health & environment: White nose syndrome: A frightening prospect for bats in Washtenaw County
Macabre superstitions have given bats a shuddersome reputation. Dark, ominous, and spooky, they are iconic emblems of Halloween, but according to the United States Fish and Wildlife Service (USFWS) our fears are unfounded. Rather than fear bats we should be afraid for them.
White Nose Syndrome (WNS) — a fatal fungal infection that decimates bat colonies during hibernation — is likely to arrive in Michigan sometime this winter. Although no infected bats have been detected in the state so far, WNS was discovered in Ohio bats earlier this year, less than 150 miles from Washtenaw County. Diseased bats were also found in Ontario, Canada in 2010.
With WNS on our doorstep, the Michigan Department of Natural Resources and Environment (MDNRE) is asking Michigan residents to report any encounters with bats that are showing symptoms of WNS or behaving oddly. Here's what to look for:
- flying in the daytime during winter
- difficulty flying
- white fuzz on the face or wings
- six or more dead or dying bats near a hibernaculum, such as a cave or mine
Observations should be reported online or called in to the MDNRE Wildlife Disease Laboratory at 517-336-5030.
In addition, the human introduction of the G. destructans fungus which causes WNS is well documented and is believed to have initiated the WNS outbreak. Therefore, Michigan residents and visitors are advised stay out of caves, mines, or other caverns where bats may be hibernating to avoid inadvertently transmitting the epidemic. At this time the biosecurity of bat hibernacula is the only feasible control measure, and there are no known safe or effective treatments for WNS.
The USFWS is calling WNS the worst wildlife epidemic in U.S. history. The disease was first discovered in New York in 2006 and quickly spread to nearby states. Since then, the USFWS estimates that close to seven million bats have died.
When WNS invades Michigan, it will cripple bat populations in Washtenaw County and potentially extirpate several species from the state. Unless a cure is found, uncommon or endangered species are at risk of extinction, and even the most common species are in jeopardy.
Michigan is home to nine species of bats, eight of which inhabit Washtenaw County. The big brown bat (Eptesicus fuscus) is the most abundant species in southeast Michigan, where it is commonly observed flapping in the twilight.
As winter approaches, falling temperatures prompt these bats to migrate in search of places to hibernate, like caves, abandoned mines or attics. It appears that the big brown bat’s affinity for warm buildings rather than caves may grant some protection from the disease, since fewer individuals tend to be snuggled together in one place. Perhaps big brown bats will be able to hold on until a cure is found.
On the other hand, researchers fear the little brown bat (Myotis lucifugus) — an abundant species in other parts of Michigan and one of the most common bats in the United States — could suffer a population collapse in less than 20 years, with a high probability of extinction within 65 years. Historically little brown bats tend to hibernate in cave-dwelling colonies with up to half a million other bats, increasing the likelihood of contact with infected individuals.
Fortunately, the latest research offers a glimmer of hope for this species. Little brown bats appear to be changing their social behavior, and the individuals that remain are now often observed roosting alone instead of in dense clusters.
There is also hope that several of types of solitary or non-colonial bats that have smaller populations in Michigan might weather the epidemic. Three species of tree-dwelling vesper bats, the eastern red bat (Lasiurus borealis), the hoary bat (Lasiurus cinereus) and the silver-haired bat (Lasionycteris noctivagans) may be afforded some protection from WNS because they migrate. When cold weather arrives they tend to move on to warmer climates where temperatures are unfavorable for the fungus, and they overwinter in trees or leaf litter rather than caves.
Although migration helps these bats escape WNS, they face other dangers on the journey to and from their winter homes. Scores are killed each year in wind turbines, which are becoming more prevalent as the United States seeks to expand its energy profile.
Tragically, the advent of WNS means the future is now even more uncertain for Michigan’s four imperiled bat species. One species, the northern long-eared bat (Myotis septentrionalis), is currently being considered for protection under the Endangered Species Act. Northern-long eared bats are not uncommon in the northeastern United States, but they are at risk due to habitat loss and because a large portion of the population overwinters in caves, sharing the space with potentially infected bats of other species.
Two other Michigan rarities, the evening bat (Nycticeius humeralis) and the eastern pipistrelle (Perimyotis subflavus, also called the tri-colored bat), may actually be better equipped to weather the WNS epidemic than our most common bats. Evening bats are a threatened species in Michigan, and eastern pipistrelles do not occur in Washtenaw County but are species of special concern in the state.
Both of these bats hibernate alone or in small colonies and are widespread in the southern United States, increasing the probability that they will survive the WNS outbreak. What’s more, the latest evidence suggests that even in regions hard hit by WNS the numbers of migratory, tree-dwelling bats have begun to rebound. Still, Michigan could lose evening bats and eastern pipistrelles simply because their statewide populations are miniscule.
