Attack of the Killer Fungus
Will white-nose syndrome spread to Texas bats?
By Wendee Holtcamp
Dusk settles over Austin’s Lady Bird Lake as a few hundred people mill about, talking, waiting and watching the sky. Some peer over the edge of the Congress Avenue Bridge. Others gather on a grassy knoll below. A man juggles to keep people entertained, and others sell glow sticks and snacks to excited kids. A handful of people stand nearby, examining the four-panel educational kiosk. It’s my third visit, but I’m excited by the presence of my friend Doug, a first-timer. Soon, the reason why we have all gathered will become apparent. It’s one of nature’s most beautiful and inspiring spectacles — the nighttime emergence of hundreds of thousands of bats. Bat watching, particularly in Austin, has become an international phenomenon.
But what if all these bats were to vanish?
A mysterious ailment, white-nose syndrome (WNS), has killed more than a million hibernating bats of six species since 2006. Its rapid spread radiated outward from New York, and by the winter of 2008-09, had killed bats in eight other states: Pennsylvania, Vermont, Massachusetts, Connecticut, New Hampshire, New Jersey, Virginia and West Virginia. It has affected one endangered species, the Indiana bat, and imminently threatens three others.
As WNS spreads across the country, Texas must sit and wait, watching a ticking time bomb. It’s “the most precipitous wildlife decline in the past century in North America,” according to a consensus statement by scientists who gathered in Austin in May 2008 to discuss WNS as they prepared for a June 4 presentation to the U.S. Congress to plead for research funds.
Doug and I walk from the grassy knoll up some stairs to the bridge itself, passing by a sign that says “Welcome to the World’s Largest Urban Bat Colony.” We join Bat Conservation International biologist Mylea Bayless. The sky has grown deep blue, and anticipation builds as people keep looking around for the spectacular acrobatic flying mammal night show.
Bayless shares some cool bat facts, including the many benefits that bats provide. I learn that the 100 million Mexican free-tailed bats in Central Texas eat 1,000 tons of insects every night, and the 1.5 million bats at this bridge alone eat 10,000 to 30,000 pounds of insects nightly. Texas boasts 32 of the nation’s 45 bat species, including one federally endangered species. We’re most famous for the Brazilian (or Mexican) free-tailed bats that dine mostly on moths. Scientists value the pest control that bats provide in the South Texas Plains’ eight-county Winter Garden agricultural area at $1.7 million. And then there’s tourism. Austin’s bats attract 100,000 people every year, yielding $10 million in tourism revenue. There are nine other public bat-watching sites statewide. What would happen to Texas bats if WNS strikes here?
The story of WNS started when recreational cavers noticed fuzzy, white muzzles on several bats in Howes Cave outside Albany, N.Y., in February 2006. One snapped a photo but didn’t share it with authorities right away.
The following winter, when bats should have been deep in hibernation, people started observing bats flying about and then showing up dead on neighborhood lawns. The number of bat carcasses sent to health labs increased tenfold. At first, people suspected a rabies outbreak, but the carcasses showed no signs of rabies.
The New York State Department of Environmental Conservation took note of the strange happenings and started investigating in February 2007. What they found shocked them. At one site, Hailes Cave, thousands of bat carcasses littered the cavern floor. In the five caves searched, 81 to 100 percent of the hibernating bats had disappeared, and those still alive had telltale white muzzles. They called the baffling ailment white-nose syndrome.
As bats hibernated in their cool, humid caves, a never-before-seen fungus had started attacking them, invading their skin, wings, ears and other tissue. U.S. Geological Survey scientist David Blehert likens it to food in your refrigerator that has gone moldy. A small percentage of bats survive in WNS-stricken caves, but it’s not certain whether they have immunity or end up dying the next year in hibernation. Some affected bats seem severely underweight compared with healthy bats, but not all infected bats show visible signs of infection.
It seems to be the era of killer fungi. Some have compared WNS to the cool-weather chytrid fungus that emerged in 1999, attacking amphibian populations worldwide. Scientists now partly blame a parasitic fungus for the “colony collapse disorder” that has devastated honeybees. And just this past summer, a new strain of the fungus that caused the Irish potato famine hit the northeast U.S. potato crop hard. In all these situations, scientists continue deciphering just what’s causing such sudden and massive declines.
Blehert and his colleagues isolated and described the fungus on the afflicted bats, which was brand new to science. They named it Geomyces destructans. The discovery brought more questions. Was this an exotic species brought from another country, or did a native fungus mutate? Would it affect other animals, or even people?
“The fungus grows on the bats’ wings and faces almost as if they were Petri dishes. We’ve never seen anything like it among any of the other species of fungi that grow on mammals,” says Daniel Lindner of the U.S. Forest Service, who is collaborating with Blehert on WNS studies. Lindner is trying to find out whether G. destructans grows on cave walls, in soil or just on the bats, and also whether it can be transported on boots or equipment.
“At this point we’re assuming the fungus is an introduced species, since it’s acting like one, but we don’t even know that for sure,” says Lindner. Recently, photos of white muzzles on several European bat species surfaced, but apparently it hasn’t killed those bats. The scientists are in the process of determining whether that fungus is also G. destructans, and preliminary genetic evidence indicates that it is. When species get introduced to a new locale, they can undergo an “ecological release” in which they expand their range, free of competitors, predators or pathogens that keep them in check in their native habitat. Common examples in Texas include red imported fire ants. If G. destructans turns out to be an exotic species, it will have ecological ramifications beyond bats.
