Photo Credit: Kimberli Miller, USGS National Wildlife Health Center.

Standing in the entrance of a Vermont cave in March 2008, it was clear from the dead bats in the snow, another flying in the frigid cold and one clinging to an icicle that something was wrong.

I’m a Wildlife Disease Specialist for the USGS National Wildlife Health Center in Madison, Wisconsin.  The Center’s mission is to safeguard wildlife and ecosystem health through dynamic partnerships and exceptional science.  I was at the cave with two Vermont Fish and Wildlife Department biologists to learn more about white-nose syndrome (WNS), a new disease that was killing bats in New York, Vermont, Massachusetts, and Connecticut by the thousands.

Bats are fascinating creatures that have evolved very specialized survival skills.  One of these is their ability to hibernate to conserve energy by reducing their heart rate, temperature and other body functions to very low levels for extended periods.  This allows bats to survive long winters using their stored body fat when their insect food source is unavailable.  Although bats may briefly rouse out of hibernation to drink water or move to a different part of the cave, they typically stay deep in their hibernaculum or winter “roost site” until spring.

So it was odd in winter 2007 when New York residents reported seeing bats flying during the day and finding them dead in the snow in their yards.  Biologists following up on the reports were surprised to find a nearby cave littered with dead bats and a fuzzy white growth on the nose and wings of some of the live bats.  The following winter, sick and dead bats were reported in multiple locations in New York as well as Vermont, Massachusetts, and Connecticut.  The disease has now spread as far west as Kentucky, as far south as North Carolina, and to four Canadian provinces.  It is estimated that over a million bats have died since 2007, making this the largest disease outbreak among mammals in modern times.  WNS has spread very rapidly, by bats themselves, and likely also by people moving between affected and unaffected sites.

WNS Occurrence by County. Map courtesy of Cal Butchkoski, Pennsylvania Game Commission.

Navigating the icy rocks into the Vermont cave, dead bats were so numerous; stepping on them was sometimes unavoidable.  A live little brown bat clinging to the rocks overhead didn’t have white nose fuzz but did have wing damage, which we now know, is one of the components of WNS.

Photo Credit: Kimberli Miller, USGS Nation Wildlife Health Center

Nationwide, scientists are collaborating to quickly learn as much as possible about this disease.  One of my Center’s laboratories first isolated a cold-loving fungus from sick bats that they later named Geomyces destructans.  Additional studies determined that it is the cause of WNS.  Other scientists studied the wing damage caused by the fungus and how the injury affects body temperature and hydration during hibernation.  The caving community has helped efforts to prevent the accidental spread of the fungus to new areas on equipment and supplies.  All involved hope to one-day find ways to slow or halt the spread of the disease and reduce bat deaths before WNS causes some bat species to become extinct.

As a hunting bat closes in on a flying insect, its echolocation calls get closer and closer together, and shorter and shorter in duration. The calls, more than 160 per second, give the bat rapid-fire information on the location of its ever-moving prey.

To the human ear, the calls register as one continuous sound. Researchers call it the “terminal buzz,” and until recently, scientists did not fully understand how bats produced it.

Bats use muscles in the larynx to produce sound, just like humans, but scientists had never found a mammal muscle that could turn on and off that quickly.

"You can tap your finger on a table, and you can try to tap your finger as fast as you possibly can," said Andy Mead, a biology graduate student at the University of Pennsylvania. Eventually, your muscles seize up and you can’t tap any faster, Mead said. “You can probably tap five, six, seven times a second if you really try.”

As part of a research team led by Coen Elemans from the University of Southern Denmark , Mead found muscles in a bat larynx that could turn on and off in less than one one-hundredth of a second, firing up to 180 times a second.

"It was instantaneously really shocking and exciting to see yes, this is a very, very fast muscle," Mead said.

