Bat Monitoring

Dr. Corinne Diggins sets up an acoustic bat monitoring station. [Photo courtesy USGS]

Add field research to the long list of activities delayed or modified because of the coronavirus pandemic.

Dr. Corinne Diggins of Virginia Tech is gathering data on an important but sometimes overlooked species in the Southeast Utah Group of National Parks: bats. After installing monitoring stations throughout Arches and Canyonlands last summer, Diggins had been planning to return to collect a round of data this past month. However, travel restrictions and park closures have caused her to postpone revisiting the stations.

Bats are our friends

The pandemic that threatens our human communities has superseded other concerns, but Diggins’ research is not trivial. Bats across the United States are threatened by White Nose Syndrome (WNS), a condition caused by a fungus that causes high mortality rates in bat populations.

“Bats play a pretty key role in the ecosystem,” said Diggins. “The majority of bats that we have in the U.S. are insectivore bats. So they fly around and they catch insects on the wing, and they eat a lot of insects.”

She said a colony of 1,000 little brown bats will eat over a ton of insects during one summer. That includes mosquitoes, which are not only annoying, but can be a vector for human diseases.

Diggins said a single bat “can eat more than their weight in insects per night.”

Many of those insects are also potential pests in forests and on farms. A healthy bat population can save farmers and forest managers billions of dollars in pest control measures, and preclude the need for potentially harmful pesticides. Herbivorous bats can also serve as pollinators, though currently White Nose Syndrome is only known to affect insectivore, cave-dwelling bats.

What is White Nose Syndrome?

White Nose Syndrome is caused by a fungus called Pseudogymnoascus destructans, or “Pd,” a non-native species that researchers think may have been transported to the U.S. from somewhere in Europe. Pd thrives in the cool, damp cave systems where many bat species like to hibernate in the winter.

“What we see is the fungus actively invades the living skin tissues of the bat when they’re hibernating,” explained Diggins. During hibernation, bats drop their body temperatures to within just a few degrees of the cave’s temperature, typically around 50 degrees. Their metabolic processes slow down, including their immune systems. But when Pd starts to establish in the bats’ living tissue, they wake up out of hibernation to groom it away.

“If you think about athlete’s foot, it’s a fungus that grows into the dead tissues on somebody’s foot,” Diggins said. “And the one thing you hear about athlete’s foot is it’s extremely itchy. If you think about a fungus that’s growing into your living tissue, that would probably be pretty terrible.”

The fungus itself doesn’t directly kill the bats, but disturbing hibernation is very stressful on an animal. All their bodily systems must operate on whatever energy stores they’ve collected during the preceding summer and fall; if those stores are depleted too quickly, they won’t have enough energy to live through the winter and replenish themselves in the spring.

“The jury’s still out on what exactly causes their mortality, but most people think it's because they’re using up a lot of their resources that they otherwise would be using during hibernation,” said Diggins.

The direct cause of death may be another illness, starvation or predation because the bats aren’t healthy enough to fight off disease, hunt or flee. Even bats that aren’t killed because of depleted resources may have another problem: they aren’t healthy enough to reproduce. Diggins said that while little brown bats in healthy environments can live for over 30 years, they reproduce slowly, producing only one or two young, or “pups,” per year.

“Recovering populations from White Nose Syndrome is going to be pretty slow going—and there might be populations that just don’t really rebound, or take a really long time to rebound,” said Diggins.

Spreading across the country

White Nose Syndrome was first discovered in the United States in a cave in New York in 2006. Since then, it has spread along the whole eastern US, causing population declines from 40-90%, depending on the species of bat.

“You might have had a cave with 100,000 bats in it, and you come back a year or two after White Nose Syndrome hits, and you can barely find a couple hundred bats,” said Diggins.

So far, White Nose Syndrome has spread primarily in the east, primarily through bats switching caves or migrating. But in 2016, White Nose Syndrome was found in Washington State. While some bats do migrate, the distance between known infected areas in the east and the newer infected areas in Washington rule out migration as the mechanism of spread.

It’s not known precisely how the fungus moved, but it seems certain that it was through human activity. One way people can help limit the spread of White Nose Syndrome is by staying out of caves.

