Wolves preying on beavers in Minnesota reshape wetlands

WASHINGTON (AP) — One spring afternoon in 2015, biologist Thomas Gable followed signals from a gray wolf’s GPS tracking collar to a small stream in Minnesota’s Voyageurs National Park. There he found a large canine paw print in the mud and tufts of wolf and beaver fur caught in low bramble.

A beaver had fallen victim to a wolf, Gable deduced. The industrious rodent's work in progress stood nearby — aspen logs, stripped clean, spanned the stream, and a pond about a foot deep was forming behind them. But when Gable checked again 10 days later, the dam had begun to collapse. With no aquatic engineer to repair the structure, the pond had disappeared.

“The water had totally vanished,” said Gable, who is based at the University of Minnesota. But the episode sparked an idea.

Over the next four years, biologists placed GPS collars on about 30 wolves inside the park. Then they visited every location where wolves had lingered for more than 20 minutes and searched the ground for clues about animals they preyed upon. They also documented when new beaver dams were abandoned nearby.

“Once a wolf takes out a beaver," Gable said, “it takes a while for another beaver to return to the site."

At each abandoned dam site studied, it took more than a year for another beaver to return, according to research published Friday in the journal Science Advances.

Wolves preying on beavers profoundly affect northern Minnesota's wetland ecosystems because dams built by individual beavers — those not associated with beaver colonies — quickly fall apart. The new research doesn't show wolves reduced the total beaver population in Voyageurs National Park, but that they influenced where beavers were able to build and maintain dams and ponds.

On average, there are about 73 wolves in...