Wyoming’s Mysterious High Country Bats Focus Of 3-Year Census

A three-year bat census is in the homestretch to study Wyoming’s high country flying mammals. Bats are important to Wyoming -- just one brown bat can eat 1,200 insects in an hour. They also pollinate more than 300 species of fruit and even more flowers.

AS
Amber Steinmetz

July 07, 202410 min read

A small colony of Townsend's big-eared bats, one of the 18 species found in Wyoming.
A small colony of Townsend's big-eared bats, one of the 18 species found in Wyoming. (National Park Service)

There are 18 species of bats in Wyoming, 11 of which are considered of “greatest conservation need,” which means state and federal wildlife officials lack basic information relating to just how many bats there are or where they’re living.

For a lot of people, the less known about those creepy flying critters the better. But that’s not how animals — no matter the stigma and revulsion associated with them — are effectively managed.

With a lot of information about bats in the Cowboy State remaining a mystery, it makes dealing with them more challenging. To help, Draper Natural History Museum Curator Corey Anco of Cody, along with three other researchers, launched the Absaroka Bat Census in 2022.

“There's a lot of work being done on elk migration, pronghorn, wolves and bears,” Anco said. “So, when we think about where we can make the most significant impact, it's an understudied species in an understudied system.”

They’re Insect Vacuums

Bats provide a variety of importation ecosystem services including pest control, pollination and seed dispersal.

Just one brown bat can eat 1,200 insects in an hour. Bats are also important pollinators, pollinating more than 300 species of fruit and even more flowers.

The goal of the bat census is to discover bat occupancy and diversity in high country areas that are challenging to survey. The three-year study is entering its final year this summer and the team is continuing to push through challenges to better tell the only full-flighted mammal’s story.

“The rugged topography and landscape make it really difficult,” Anco said. “Plus, the equipment is heavy, and you often need many people or a team of horses to haul the gear up there.

“And it's a big time commitment, because you're recovering that gear every four to seven nights and trying to move it to another location. It’s a lot of work for what started as an unknown, but we're making a positive impact.”

How High Do Bats Live?

In the first year of the study the team wanted to determine if it was even possible for bats to live at higher elevations above the tree line. So the group headed to the high country with the aim of recording bat sounds to identify the types that live there.

For the bat census, Anco is joined by Jason Riggio, a postdoctoral scholar in the Department of Wildlife, Fish and Conservation Biology at the University of California-Davis, research bat biologist Katy Goodwin and ecologist Jordan Harrison.

“There was anecdotal evidence of people saying they had seen bats about the tree line while camping, but there had been no formal study done, so nothing conclusive,” Riggio said. “So the first question we wanted to answer was are there any bats there at all?”

To find out, the team traveled to three sites along an elevation gradient, where two sensors were placed atop 12-foot poles for recording calls.

They were installed for six to seven nights per site for a total of 130 survey nights. The sensors recorded the patterns of the bats’ echolocation, their method of finding objects by reflected sounds.

“We were looking across essentially the full north-south gradient of the Absaroka Mountains east of Yellowstone National Park in the Shoshone National Forest,” Riggio said. “Our bottom most points are at 2,400 meters, that's a little less than 8,000 feet. Our highest point that we surveyed was 3,600 meters (about 12,000 feet) and so we had detectors spread out every 200 meters along a drainage of that elevation gradient.”

The team thought it had found one or two bat species at the various sites, so was surprised when they discovered five to seven species at the highest-elevation sites.

“It's a large species guild that's occupying these high alpine areas and using what are a pretty rich resource — insects in these alpine meadows that are available to bats,” Anco said.

What wasn’t clear was if the cold nights affect their ability to find forage. There’s also not a lot of great roosting habitat because there's no trees, so are the bats moving up and down in elevation every night to access those sites and then back down to roost during the day?

“We still don't know, that part is still a mystery,” Riggio said. “Where do these high elevation bats spend their days?”