Recently, Pd has been found in areas in the southwest, in El Malpais National Monument and Grand Canyon National Park. The presence of the fungus does not mean that White Nose Syndrome is spreading in the southwestern region, but it might be on the horizon. A Dec. 4, 2019 press release from Grand Canyon National Park said a bat captured and sampled in the spring of that year during routine surveillance may have been carrying the fungus.

“The bat did not show any signs of WNS, and the disease has not been detected in bats at Grand Canyon,” the release said.

Additional sampling of bats later that year did not turn up any more evidence of Pd, but it is more likely to be found during the winter. It is also more likely to be found after it has had a year or two to establish.

Grand Canyon National Park protects its12 hibernating bat species by keeping caves closed to the public. (The park is also home to 10 other species of bats which do not hibernate.) The Dec. 4 press release said park staff will increase their monitoring efforts to detect Pd.

There is a possibility that Pd will not thrive as well in the arid southwest as it has proven to do in the more humid climates of the eastern U.S. and Washington State. However, cave ecosystems share common attributes wherever they are located.

“In hibernacula for small bats that have been documented, the humidity and temperatures are generally considered favorable for fungal growth,” said Kimberly Asmus Hersey, mammal conservation coordinator for the Utah Division of Wildlife. “Research is ongoing and, unfortunately, only time will tell how bats of various species are affected by White Nose Syndrome in Utah.”

“It’s a wait-and-see question,” agreed Diggins.

Data collection

While only time will tell if a dry climate will help repress the fungus, Diggins has designed a data collection project to help parks learn about their bat populations before White Nose Syndrome potentially spreads through the region. The project is funded by the National Park Service, and Diggins is doing most of the work herself. She has set up acoustic monitoring stations throughout the parks to find out what kinds of bats, and how many, are living in the parks.

“What we’re trying to figure out is bat species distribution and activity patterns throughout the year, to get baseline data to figure out what the bat community is like before White Nose Syndrome hits the area,” Diggins explained.

The stations consist of an acoustic bat detector hooked up to a solar-charged battery. A microphone is mounted on a pole, 4-6 feet in the air, and it records bat squeaks 365 nights of the year. Diggins selected monitoring sites in different habitat types and at different elevations while locating them close to a water source, where animal activity is more likely. The sites are deliberately far-ranging, and some must be accessed by boat or via rough, four-wheel drive roads.

“It’s quite an effort to get out to all the sites, actually,” said Diggins, who partnered with National Park staff to reach the more remote locations. “It takes about a month or five weeks.”

She started in Capitol Reef National Park and has already collected a year’s worth of data there. She’ll keep those monitoring stations in operation for 2 more years. This past summer, she added sites in Arches, Canyonlands, Natural Bridges, and Hovenweep, and she will collect 2 years’ worth of data in those locations.

A variety of agencies have been monitoring bats in the southwest for many years.

“Some data points are nearly 100 years old,” said Asmus Hersey, naming the Department of Wildlife Resources, the Forest Service, the Bureau of Land Management, National Parks, Universities, and the Utah Division of Oil, Gas, and Mining as agencies that have conducted some version of bat studies.

However, Diggins’ study is in one way more narrow, focused specifically on bat populations in the parks, and is also more broad, logging widespread bat activity over a long period of time.

“This is the first large-scale, multi-year, year-round acoustic monitoring system that’s been put in at any of those parks,” said Diggins. “Our goal is to just start monitoring, hopefully before White Nose Syndrome hits the area, and that way we can understand what those bat populations look like before White Nose Syndrome.”

The coronavirus pandemic has caused a change in schedule for Diggins, delaying her planned retrieval of the first few months of data.

“The detectors have 128 gigabytes of data cards, so I am not worried about them getting filled up data-wise,” Diggins said of the monitoring stations. “But you can have malfunctions so it is good to check them regularly.”

For many of the sites, the detectors have not been checked at all since they were installed, so making sure they’re actually recording is important as the weather warms up and bat activity increases. However, Diggins will have to wait, and she’s at peace with that.

“Obviously, the current situation our nation is in is quite unprecedented, so I just have to go with the flow on this,” she said, venturing to hope that she may be able to check the sites in late summer or early fall of this year.