Photograph by John A. Vucetich

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A female radio-collared wolf crosses an ice bridge in February.

Photograph by John A. Vucetich

How Do Wolves Get to a Remote Island? Ice Solves Mystery

Female's trek nails down how wolves get to the Lake Superior island home of a controversial, and dwindling, wolf pack.

For the first time, a wolf has been tracked crossing an ice bridge into northern Michigan's Isle Royale National Park—an impressive feat that might be a hopeful sign for the predator's ability to survive climate change.

On February 22, the GPS-collared wolf left her territory in eastern Minnesota's Chippewa Grand Portage Reservation and trotted 14 miles (23 kilometers)—the shortest possible distance to her destination—across the rugged Lake Superior ice to Isle Royale, a remote, forested island that's home to an unrelated wolf pack. 

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An uncollared companion of unknown gender went with the female; the pair stayed on the island a few days before returning home.

An uncollared companion of unknown gender came with her; the pair stayed on the island a few days before returning home on February 27, according to GPS data collected by Seth Moore, director of biology and environment for the Grand Portage Band of Chippewa.

"It's cool on a bunch of different levels. First of all, it establishes conclusively how wolves get to Isle Royale—this was all speculation up until last week," says Moore.

Scientists have long predicted that wolves get to the island via ice bridges in Lake Superior. Since these bridges don't form reliably anymore thanks to rising temperatures in the region, some believe the future of Isle Royale wolves is tenuous at best.

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At the same time, the island wolf population has been steadily declining, according to scientists with the Wolves and Moose of Isle Royale Project. In 2009, scientists documented about 24 wolves living on the island. By February 2014, that population had dwindled to nine, says Rolf Peterson, a wildlife ecologist at Michigan Technological University in Houghton who has led the project since the 1970s.

The likely reason for the decline is inbreeding. With few outside wolves breeding with the island population, and therefore little genetic diversity among the remaining wolves, all the animals have skeletal deformities, and their weakened state could be interfering with reproduction.

Island Getaway

But Grand Portage wolves—whose range also includes parts of southern Ontario—are faring well. The wolf that was tracked to Isle Royale, dubbed Wolf 13264, has been documented several times traveling more than 50 miles (80 kilometers) from home, Moore says.

Wolves are constantly looking for new territories and mates, and can travel long distances, Peterson explains. "As soon as there's ice anywhere, they're on it," he says. "They like to move." 

As for what she and her buddy got up to during their jaunt on Isle Royale, there's little to go on—her GPS data is collected only once every 12 hours.

The duo did come within a few miles of the resident wolves, and it's even possible they interacted somehow—perhaps by howling, says Peterson, who has received funding from the National Geographic Society.

Maybe the collared female even evaluated the genetic fitness of the resident wolves by smell and decided not to join the pack, he speculated.

Next, scientists can watch the pair to see if they return to the island, which might mean they're scouting out new territory, says L. David Mech of the U.S. Geological Survey, who has also studied Isle Royale wolves. 

More Adaptable Than Thought?

Overall, the event "certainly calls into question a lot of the assumptions everyone has had," Mech says.

Seeing that wolves can so quickly and successfully travel over an ice bridge suggests the species may be more adaptable to climate change than thought, Mech says.

But will there be ice for the wolves to use? Mech notes that ice bridges have appeared in Lake Superior over the past two years, despite predictions to the contrary.

But Grand Portage's Moore says those bridges haven't lasted as long as in previous years—the one the wolf pair crossed in February is already gone.

The wolves' trek may also help the National Park Service decide whether to intervene to save Isle Royale's wolves, Mech adds. Some experts believe that unless new wolves are brought to the island, the pack there will die out. 

"If wolves can get over there more easily than we've assumed, with a temporary ice bridge that could form any winter," Mech says, "this would change that outlook."