Wyoming Wildlife - July 2019

Bullfrogs pose risk to native amphibians

One of these voracious frogs has been confirmed near Sheridan, and more have been reported in other parts of the state. Anyone who sees or hears a bullfrog in Wyoming is asked to report it.

7/1/2019 5:19:34 PM

SHERIDAN — While walking his dogs at Kleenburn Ponds north of Sheridan last summer, Bob Krumm heard a sound from his past, but he knew it didn’t belong in Wyoming. The Sheridan resident immediately recognized the distinct sound of a bullfrog as it began its nightly serenade, a sound he frequently heard while growing up in Michigan.
“I heard the bullfrog; I never did see it,” he said. “But there is no mistaking a bullfrog. I don’t know of any other sound that is like it. Like a loon or a sandhill crane, once you hear it, you can’t miss it. It is very distinctive.”
Krumm reported what he heard to the Wyoming Game and Fish Department Sheridan Regional Office. The next day Paul Mavrakis, Sheridan fisheries supervisor, and Andrew Nikirk, one of Sheridan’s two fisheries biologists, traveled to the ponds and found Krumm was spot-on when identifying the sound. They found the frog, but they were unable to catch it. Two nights later, Nikirk returned to the ponds and captured the bullfrog, maneuvering close to it with a rowboat. 
Bullfrogs are native to the eastern United States. When they are intentionally or accidentally introduced into new areas, they can have devastating impacts on native amphibians.
“It is unclear if bullfrogs were ever native to Wyoming,” said Game and Fish Herpetological Coordinator Wendy Estes-Zumpf. “Because they have been introduced to so many parts of the U.S. and other parts of the world, it is hard to know. But if they are native to any part of Wyoming, it is just a small area on the Nebraska border along the North Platte River drainage.  But they are not native to and should not be anywhere else in Wyoming.”
Aside from the confirmed bullfrog in Sheridan, other reports suggest they may be at Keyhole Reservoir, ponds in the Cheyenne area and Kelly Warm Springs by Jackson. Estes-Zumpf said the widely separated reports suggest the frogs might be accidentally or intentionally released pets or classroom projects.
Preventing bullfrogs from taking up permanent residence in Wyoming is critical. Their large size, aggressive nature and voracious appetites position them to out compete native amphibians. When they arrive in a new area, they can nosh their way through the inhabitants. Insects, small rodents, fish, birds, reptiles and even other amphibians are all potential menu items.
“They are extremely successful and prolific amphibians,” said Andrew Gygli, a herpetologist with Game and Fish who is conducting targeted bullfrog surveys in northeast Wyoming this summer. “Where they evolved in their native range, they have predators adapted to help control them and keep their numbers in check. We lack that predator base in our wetlands to really handle bullfrogs.”
An example of the devastating effect nonnative bullfrogs can have in an area can be seen just south of Wyoming.
“When you go to some of the ponds along the Front Range in Colorado, they are packed with bullfrogs and nonnative amphibians,” said Estes-Zumpf. “Leopard frogs in the Front Range are really declining and part of it is the severity of the bullfrog invasion. That is not uncommon. In areas where bullfrogs are introduced and did not previously occur, they either eat or out compete all the other amphibians. Once they get a good foothold, they are very hard to control.”
They also threaten native amphibians in another substantial way. In recent years, the fungal disease chytridiomycosis has decimated amphibian populations around the globe. The fungus destroys an amphibian’s natural ability to transfer gasses and water through the skin, which can result in the animal drowning or having a heart attack. Initial research suggests bullfrogs are less susceptible to the disease, allowing them to spread it while avoiding the disease’s lethal impacts.
In addition to Gygli’s survey effort, Game and Fish is asking the public to help identify potential new areas of bullfrog expansion by reporting suspected calls or sightings. Bullfrogs breed later in the season than the state’s native amphibians and are likely to be heard in July and August.
A short video featuring photos and recordings of bullfrog calls can be found above and at www.youtube.com/wygameandfish.
If you hear or see a bullfrog in Wyoming, email Andrew.Gygli@wyo.gov and include any photos of live or dead bullfrogs, video or audio recordings and a detailed description of the location.
      — Christina Schmidt is the Game and Fish public information specialist in the Sheridan region. She is a regular contributor to Wyoming Wildlife.


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