American bullfrogs spread along roughly 66 miles of Montana’s Yellowstone River floodplain by 2013, up from about 37 miles in 2010, according to a US Geological Survey report published in October 2014. Researchers also recorded an increase in breeding sites, from 12 to 45 over the same period, and the findings documented a rapidly expanding population of a frog native to eastern North America but introduced to the Yellowstone River region, near Billings, through human activity.
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