Bullfrogs are living up to their name by bullying across Montana’s flood plains and up the Yellowstone River, according to the United States Geological Survey. While this invasion may not sound serious, it could harm the ecosystem and be very difficult to contain.

A majority of America’s amphibian species have declined in recent years due to drought conditions and warmer temperatures. But the American bullfrog appears to be not only thriving, but spreading.

The American bullfrog is known for its adaptability, fecundity, and ability to eat almost anything. A female bullfrog can deliver 40,000 eggs per clutch, making the species difficult to contain due to their rapid reproduction rates. The bullfrog has also demonstrated advanced adaptability to different environments.

“The impacts of bullfrogs on native amphibians in the Yellowstone River are not yet known, but native Northern leopard frogs are likely to be most vulnerable to bullfrog invasion and spread because their habitats overlap,” said USGS scientist and lead author Adam Sepulveda. 

Sepulveda’s study collected field survey material from 2010-2013 along the Yellowstone River. The first American bullfrog was noticed in the area in 1999, but there now appears to be a large population that could spread to other areas and pose a threat to biodiversity.

The study, published in the journal Aquatic Invasions, detailed the bullfrog’s rapid expansion during the past few years. Bullfrogs covered a territory of 37 miles in 2010, but grew to inhabit an area of 66 miles by 2013. The number of breeding sites also increased dramatically from 12 sites in 2010 to 45 sites in 2013. Population expansion occurred both upstream and downstream, demonstrating the bullfrog’s ability to increase population growth in different areas through adaptability.

USGS scientists are attempting to stop the invasion, but have adopted a policy of containment. They will attempt to contain the amphibians to their existing area while preventing further population expansion.