Over the past two years the National Park Service brought 19 wolves captured from a variety of places to Isle Royale National Park to restore the predators on an island overrun with moose.

Nearly half the wolves died shortly after being released. Some died of unknown causes, one died of pneumonia, but most were killed by other wolves in territory battles.

One group of the newly released wolves, however, has thrived on the island, and it's the group that was in the worst condition — on the brink of starvation — when it was released.

Seven of the eight wolves that were moved from Michipicoten Island in Ontario have started forming packs, securing territory and having pups, according to the latest annual report from researchers at Michigan Technological University in Houghton.

That's surprising to researchers and biologists because those wolves were so emaciated when released that they didn't even meet health conditions set by the Park Service. Exceptions were made for them as a sort of rescue mission because Michipicoten Island had run out of prey, said Rolf Peterson, research professor at Michigan Tech.

Yet nearly all survived, while seven of the 11 healthier wolves taken from Minnesota, Michigan and the Ontario mainland died.

It's not exactly clear why they've done so well. But it may be because once the starving Michipicoten Island wolves got some food in their stomachs they turned out to be, well, enormous.

"Their bodies are so huge, exceptionally large, as large as Yellowstone wolves," Peterson said.

The skull of the one Michipicoten wolf that died was an inch-and-a-half longer than average, making it and its pack mates some of the biggest wolves in North America, Peterson said.

That size goes a long way when survival depends on fighting off rivals and taking down animals as powerful as moose, he said.

Because of the Michipicoten pack's success, signs are promising that wolves will soon be fully re-established on Isle Royale despite the high overall death rate.

The remote Lake Superior island is in a new era. For decades, park managers were careful not to interfere with the natural booms and busts of wolf and moose populations there. Wolves had been naturally present since at least the 1950s, when a few crossed an ice bridge to get there. For almost a century the predator's numbers would rise when there were abundant moose and then crash after too many moose had been killed and eaten.

But by 2018, the island's wolf population had dwindled to a nine-year-old female and an 11-year-old male, ancient for a wild wolf. With almost no predators the moose population was rising by 20% a year, decimating trees and saplings where the animals foraged. The Park Service decided not to wait for new wolves to arrive on another ice bridge.

The last native female hasn't been seen in more than a year and is presumed dead. The male, likely the last native wolf on the island, was found dead in 2018. A necropsy completed this fall showed it had died after suffering internal injuries from fighting one of the released wolves. A younger wolf likely would have survived, Peterson said.

The old wolf was underweight and arthritic, he said, but aside from having an extra vertebrae, didn't have any spinal problems or other common abnormalities among inbred wolves.

It remains to be seen if the new wolves will intermingle enough to bring some genetic diversity to the island. The wolves seem to have split into four groups, researchers found. Two closely related wolves from Michipicoten seem to have joined up and taken over the eastern side of the island. The other three groups, made up of just a few wolves each, are a blend of mainland and Michipicoten wolves. In a promising sign, at least one of those genetically diverse groups likely had a pup, Peterson said.

The wolves are doing their jobs. This year marked the first time in nearly a decade that the moose population did not rise, remaining flat. As the wolves get more established and the pups start to grow, the moose numbers will certainly decline, Peterson said.

"So now we'll see if the vegetation responds," he said. "These trees just got hammered by the moose."

The numbers of predators and prey never quite balance out on Isle Royale. They're always in flux.

"There are established packs that are reproducing," Peterson said. "So now it's just wait and see for the predation effects, which I expect will follow shortly.

Greg Stanley • 612-673-4882