The discovery marked the first evidence of a “superfast” muscle in a mammal. Superfast muscles are responsible for the rattle of a rattlesnake and the mating call of the bottom-dwelling toadfish and some songbirds, but the discovery of the muscles in mammals leads researchers to believe they may be more common than they thought. They are also key to the evolutionary success of bats, which are the only flying mammals to use echolocation to hunt.

See the original story from our partners at WHYY.

Additional Links

• Scientific community unites to save bats: Bats are dying at rapid rates of the mysterious white nose syndrome. Learn about efforts in Pennsylvania to study the disease.

The Mexican free-tailed bats living beneath the Yolo Causeway, a three-mile bridge near Davis, make up the largest colony of bats in the Central Valley and most likely one of the biggest in California, said Corky Quirk, education associate with the Yolo Basin Foundation.

Corky Quirk helps QUEST producer Gabriela Quiros prepare to film the bat flyout at the Yolo Causeway.
Photo: Amanda Stupi

The Yolo Causeway carries highway 80 traffic over the Yolo Bypass, a flood-control structure that protects Sacramento, West Sacramento and nearby communities from the Sacramento River’s rising waters during the winter.

The bats fly out from under the bridge each evening from two locations. Between June and August, Quirk takes groups of visitors to watch a large group of the bats fly out in the Yolo Bypass Wildlife Area, which is managed by the state’s Department of Fish and Game. This year’s bat tours sold out after the Sacramento Bee published a story.

Bats fly out over the Yolo Bypass Wildlife Area, in Davis.
Photo: Corky Quirk

But you can watch a slightly smaller group of bats fly out shortly before sunset from the causeway’s bike trail, on the bridge’s west end. Quirk recommends parking on the northwest side of the causeway and walking up onto the levee to reach the bike trail. The bats fly from under the causeway near the levee on the north side.

Scientists don’t know where these bats spend the rest of the year, although they suspect that some of them remain at the causeway and that others live under nearby Central Valley bridges and in the Bay Area. In another QUEST video I produced, bat scientists counted 16,000 Mexican free-tailed bats spending the winter under a small bridge in the town of Galt, 20 miles south of Sacramento.

The bats start to arrive at the causeway in May and make themselves at home in the bridge’s exposition joints, crevices that are one inch wide and 12 inches deep and allow the cement structure to contract and expand.

“In our area we don’t have caves, which would be the normal habitat for this particular species,” said Quirk. “But they’ve adapted to live in the structures that the humans have ended up providing.”

Mexican free-tailed bats have adapted to living under bridges instead of in caves. Photo: Kate Szrom

Mexican free-tailed bats are one of around 16 species of bats in the Bay Area, said Dave Johnston, a wildlife ecologist and an officer of the Western Bat Working Group. While this species is doing well, other Bay Area bats such as the long-eared myotis, the Townsend’s big-eared bat and the pallid bat, aren’t as numerous as they once were.

“What we’re learning is that more and more of these species are more sensitive to urbanization than we previously thought,” said Johnston. “Habitat fragmentation and habitat loss are probably the big suspects.”

And a disease called white-nose syndrome has killed more than one million bats in the eastern United States since it was introduced to New York state in 2006, likely from Europe. The fungal disease attacks bats hibernating in caves and causes them to develop what looks like frost on their snouts and chins.

The disease is expected to reach California, but Johnston said it’s not clear how it might impact the state’s bats.

“Our bats typically do not go into the deep torpor or deep hibernation when this fungus does its worst effect,” said Johnston. “So that’s a wild card out there.”

Adult Mexican free-tailed bats weigh about half an ounce and are three inches long. Their 10-inch wingspan makes them look bigger when they’re flying, which they do at speeds of about 50 miles per hour. Under the causeway, they chatter away in high-pitched, bird-like chirps. But when they exit the bridge at sunset, Quirk holds up a phone-sized machine called a bat detector to hear the high-frequency sounds that help the bats locate their prey. Without the bat detector, these sounds aren’t audible to humans.

