Isle Royale wolves increase while moose decline

After a year of translocation efforts in Isle Royale National Park, the island’s wolf population is flourishing again, with numbers around their historical levels.

Between October 2018 and September 2019, the National Park Service brought in a total of 19 wolves to the park in northwestern Michigan, where the wolves (Canis lupus) were considered important to keep the island’s moose (Alces alces) population in check.

A bull moose fitted with a GPS collar near Beaver Island at the west end of Isle Royale in February 2022. The bull ended up dying that spring of malnutrition. Credit: Sarah Hoy

Isle Royale has occasionally connected to the mainland during the winter, when an ice bridge allowed wolves to cross over from the north. But warmer temperatures haven’t allowed that bridge to form in the last few decades, and the wolf population plunged.

“Five years ago, there were only two wolves left on the island, and they were so inbred, they weren’t able to successfully reproduce,” said Sarah Hoy, the co-leader of the wolf-moose project and a research assistant professor at Michigan Technological University.

But the population is looking up. In a recent annual report, scientists reported an estimated 28 wolves.

“This last year has been really amazing,” Hoy said. “The population really increased in number, and we’re seeing signs of wolves doing everything we hoped they would.”

A large group of wolves were seen feeding on a moose on the ice near Daisy Farm at the east end of Isle Royale. Credit: Ky and Lisa Koitzsch

During aerial surveys, Hoy and her colleagues saw wolves traveling and resting together, and they spotted the tracks of others appearing to do the same, suggesting that the wolves were forming packs and reproducing. They also took note of them producing pups. “Wolves have the potential to reproduce and grow in number quite quickly,” she said.

“All of those things happening at the same time means that it’s been a tough year for moose and that’s probably why we’ve seen a significant decline in the number of moose on the island over the past two years,” Hoy said.

Hoy said she’s glad to see a healthy wolf population return to the island. “It’s certainly nice hearing from park visitors that heard wolves howling or saw wolf tracks,” Hoy said.