UW Researchers Examine Columbia Spotted Frog Population in Big Horn Mountains

Anicka Kratina-Hathaway follows the frogs.

The University of Wyoming master’s degree student in zoology and physiology spent last summer studying the Columbia spotted frog in and near Sibley Lake, located in the Bighorn National Forest west of Sheridan. And she will be back this summer, tracking the amphibians via transmitters attached around the frogs’ bellies.

“Last summer, we got out over 40 transmitters (attached to the frogs) over any given time,” says Kratina-Hathaway, who created the miniature belts that hold the transmitters in place. “This field season, late May to mid-August, we hope to have 30-35.”

Kratina-Hathaway and her faculty adviser, Anna Chalfoun, are studying these particular frogs to better understand how this isolated Sibley Lake sub-population is connected to other Columbia spotted frogs in nearby ponds, lakes and wet meadows. The two-year research project is funded by the Wyoming Game and Fish Department.

Globally, amphibians are declining faster than many other species, including birds and mammals, says Kratina-Hathaway, who received her bachelor’s degree in organismal biology and ecology from the University of Montana-Missoula. She cites habitat change and loss, climate change and a fungal infection called chytrid as some of the reasons.

“Frogs are considered environmental indicators,” says Chalfoun, a UW assistant professor in the Department of Zoology and Physiology, and an assistant unit leader for wildlife with the Wyoming Cooperative Fish and Wildlife Research Unit. “Because of their permeable skin, limited mobility and reliance on both aquatic and terrestrial habitats, they can shed light on the current state of the system.”

Columbia spotted frogs in Wyoming are classified as a Species of Greatest Conservation Need (SGCN). An SGCN designation is intended to identify species whose conservation status warrants increased management attention and funding, as well as consideration in conservation, land use and development planning in Wyoming. An SGCN designation can be derived from known population or habitat threats, or, in the case of the Columbia spotted frog, there is a lack of sufficient information to adequately assess a species’ status.

There are no exact numbers known for the frog in the Big Horns, but the population has been described by the U.S. Forest Service “as viable at a minimum level,” says Zack Walker, the state herpetologist with the Wyoming Game and Fish Department.

Making connections

“We don’t really understand how well these Columbia spotted frog populations are connected,” Chalfoun says. “Preliminary surveys show there are a lot of frogs breeding at Sibley. How connected is this breeding spot to others? If something happens to Sibley Lake and that area, would the entire sub-population crash?”

“We are hoping to determine whether these frogs move and how they are related genetically,” Walker adds. “The Big Horn Columbia spotted frog population is genetically distinct from other populations due to its geographic isolation. Populations are dispersed and may not be connected.”

The Columbia spotted frog is medium-sized, reaching lengths of up to 3.5 inches. Its color ranges from a dark, olive green to a light brown, with irregularly shaped black spots on its back and legs. Its dorsal skin has a bumpy or wart-like texture. It has a long, narrow snout and upturned eyes. It is aquatic, with its feet webbing extending all the way to its longest toe. The frogs control invertebrate populations, primarily feeding on insects and arachnids.

While the Columbia spotted frog can lay hundreds of eggs at a time, very few hatch and make it to adulthood, Walker says. The concern stems from the fact that these frogs don’t travel great distances, as daily movement typically ranges from 1 to 10 meters.

“They utilize different habitats for different reasons,” Chalfoun says. “They’re not super mobile. They’re not a big elk or a bird that can fly away. It makes them vulnerable.”

For example, the frogs have to be wary of blue herons that hunt for fish in Sibley Lake and surrounding ponds. Ravens, weasels, mink and possibly fish are other predators of the adult frogs, Walker says. Robins, ducks, blackbirds, kingfishers, other smaller birds and some aquatic invertebrates have been known to eat the tadpoles.

And, as Kratina-Hathaway discovered, the frogs can even make a meal for a garter snake. Following the transmitter signals unique for each frog, she found, in two cases, the signal was emitting from the slithery reptiles.

“One transmitter failed and was lost within the garter snake,” she says. “Another we retrieved after the garter snake pushed it through its system.”

Interesting movement recorded

Last summer, transmitters were used at six different sites in and around Sibley Lake and nearby water bodies to record the frogs’ travel habits to breeding, foraging and wintering habitats. Kratina-Hathaway says she witnessed healthy frog populations at Sibley Lake, but that numbers were less at the other sites because breeding sites were smaller. However, part of her research is to look at frog movements to and from all of the identified breeding ponds.

“We’re interested in connectivity within and between the sub-populations. How much gene flow and genetic diversity is there?” she says. “I think our project is pretty cool because it’s one of the only studies that combine extensive telemetry with a lot of genetic samples to examine amphibian population connectivity, movements and habitat use.”

And while these frogs are not known to travel great distances (some transmitters only recorded distances of 100 meters over a couple of days), Kratina-Hathaway found one frog to be particularly adventurous.

“One frog moved over one-half mile,” she says. “This frog left its breeding pond, crossed a road, traveled through a wet meadow following a stream up-slope to eventually settle in a permanent pond where it will likely overwinter."

Another surprise is that a couple of frogs crossed heavily traveled dirt roads to reach a habitat while one traveled over a dam to reach Sibley Lake.

“These are things I thought would be barriers to movement, but they weren’t,” says Kratina-Hathaway, who has previous experience monitoring movements of birds, including eagles, ravens and songbirds.

This summer, night tracking surveys of the frogs will be conducted, something that was not done last year, she says.

When the research is complete, the goal is to submit papers to be published in peer-reviewed journals, such as the Journal of Wildlife Management or the Journal of Herpetology, Chalfoun says.

“With the information being gathered, we are hoping to learn how to restore meta-population connectivity, and learn about how related each population is within the Big Horns,” Walker says. “The ultimate goal is to ensure that this population remains healthy and viable in the Big Horns.”

Hear Anicka Kratina-Hathaway’s description of the Columbia spotted frog research in the Bighorn National Forest.