The most critically imperiled bat species in our area is likely the Indiana bat (Myotis sodalis). It is currently the only endangered mammal in Washtenaw county, and as WNS advances, these bats will probably disappear.
In the past 35 years the Indiana bat population has declined by half due to habitat loss, pesticides, and human disruption of bat colonies during hibernation. Less than 400,000 individuals are left.
As winter approaches almost the entire remaining population of Indiana bats consolidates into just a few caves, where they huddle together by the thousands for warmth. Inside their hibernacula, cool, stable temperatures and high humidity provide the necessary conditions for Indiana bats to maintain their fat reserves until spring. Unfortunately the G. destructans fungus also thrives in this cave microclimate, so after decades of research and conservation, WNS threatens to unravel the Indiana bat’s recovery.
WNS is considered such a serious epidemic primarily because bat populations tend not to fluctuate over time and cannot quickly rebound from a catastrophic loss. Unlike most other small animals, like birds or rodents, bats have very low reproductive rates and are long lived. They typically produce just one pup a year, sometimes two, and many live 15-25 years or more, so population growth is very slow.
All bats are warm-blooded mammals with high metabolisms, so when freezing temperatures set in and insects disappear, they must either migrate to a warmer climate or hibernate. Bats that remain in parts of the country with long, bitter winters require long periods of uninterrupted torpor — a lowered metabolic state that conserves energy by lowering the body temperature to match the ambient temperature of the surrounding air and slowing the breathing and heart rate.
Healthy bats will rouse from their torpor for a few hours every three weeks or so, consuming close to 90 percent of their stored fat by spring. They cannot afford for this cycle to be disrupted. Bats irritated by WNS die because they are aroused much more frequently, and they exhaust their critical fat stores.
There is still a great deal to learn about WNS, and researchers only recently pinpointed the G. destructans fungus from Europe as the cause of the outbreak. The exotic soil fungus, to which Europe’s bats have evolved some immunity, is believed to have been introduced to the United States on the boot soles of a tourist who had visited caves. Once a cave becomes contaminated, 80-100 percent of the population usually disappears within two years.
Though research has also proven that WNS is extremely contagious and nearly always fatal for bats, it does not affect humans. Infected bats can appear to be covered in a white fuzz, growing on the muzzle, wings and ears. However, any bat observed flying during the winter is suspect, since healthy bats are rarely observed outside their winter roosts during hibernation.
So far, there is no cure for WNS, and researchers are focusing on prevention and treatment. Antifungals like those used in athlete’s foot do appear to inhibit the fungus, but these drugs have never been used to “clean” the environment and can harm other species.
Whether or not bats are darling or hideous is up for debate, but many common notions about their ghastliness are patently false, stemming from two pervasive urban legends. The first: that bats are blind, bumbling, flying rodents with a penchant for entangling themselves in ladies’ hair, and the second: that bats are filthy, rabid vermin eager to nip your neck and suck your blood.
In fact, bats are not rodents, but the only true flying mammals, and they make up a quarter of all mammal species on the planet. They are not clumsy, nor are they blind, and there are no documented accounts of bats in hair.
In fact, bats rarely collide with obstacles, and they use echolocation to expertly locate and gobble up tons of pesky insects each evening. For this reason the widespread demise of bats could have steep consequences. According to biologists at the Pennsylvania Game Commission, one million bats eat about 694 tons of insects every year, including crop pests and mosquitoes, and losing seven million of them to date could lead to increased pesticide use or the spread of West Nile virus.
As for their vampiric tendencies, although blood-drinking bats do exist, they do not live in North America. While bats can be a vector for rabies, less than one half of 1 percent are infected, and very few rabid bats are reported in Washtenaw county each year. Still, bat — especially dead bats — should not be handled.
The WNS epidemic, the rise of wind power, pesticide use, and habitat loss are threatening bats, and they need our help. If you see bats behaving oddly this winter, be sure to report the sighting so that it can be investigated.
Since not everyone is keen on sharing their attic, bat removal specialists can safely exclude them, but this should only be done when they are not nursing young or hibernating. If you choose to exclude bats from your home or just want to attract nature’s bug zappers to your garden, installing a bat house can provide a secure, alternative summer dwelling.
For details on building your own bat house and more information about Michigan’s bats, check out the Organization for Bat Conservation website, or see their bats up close at the Bat Zone at the Cranbrook Institute of Sciences in Bloomfield Hills.
Another way to help bats is by supporting campaigns and organizations that fund efforts to combat WNS and protect bats and their natural habitats. The Center for Biological Diversity has information on current legal initiatives, including the Wildlife Disease Emergency Act, and Bat Conservation International funds research and protection here and abroad.
We should fear for our bats as they are considered a “keystone species,” meaning that they are an integral part of the ecosystem that other plants and animals depend on. What will happen when this keystone crumbles? For the endangered Indiana bat, already placed on the brink of extinction by human activities, it may already be too late, and lamentably with the coming of WNS we may soon find out.