Invading bullfrogs will eat almost anything!
An invasion of American bullfrogs that will eat just about anything, including each other, is spreading downstream along Montana's Yellowstone River and poses a potential threat to native frogs, government scientists say.
Bullfrogs were found in surveys along a 66-mile stretch of the river from the Laurel area downstream to Custer, according to U.S. Geological Survey biologist Adam Sepulveda. The number of breeding sites for the frogs almost quadrupled between 2010 and last year, rising to 45 total.
"They are going to eat anything they can fit into their mouths. It doesn't matter if it's another frog or a bird or a mosquito," said Sepulveda, who co-authored a study on Yellowstone River bullfrogs appearing in the journal Aquatic Invasions.
Bullfrogs as long as 12 inches when outstretched have been found. One that was caught near the Audubon Conservation Center in Billings last year had a bird in its stomach.
State and federal agencies initially tried to stop the invaders in their tracks by killing them all off, but gave up after the number of bullfrogs overwhelmed the effort. They're now trying to come up with a strategy to at least contain their spread.
Bullfrogs are native to the eastern U.S., but are known to have been spread by humans to every state except North Dakota.
They've caused problems elsewhere by preying on native frogs, out-competing other animals for food, and spreading a fungus that's suspected as a cause of a widespread decline in amphibians, Sepulveda said.
They were first documented in eastern Montana in 1999. Scientists believe they descended from released pet frogs or bullfrog tadpoles used as bait by fishers.
The frogs have inhabited areas of western Montana since the 1920s, likely from a farming operation that sold their legs to be eaten, Sepulveda said.
Critical thinking challenge: Why do invading bullfrogs pose a threat to native frogs?