  • Jason Riggio and Corey Anco do a vegetation survey at one of the high-elevation sites to help build an occupancy model.
    Jason Riggio and Corey Anco do a vegetation survey at one of the high-elevation sites to help build an occupancy model. (Draper Natural History Museum/Buffalo Bill Center of the West)
  • The group records data collected at one of its high elevation sites.
    The group records data collected at one of its high elevation sites. (Draper Natural History Museum/Buffalo Bill Center of the West)
  • Jason Riggio and Corey Anco deploy an acoustic sensor in the rain.
    Jason Riggio and Corey Anco deploy an acoustic sensor in the rain. (Draper Natural History Museum/Buffalo Bill Center of the West)
  • The research team that helped deploy acoustic sensors included (from left) volunteer Brian Beauvais, Co-Principal Investigator Corey Anco, volunteer Molly Quaranto, Co-Principal Investigator Jason Riggio, volunteer Paige Martinez and volunteer Bre Allison.
    The research team that helped deploy acoustic sensors included (from left) volunteer Brian Beauvais, Co-Principal Investigator Corey Anco, volunteer Molly Quaranto, Co-Principal Investigator Jason Riggio, volunteer Paige Martinez and volunteer Bre Allison. (Photo by Joshua Metten)
  • After retrieving equipment from one drainage, the research team including (from left) Co-Principal Investigators Jordan Harrison, Jason Riggio and Katy Goodwin immediately traveled to the next drainage and deployed the first of eight acoustic sensors.
    After retrieving equipment from one drainage, the research team including (from left) Co-Principal Investigators Jordan Harrison, Jason Riggio and Katy Goodwin immediately traveled to the next drainage and deployed the first of eight acoustic sensors. (Photo by Corey Anco)
  • A fully loaded overnight pack weighs between 45 and 60 lbs and includes layers, food, sensor equipment, and sleep systems.
    A fully loaded overnight pack weighs between 45 and 60 lbs and includes layers, food, sensor equipment, and sleep systems. (Photo by Joshua Metten)
  • An acoustic bat detector station is set up in the southern Gallatin Mountains.
    An acoustic bat detector station is set up in the southern Gallatin Mountains. (Draper Natural History Museum/Buffalo Bill Center of the West)
  • Volunteer Levi Cvikel (from left), Co-Principal Investigator Corey Anco and Co-Principal Investigator Jason Riggio hike to deploy sensors.
    Volunteer Levi Cvikel (from left), Co-Principal Investigator Corey Anco and Co-Principal Investigator Jason Riggio hike to deploy sensors. (Photo by Joshua Metten)
  • Some sites require long hikes into the backcountry. Too much to do in one day on foot. After deploying the first 3 sensors, the team set up camp above 3,100 meters or 10,000 feet before deploying the remaining three sensors.
    Some sites require long hikes into the backcountry. Too much to do in one day on foot. After deploying the first 3 sensors, the team set up camp above 3,100 meters or 10,000 feet before deploying the remaining three sensors. (Photo by Corey Anco)
  • Co-Principal Investigator Jason Riggio sets up a Pettersson D500X acoustic sensor near a creek on Carter Mountain.
    Co-Principal Investigator Jason Riggio sets up a Pettersson D500X acoustic sensor near a creek on Carter Mountain. (Photo by Corey Anco)

Second Year Split

In their second year of study last summer, the group split to expand its coverage. Anco and Riggio continued to work in Wyoming, increasing the size of the area surveyed.

As they had yet to answer at what point bats are no longer using the landscape, they pushed higher in elevation.

“So year two was to get more representation to see if the large amount of diversity in year one was an anomaly that we observed, or was it a pattern,” Riggio said.

To answer that question, they expanded to five additional sites to increase the sample size. That was no easy task going up steep landscapes with heavy equipment (each sensor weighs 20 pounds with fully loaded packs totaling up to 50 to 60 pounds and carried up to 10 to 16 miles per day).

“We really have the farthest north 10,000-plus-foot mountain in the Absarokas and within Wyoming, and the farthest south 10,000 foot mountain that's outside of wilderness,” Riggio said. “We've looked along the whole north-south component of where we're allowed to survey outside of wilderness in Wyoming in the National Forest.”

All the detectors except for the highest at 3,800 meters recorded bat activity last year. The top sensor was lost during sampling, so it is still unknown if there are bats there.

“We think a bear ran away with our equipment,” Riggio said. “We found most of the equipment, but it was spread over a large field and it was torn apart and they got about two nights of recording and then a recording of snuffling and metal being dragged across the landscape.

“So unfortunately, we can't say that bats aren't continuing up higher, but that was our only one at that elevation.”

Alpine Bats?

Meanwhile, Goodwin and Harrison, who are based in Bozeman, worked in Montana and deployed sensors in Custer Gallatin National Forest, specifically in the northern Absaroka Mountains and the northern Gallatin Mountains between Bozeman and Gardiner, Montana.

Their work was focused on seasonal patterns of bat activity in alpine habitats, which they defined as areas above tree line and at elevations of about 9,500 feet or higher.

