The American bullfrog has expanded its invasion of the Yellowstone River floodplain in Montana, according to a new study released in “Aquatic Invasions.”

The study is the first of its kind to describe the rapid extent of bullfrog spread, as well as their preferred habitat along the Yellowstone River near Billings, Montana. Scientists with the U.S. Geological Survey’s Northern Rocky Mountain Science Center, Montana Natural Heritage Program, Bureau of Land Management, and Montana Fish Wildlife and Parks concluded that this invasive species is now thriving and rapidly spreading in the Yellowstone River.

Bullfrogs are thought to be a cause in the declines of multiple amphibian and reptile species around the globe. Bullfrogs are native to eastern North America, but are a relatively new invader in the Yellowstone River floodplain and were first documented in 1999.

To get an understanding of the extent of the bullfrog invasion, scientists conducted field surveys in 2010, 2012, and 2013. Results of the surveys indicate that bullfrogs are firmly established in the Yellowstone River floodplain and can rapidly spread to new habitats.

According to a news release, the findings give land managers a better idea of the extent of the bullfrog invasion so they can focus on prevention, early detection, direct removal, and restoration.