January-February 2019

Photo © Deborah J. Springer

Pseudogymnoascus destructions infection on a bat.

Bat Killer

White-nose syndrome may cause 'the most precipitous wildlife collapse of the past century.'

By Russell A. Graves

Melissa Meierhofer’s life is in a ditch … literally.

As a doctoral student in wildlife and fisheries at Texas A&M University and a research associate with the school’s Institute of Renewable Natural Resources, Meierhofer spends much of her professional life down in culverts in search of bats. 

“It’s my job to go places where people report seeing bats to investigate where they hibernate and why they choose that location,” she explains. These days she’s working with urgency as the invasive fungus known to cause white-nose syndrome, a devastating disease in bats, has invaded Texas bat colonies.

Meierhofer’s leading a multiyear, statewide research study of winter bat hibernacula (places to hibernate) as part of TPWD’s efforts to prepare for the arrival of white-nose syndrome. In Texas, hibernacula can be anywhere bats can squeeze in and sleep through the winter. In the Hill Country’s karst areas, soft limestone forms numerous caves and houses many bat colonies. East of Interstate 35, where Meierhofer does much of her research and caves are all but nonexistent, bats find hangouts where they can: in culverts, under bridges and in other nondescript crevices.

“We’re recording structural characteristics of the hibernaculum to better understand why bats use various structures to overwinter,” Meierhofer says. “We look at things like how long and wide the culvert is and what species of bats are present. We want to understand why bats are choosing certain areas and not others.”

The data may help provide connections between the over-wintering habits of Texas bats and their susceptibility to the spread of white-nose fungus, Pseudogymnoascus destructans (Pd), a cold-adapted fungus that’s killed millions of hibernating bats in North America.

Photo © Kathy Adams Clark / KAC Productions

The fungus that causes white-nose syndrome was found on a Mexican free-tailed bat in Texas in 2018.

The genesis of a killer

“As the agency in charge of managing our wildlife resources, we’re very concerned about the potential impact of white-nose syndrome on our bats,” says state mammalogist Jonah Evans. 

He’s worried for good reason. No one knows for sure how the Old World fungus made its way here from Europe, where bats seem unaffected by it. But one day, a bit of that deadly organism, perhaps just a spot on a spelunker’s shoe, made the leap over the Atlantic and wreaked havoc on North American bats, creatures with no ability to combat the fungus. When first discovered in 2006 in a colony of bats in upstate New York, Pd proved to be especially deadly. 

A bat contracts the fungus either from the cave walls and ceiling or from contact with other bats. The fungus thrives in the cold, infecting the hibernating colony, while the inhabitants’ immune systems are compromised by their slowed metabolisms. The white growth (which congregates around the bat’s snout — hence the name) irritates the bat’s skin, causing infection. This rouses bats from hibernation, causing early and increased use of their stored fat. In cold places, where bats hibernate longer, the affected bats either starve or emerge in search of food and die from exposure.

Bat colonies are collapsing from white-nose syndrome at an alarming rate. In northern bat colonies, sites that were once home to thousands of bats are down to only a few survivors.

For some bat species, the disease is especially devastating, resulting in massive die-offs. A study in the journal Science predicts that the little brown bat — once one of the most common bat species in North America — may go extinct in the eastern United States within 16 years. Ninety percent of northern long-eared bats are gone; the species is facing extinction.

According to Bat Conservation International, a national nonprofit conservation group headquartered in Austin, northern long-eared bats disappear from their winter homes within just a few years of the fungus showing up, which could make white-nose syndrome the cause of “the most precipitous wildlife collapse of the past century.”

Gone to Texas

Currently, white-nose syndrome has been found in 33 states and seven Canadian provinces. In the past few years, the fungus that causes the disease made its way into three states that scientists considered the far edge of the cold-weather fungi’s range. One of those states is Texas.

“Texas has the highest number of bats of any state in the country. That’s why we’re especially concerned,” Evans says. “As many as 11 Texas species may be impacted by the disease.”

Through monitoring efforts, scientists knew the fungus was spreading west. From western Oklahoma, Pd fungus jumped the state line and was first documented in the eastern Texas Panhandle in 2017. Cave and bat samples collected from Childress, Collingsworth, Cottle, Hardeman, King and Scurry counties all tested positive for Pd in three species: tricolored, cave myotis and Townsend’s big-eared bats. In the spring of 2018, the fungus made its way to Central Texas (Blanco and Kendall counties) and onto a Mexican free-tailed bat.

While the fungus has been detected in 10 Texas counties, Evans says, no signs of the white-nose syndrome disease have been observed. With our warmer winters, many bats either don’t hibernate or don’t hibernate as long, and it is hoped that they will be less susceptible to the cold-loving fungus.

“It remains to be seen if white-nose syndrome will have the same serious impacts in Texas as it has in northern states,” Evans says. “Nineteen species of bats in Texas do not regularly hibernate, so we are hopeful they will not suffer significant population declines.”

The Mexican free-tailed bats that congregate in large numbers in Texas are primarily migratory. While nobody knows for sure, researchers hope that white-nose syndrome will not cause high levels of mortality in this species.

The Texas Parks and Wildlife Department is working hard on white-nose syndrome, funding close to a million dollars of research and monitoring projects across the state in the last six or seven years.

“Our focus is to watch the virus closely and try to determine the ways we can reduce its impact on our bats,” Evans says.

Photo © Dan Lindner / USDA Forest Service

A culture of the fungus Pseudogymnoascus destructans is grown in a lab

The big deal about bats

Historically, bats are a maligned species. As far as mammals go, they aren’t as charismatic as white-tailed deer or bobcats. Horror films depict them as harbingers of evil, and some people malign them as active carriers of rabies. Because of that bad reputation, it’s potentially harder to build public support when they start to disappear.

But many agricultural products from corn to tequila are dependent on pollination, so bats are important to us. People are starting to learn more about these tiny mammals and fear them less.

How we feel about bats, says BCI’s Mylea Bayless, is starting to change for the better.

“I think the public perception is shifting,” Bayless says. “There was a time when bats got a bad rap. I think we have a kinder, gentler and more educated public these days, and they tend to be more curious about the surrounding world than maybe they used to be. Bats are receiving a lot of attention both as an underdog in the case of white-nose syndrome and as a hero for the positive impact they have on our ecosystem.”

The value of ecological services by bats to agriculture (reduced crop loss from insect pests, reduced spread of crop diseases and reduced need for pesticide application) is $1.4 billion annually in Texas. Nationally, that number jumps substantially as bats consume nearly 700 tons of insects annually, saving the nation’s farmers nearly $23 billion from crop losses while they spend nearly $4 billion less on pesticides. Ultimately, consumers save money at the checkout line, all because of bats.

“Bats matter for lots of reasons,” Bayless says. “They’re incredibly diverse as a group of mammals and have a wonderful place in the ecosystem. They provide a ton of ecological services to people and throughout our agricultural communities.”

While some research is showing promise for treating the fungus and white-nose syndrome, a sure-fire solution has yet to be discovered. Evans hopes, for the bat’s sake, that an answer is found soon. Biologically, bats don’t have the capacity for fast-paced reproduction to recover from a disease outbreak.

“Bats are really slow to rebuild their populations,” Evans says, comparing the reproductive rates of bats to larger mammals like black bears or mountain lions. At least a couple of bat species are likely to be listed as threatened or endangered species soon.

“This is the biggest threat to bats that has happened in my lifetime,” Evans cautions. “White-nose syndrome is a big deal.”

Russell Graves is a professional photographer and writer who specializes in wildlife, hunting, fishing and agriculture.