In California’s Central Valley, Mexican free-tailed bats feed on the moths and moth larvae that attack corn and tomatoes. In Texas, where they’re also known as Brazilian free-tailed bats, they protect the cotton crops and reduce the cost of pesticides for cotton farmers.

“When they’re pregnant or nursing, they’re going to eat about the equivalent of their weight in insects each night,” said Quirk. “They’re very, very important for our pest control.”

Four-day-old bat pup. Photo: Kate Szrom

Each female gives birth to a single pup once a year. The pups, which are born translucent and furless, are large, compared to their mothers.

“I think of it as a human mother giving birth to a kindergartner,” said Quirk. Around July 1, Quirk starts to look for tiny bat placentas and umbilical cords that have fallen to the ground under the bridge – a sign that the bats have given birth.

Because nursing bats need to eat so many insects, once they give birth they fly in thicker groups than during their pregnancy. They fly out from under the bridge in a long, twirling line that Quirk describes as a “ribbon.” Each night, three or four ribbons are visible from the Yolo Bypass Wildlife Area.

“I like that they’re so different than their reputation,” said Quirk as she watched a flyout in July. “I like that they’re actually very calm animals for the most part, that they’re hunting insects and not interested in us.”

A Mexican free-tailed bat hunts a corn earworm moth.

Using high-speed video equipment that has become affordable for scientists in the past five years, Breuer and Swartz created the movies as a research tool to investigate the flight mechanics of bats. They coax the bats to fly inside wind tunnels using food rewards.

Lesser dog-faced fruit bat.

The videos reveal the intricacies of how bats use their wings.

“One thing we found is that the movements of the wing are extremely complex compared to birds and insects,” said Swartz. “They have many, many joints they can control independently.”

Their complex wings enable bats to make sharp turns that birds can’t manage.

“They don’t necessarily turn fast,” said Swartz, “but they can turn on a dime.”

Bat makes a sharp turn.

Bat wings are also made out of soft skin – which Swartz calls “compliant.” This gives bats yet another advantage over birds and insects.

“If your wing is made of compliant skin,” she said, “then it billows and that gives you extra lift.”

Not all bat wings are the same, though. Mexican free-tailed bats, which are abundant in California’s Central Valley, have stiffer wings than species like the lesser dog-faced fruit bat found in Southeast Asia.

“As we’ve studied the Mexican free-tailed bats, it turns out that their wing motions look very much like birds’,” said Swartz. “The wing stays pretty rigid, even though they have the same joints than the fruit bats.”

Mexican free-tailed bat. Credit: Nick Hristov and Tatjana Hubel, Brown University

Swartz believes the differences in the wing capabilities of Mexican free-tailed bats and lesser dog-faced fruit bats are related to the differences in their diets. The Mexican free-tailed bats eat mainly insects, while the lesser dog-faced fruit bats eat, well, mainly fruit. Fruit-eating bats need to move through their habitat slower than insect-eating bats, Swartz said. And because they’re moving more slowly, it’s harder for them to maintain lift.

“It might be that the animals that need to fly more slowly need the three-dimensional complexity to make up for that,” she said.

Watch more videos from the Swartz and Breuer labs.

Watch QUEST TV's story on Northern California's bats

QUEST on KQED Public Media.

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So we visited zookeeper Andrea Dougall at the Oakland Zoo to learn about their Malayan and Island Flying Fox. Both are a type of fruit bat, and I couldn’t readily see the difference between them. There are many fascinating things that Andrea taught us about these bats that we couldn't fit into our two minute segment (and honestly, this producer wouldn't mind making a half hour special on these critters!). For instance, they have a lot of blood vessels in their wing tissue, so they make excellent thermo-regulators. If the bat is cold, he wraps himself up in his wings so that the heat from his blood vessels can keep him warm. Likewise, when it's hot out the bats flap their wings to cool off.