“We set up acoustic bat detectors at four alpine sites in early July,” Harrison said. “Then, throughout the summer and fall we revisited the detectors every few weeks to check that they were still functioning properly, install fresh batteries and collect the SD cards containing acoustic data. We maintained the detectors in these same four locations until we retrieved the equipment in early November.”

The two wanted to investigate if bats are present in alpine habitats throughout this entire summer through fall time period, and are different species using alpine habitats at different times of year.

“In addition, we conducted short-term opportunistic acoustic sampling at four additional locations,” Goodwin said. “For these locations, we operated a handheld bat detector for anywhere from a few hours to overnight while we were camping.”

While they are still processing and analyzing the acoustic data from 2023, so far Goodwin and Harrison know that they recorded bats at every long-term and short-term site sampled in Montana last year.

“Within the first three weeks of sampling in July 2023, we collected hundreds of acoustic recordings of bats at all four seasonal monitoring sites, with multiple species at every site,” Harrison said. “We also recorded bats late into the fall, at least as late as the third week of October. We documented bat activity at multiple sites even after the first snow storms had occurred.”

A Pallid bat crawls on a rock.
A Pallid bat crawls on a rock. (Doug Keinath, National Park Service)

Expanding The Study

This summer in Wyoming, they plan to add two additional alpine sites for the final year of research, bringing the total to 10.

Two of the sites will be new while the third is a site they visited the first year, but they are now allowed to go slightly higher in elevation.

“So, we’ll have the full potential elevation gradient at each of those sites,” Riggio said.

In Montana, they first plan to revisit one of the long-term seasonal sites they monitored in 2023. They set up an acoustic bat detector there in early June to investigate if there is any bat activity prior to early July.

“We wanted to revisit this site because July was the earliest we were able to deploy our equipment last year, and we hypothesize that there may be bat activity occurring earlier in the season,” Goodwin said. “We will maintain this bat detector for a few months to add onto the long-term seasonal data we collected last year.”

Secondly, Goodwin and Harrison will be conducting short-term sampling at various alpine sites in the Beartooth, northern Absaroka and Madison mountain ranges, with the goal to document if bats are present at each site, and if so, what species are represented.

“Our short-term sampling will be accomplished by backpacking to high elevation areas and bringing a small handheld acoustic bat detector to collect recordings for 1-2 nights per site while we camp there,” Harrison said. “This method allows us to collect data without installing any equipment, which is critical when we are working in federally designated wilderness areas.”

All work between both groups, including in designated wilderness areas, is permitted through the U.S. Forest Service.

“We worked carefully with the permitting office and the head rangers to ensure that our survey methods were low impact, scientifically defensible, and in keeping with the spirit and law of wilderness protections,” Harrison said.

Bats roost in the rafters of a building at Devils Tower.
Bats roost in the rafters of a building at Devils Tower. (National Park Service)

Laying A Baseline

The samplings from 2024, in combination with the data collected in 2022-2023 in Montana and Wyoming, will help the group understand the geographic distribution of bats in alpine habitats across the whole Greater Yellowstone Ecosystem.

With that information, they plan to build occupancy models that will give the probability of the different bat species at any given habitat type and elevation range within the mountain system.

At each location surveyed they’ve also conducted a vegetation survey and determined site characteristics, such as where the closest water body is located and if there are heavy, dense trees. All the information will be input into the model.

“That way we can get a better sense of actual occupancy or habitat use,” Anco said. “Using the model, at some point we might be able to say from 2,800 to 3,000 meters, hoary bats are found, and they're found in association with this type of vegetation, vegetation characteristics or distance from water. That’s what the model is.”

From there the model can help determine where else the bats may be present based on those parameters.

“We can't tell you how many of this species are out there, but we can say this species is using this habitat,” Anco continued. “Bats are an indicator species. What that tells us is their presence or absence on the landscape is an indication of the relative health of that ecosystem.

“If they are found there and they are thriving, that means that the ecosystem is in relatively good health.”

The study can also be used as a baseline, so if the work is repeated in 10 to 20 years changes can be noted. The information could also lead to new studies, including discovering the exact diet of the bats and how they’re actually using the alpine habitats.

“We're seeing in our preliminary data that for some of these species 3,000 meters is their upper limit, which is about tree line here,” Riggio said. “So if the tree line pushes another 200 to 400 meters up in the next 20-30 years, do those bats respond and also begin to occupy that habitat as well? That'd be something fun for future researchers to look at.”

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Amber Steinmetz

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