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Invasive Bullfrogs Rapidly Colonize Yellowstone River
15 Oct
Summary
- Bullfrog spread increased from 37 to 66 miles along the Yellowstone River.
- Breeding sites surged from 12 to 45, indicating rapid population growth.
- Human activity is the primary cause of bullfrog introduction to Montana.
American bullfrogs have significantly expanded their territory in Montana's Yellowstone River floodplain. By 2013, their range covered approximately 66 miles, a substantial increase from 37 miles recorded in 2010. This period also saw a dramatic rise in breeding sites, from 12 to 45.
USGS researchers identified that human actions were the likely cause for the bullfrogs' presence near Billings. These frogs, native to eastern North America, were found in habitats like ponds and impoundments, which would have been difficult to reach naturally. Their ability to reproduce quickly and broad diet make them successful colonizers.
The species was first documented in the area in 1999. By 2010, 2012, and 2013, surveys confirmed bullfrogs were well-established and spreading both upstream and downstream. The invasion advanced further downstream, potentially aiding the dispersal of bullfrogs and their offspring into new areas.
Scientists have noted that bullfrogs can threaten native amphibians and reptiles due to competition and predation. In the Yellowstone River area, northern leopard frogs are of particular concern due to overlapping habitats. While no measured decline in local leopard frog populations had been confirmed by the time of the study, monitoring is essential.
A separate 2016 effort by the USGS investigated methods for bullfrog suppression, including trapping and removal. The agency acknowledged the difficulty in eradicating established bullfrog populations due to their prolific reproduction and mobility. The 2010-2013 data provides a baseline for the invasion's speed and highlights key habitats for future monitoring and prevention efforts.