Scientists do not know conclusively whether the fungus kills the bats or if lethality is a side effect of another factor weakening their immune systems. Blehert and colleagues looked for — but did not find — any other parasite or pathogen in bats affected by WNS. Also, the fungus seems to invade the skin but not any internal organs, so can that kill a healthy bat? One hypothesis is that the fungal infection causes the bats to rouse from hibernation and deplete critical fat stores, which leads to starvation.
Hibernating bats snuggle in dense aggregations, clearly an ideal scenario for spreading the fungus or any disease, and Blehert’s latest experiments show that the fungus can spread bat-to-bat. But how did it jump from caves in the Northeast all the way to Virginia and West Virginia so quickly? Besides bat-to-bat transmission, another possibility is that people visiting caves might be spreading the fungus.
The U.S. Fish & Wildlife Service and the Forest Service became so alarmed that in spring 2009, they closed several caves across the country and strongly recommended that spelunkers voluntarily suspend activities in caves in affected regions and neighboring states, follow stringent decontamination procedures for gear and not bring gear ever used in affected caves or regions to non-affected regions.
“We recognize that the steps we are recommending will require sacrifice from the caving community and others,” said the USFWS in a March 2009 advisory statement. “However, the observed devastation to bat populations, exceeding 90 percent mortality at many affected sites, and the evidence for human-assisted spread justifies that we exercise an abundance of caution in managing activities that impact caves and bats.”
“Cavers are coming from all over. They could use equipment from the East and could possibly bring WNS out,” says TPWD wildlife biologist John Young, who coordinates the state’s proactive WNS efforts. Since scientists aren’t certain that decontamination even works against these spores, it’s best to err on the side of caution. “Although TPWD doesn’t have a policy right now, we’d recommend people not go into caves where bats are known to occur.”
Young participates in the Western Bat Working Group, which is currently drafting guidelines to best deal with the threat of WNS for western states. He has already started contacting bat researchers and those working at the 10 public bat viewing sites throughout the state, sharing information on what they should look for that may indicate WNS: bats flying in deep winter, underweight bats, scarred and damaged wings and, of course, the telltale — but not always present — white noses.
As we finish talking with Bayless, I hear someone shout, “Look!” and point to a bat flying out from the bridge, and people start chatting excitedly. We look down to see hundreds of bats spiraling under the bridge’s north side. Before long, hundreds and then thousands start flying in a figure eight under the bridge columns, and then out into the sky along the lake, first in one line, then in three or four lines of bats. I’ve now seen bat emergences at three of Texas’ 10 public bat viewing sites, including Clarity Tunnel in the Panhandle and Old Tunnel Wildlife Management Area in the Hill Country, which has freetails plus 3,000 cave myotis.
TPWD bat education specialist Nyta Brown has dozens of fascinating bat facts, but my favorite: the half-million bats from Old Tunnel eat insects weighing the equivalent of 200,000 hamburger patties per night. Freetails prefer moths to mosquitoes, but myotis bats will eat 600 of the blood-suckers per hour.
Scientists have recently determined that G. destructans, the fungus associated with WNS, grows best between 40 and 50 degrees Fahrenheit, and not at all above 68 degrees, so they do not suspect that Texas’ many free-tailed bats are at high risk. Bayless is cautiously optimistic.
“If it is indeed the fungus — and we don’t know that for sure — it does seem to be associated with cold weather environments,” she says. “If southern bats spend less time in hibernation, they may be less susceptible to fungus from WNS.” Bats that hibernate in the Panhandle, including the cave myotis (Myotis velifer) and pallid bat, are vulnerable.
Even if WNS never reaches Texas, declines in bat numbers elsewhere may increase insect abundance in neighboring states, which could cause problems with agriculture here. That, in turn, could affect food prices, especially if farmers compensate with more pesticides. Bats have only a single pup per year and live five to 20 years, so populations in affected regions will recover painstakingly slowly.
“We hope and pray there’s some sort of southern threshold where the damage will be less severe, but we won’t truly know that until we see it come,” says Bayless. It’s a waiting game.
The death of mass numbers of bats will have serious repercussions, especially since they are the only major predator of night-flying insects. As Scott Darling of Vermont’s Fish and Wildlife Department said in his June 4 congressional testimony: “We are at the beginning of a nationwide ecological experiment in which we will find out how one part — bats — affects the whole ecosystem.”
HOW YOU CAN HELP
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Donate to Bat Conservation International’s WNS rapid response fund. www.batcon.org/wnsdonate If you live in the Panhandle, where bats hibernate, and you notice bats flying in winter, report them to the U.S. Fish & Wildlife Service at www.WhiteNoseBats@fws.gov. If you live anywhere in Texas and see dead bats or notice anything unusual, report to TPWD at 512-389-8047. As always, never touch dead or dying bats, but call a wildlife rehabilitator or a rabies lab. Rabies is very rare in bats, but is a serious and deadly disease. Labs can determine the cause of death and will pass along this information to TPWD. Create homes for bats! Bat boxes and roosts are a great way to augment existing populations of bats, which eat pesky insects. Info at BCI: www.batcon.org/bathouse If you’re a spelunker, read and follow the guidelines for decontamination. If you travel, consider renting local equipment rather than bringing your caving gear back to non-affected states. If you’d like to learn more, a list of hibernating and non-hibernating bats is available at www.fort.usgs.gov/WNS. |
