The sound of the great plains toad is unmistakable to the trained ear. It’s jarring and repetitive like a jackhammer, said Asila Bergman, a wildlife acoustic specialist with Wyoming Game and Fish Department. The sound of several toads calling is disorienting and intense. When Bergman is trying to record the amphibians she puts in ear plugs because it can get so loud.
Still, she was thrilled when she and James Erdmann, a herpetology technician with Wyoming Game and Fish, heard the call earlier this summer in the Powder River Basin. Herpetologists study amphibians and reptiles.
They sat in a car with the window rolled down, capturing the sound on a hand-held recorder for more than half an hour, Bergmann said. They knew by the sound of so many calls they’d found a breeding population of the elusive toad.
It’s not that the toad is rare, but it’s hard to find because it breeds in flooded meadows and temporary ponds. It, like so many Wyoming amphibians, is hard to see.
It was one of the species Bergman wasn’t sure they’d be able to record this year.
Bergman and Erdmann are collecting audio recordings from toads and frogs in Wyoming for a project spearheaded by the Bureau of Land Management. The agency contracted the Game and Fish staffers to collect the audio to help identify what amphibians are living and breeding on BLM land across the state.
The baseline data can be used to see if the frogs and toads abandon areas or move to a new range, Bergman said. Each species has a distinctive sound, although some sounds are hard for people to differentiate between. Bergman also will use the collected acoustic data to create a computer-generated recognizer that can scan thousands of hours of audio and identify the vocals of specific species.
The technology has been used to monitor bats and it saves manpower and time once the initial audio data is collected and built into the program, she said.
It’s often easier to hear an amphibian than spot it, Erdmann said.
“If they are in the area during the breeding season, they are going to be calling,” he said.
Some of those calls can be heard more than a mile away, he said. Trying to find a frog or toad by sight is more challenging. The animals are small and well-camouflaged. A frog might call inches from your face and you still can’t see it, he said. Most toads are also most vocal at night, making it even harder to spot them.
On one survey in the Red Desert this summer, Erdmann heard a dozen toads calling from water-filled holes near a pond. He tried to triangulate the sound to see one, but every time he thought he approached where the call originated, it went silent. Despite scanning the area with his headlamp he couldn’t see a single toad.
At this point acoustics can only tell if a specific amphibian is in the area, Bergman said. That is still valuable information, especially for species of concern, like the Wyoming toad. Once they’ve been identified in a certain area, managers can check if they stay in the same place or change locations, she said. Monitoring the locations of species in decline, like the boreal toad, can help managers understand what is happening to the population, Bergman said.
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Sometimes acoustics give a sense of the species’ abundance in an area. But it’s difficult to do with amphibians because many croak at the same time, making it hard to pick out individual calls for a population estimate, Bergman said.
To collect audio, researchers need a sense of where the amphibians live. Bergman and Erdmann used data from the Wyoming Biodiversity Institute’s Rocky Mountain Amphibian Project to figure out where to record some species like the northern leopard frog. It has a quiet call and doesn’t chorus.
They found and recorded the frogs on Pole Mountain in Vedauwoo thanks to the project’s data. Even with information on previous sightings, the frog is so hard to spot that Bergman and Erdmann first searched for egg masses to make sure they placed their recorders near enough to breeding males to pick up the calls.
They recorded sounds with handheld recorders but also microphones they left in some breeding areas. They worked on BLM land across the state and, with permission, on some private land.
In Cheyenne they recorded a bullfrog population. In the mountains they recorded high-elevation amphibians like the boreal toad.
The two researchers had six species they wanted to record this summer to add to other frog and toad audio captured earlier.
Eventually they’d like to create a digital audio archive that other agencies and researchers can use.
Bergman also wants, depending on funding, to use the collected data to create protocols for scientists and managers in all agencies for identifying amphibian acoustics in Wyoming.