When Andrea told us that bats are the only mammals that can have sustained flight by flapping their wings, someone said "but what about the flying squirrel?" Nope– they glide.

These bats don't actually swallow the fruit that they eat, instead they chew it into small pieces, push it up against the roof of their mouth to ring out the juice, which they then swallow, and spit out the leftovers. This is something that Andrea reminded me of when I told her I'd like to take one of these cute critters home as a pet… the amount of rotten fruit pulp that you have to pick up is really unappealing. Plus, of course, it would be illegal.

Perhaps the most intriguing thing to me is the simple fact that these animals spend all of their time hanging upside down. I asked Andrea about that too– how is it possible that they wouldn't experience some sort of leg fatigue and let go of their grip? She told me what's in the scientific literature on other kinds of bats (and we're assuming it applies to fruit bats as well). The deal is that the tendon of the muscle that flexes the claw passes through a tough sheath that consists of 19-50 rings, oriented at an angle so that the inside surface is ridged. So there's some ratchet-action going on in the sheath that holds the claw in a grasping position even after the muscle has relaxed, and it's the tension on that tendon from the body weight that holds the ratchet in place. When the bat wants to move, the tension is released and therefore the claw releases its hold. So basically, the clenched position is the "at rest" position, and the releasing of the foot is the part that takes energy.

If you haven't yet, I highly suggest you make a trip over to the Oakland Zoo to see these highly captivating animals for yourself.

Watch the Cool Critters: Fruit Bats television story report online. Also, if you’d like to see close-up photos of these bats, please visit our photo set over on Flickr.

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Bats have been around for about 50 million years and are among the earth's oldest animals: they also are some of the most misunderstood. Because they are nocturnal and strange looking, people have associated bats with evil things for centuries. Nothing could be further from the truth. In fact, bats play a very important role in the economic and environmental health of the world.

In rain forests and deserts, bats are some of the most important pollinators of plants. Without bat pollinators, the wild varieties of many foods we eat: avocados, bananas, cashews, mangoes and peaches couldn't grow.

Fruit eating bats spread seeds as they fly and digest. As natural insect controls, they can't be beat. One bat can eat up to 600 mosquitoes in one hour!

There are nearly 1000 species of bats worldwide, most of which live in tropical regions, like our very own Flying Foxes at The Oakland Zoo. Forty three species live in the US. In fact, almost a quarter of the world's mammals are bats! Bats are the only mammal that can fly and are in a special order called Chiroptera, which means "Hand wing." Bat wings are actually membranes of skin that stretch between their hands and legs. Bats give birth to helpless young and are breast fed milk by their mothers.

The nine Bay Area counties are a veritable haven for bats. To join the ranks of bat-watchers, head to a favorite outdoor spot at sunset anytime between May and October. Visit Sunol Regional Wilderness, Tilden Regional Park, or Foothills Open Space Preserve. Stroll the campuses at Berkeley or Stanford, or the beach at Bolinas, Pescadero, or Fort Funston. Sit beside one of the lakes in San Francisco's Golden Gate Park or find an open spot in downtown Martinez. The shadows you see in flight may be any of 14 species found in the Bay Area–from the ubiquitous little brown, big brown, or Mexican free-tailed bats, to the diminutive western pipistrelles and sparrow-sized hoary bats.

Over the past 150 years, as development has altered the California landscape, bats have faced the loss of roosting sites and the destruction of woodlands and waterways where they feed. Like birds, bats have been devastated by the use of pesticides that kill off their prey, contaminate water sources, and accumulate in their body tissues. Our beneficial friends are in trouble! You can help California bats by putting up bat houses, or joining a conservation group like Bat Conservation International www.batcon.org.

Check out http://flyingfur.typepad.com for more bat blogging.

*Editor's note: This is not to be confused with "Bay Area Bites," KQED's award-winning food and wine blog, which is going strong.

Amy Gotliffe is Conservation Manager at The Oakland Zoo.

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