the dark, cold and wet environments where bats hibernate,” explained Greg Turner,Pennsylvania Game Commission (PGC) biologist. “Their vulnerability then is unparalleled, because their immune system is shut down to conserve energy. Gd has found this opening. Now it’s up to bats to find a defense.”
Bat Wing Membranes
But combating the fungus could prove quite challenging. A bat’s wing membranes consist of two layers of epithelium separated by a thin layer of blood and lymphatic vessels, delicate nerves, muscles and specialized connective tissues. Healthy wing membranes are critical for maintaining water balance in bats.
Fungus ravaged bat at Glen Lyon Mine. Source: Pennsylvania Game Commission
During hibernation, bats are especially susceptible to dehydration. The exposed wing membranes and large lungs of bats predispose them to evaporative water loss (EWL), and losses from the skin alone can account for as much as 99% of total water loss in healthy hibernating bats.
Dehydrated, or with low body fat, the immune system cannot always fight off a fungal infection. If a bat moves to a colder part of the hibernacula, it becomes further exposed to the fungus.
Gd irritates the deep-sleeping bats, clustered tightly like sardines to conserve energy. Disturbed from their hibernation stupor, the bats get confused and may fly out over the winter landscape looking for food that isn’t there. Death often follows.
Wildlife Support
Map of affected areas (click to enlarge). Credit: US Fish & Wildlife Service
As biologists and other scientists continue to research Gd round the clock throughout the year to look for possible solutions, action plans have been executed for Mammoth Cave, Georgia, Alabama, Michigan, New Mexico, the Carolinas and other locations including Canada to limit human traffic into hibernation zones.
Closing caves and mines to protect the bats prevents the spread of the fungus that can get on shoes, backpacks, hats and outerwear.
The bad news about exotic wildlife pathogens is that when they emerge they rarely can be extricated.
The Good News
Although WNS has spread 1,000 miles inland from where it originated, not all bats seem to be affected. No migrating bats (red, hoary, silver, etc.) have been found with the fungus. Some colonies of big-eared bats living in the same caves as affected little brown bats have not been infected. This may be because they hibernate in a slightly warmer part of a cave. Some European bats have also been found with the fungus but do not seem to be harmed.
Bats with temperature-sensitive radio transmitters, Shindle Iron Mine, Pennsylvania. Credit: Greg Turner, Pennsylvania Game Commission
Monitoring tools are now used to study behaviors of affected bats during winter in caves where they hibernate, investigating physiological consequences of fungal infection in bats, developing a web-based tracking system to assist with the response and investigation, modeling the potential for the disease to spread, and moving toward development of field techniques for conducting WNS epidemiological studies in wild populations of bats.
“As the populations of affected bat species decline, the distribution of survivors will likely shrink to core populations and habitats, creating new management challenges in identification, protection and potential recovery of survivors and habitats,” noted Cal Butchkoski, PGC.
“For our bats, since no treatments are on the horizon, we must fall back to conservative management. As colonies decline, no number will be too small to protect and manage.” Let us hope the bats have a few yet unknown tricks of their own to survive.
COMMENTS