The Wolves of Isle Royale

Wolves first arrived on Isle Royale in the middle of winter 70 years ago. They traveled from the mainland over an ice bridge that formed on Lake Superior. When spring arrived, the bridge melted, leaving the pack stuck on the island. Luckily, there were plenty of moose for the wolves to eat, and the pack thrived.

But over time, inbreeding decimated Isle Royale’s isolated wolf population. Members of the small pack mated with one another. Over generations, the wolves on the island became closely related. This increased the chances of offspring inheriting the same genes—units of hereditary material—including those for unhealthy traits, from both parents (see Passing On Genes). As a result, each new generation of wolves had more and more health problems. Crooked spines and extra vertebrae and ribs became common among the wolves. These abnormalities made it difficult for them to survive in an already harsh environment.

Wolves first came to Isle Royale 70 years ago. It was the middle of winter. An ice bridge formed on Lake Superior. The wolves traveled from the mainland over this bridge. When spring arrived, the bridge melted. The pack was stuck on the island. Luckily, the wolves found plenty of moose to eat, and the pack thrived.

But Isle Royale’s wolves were cut off from others. Over time, inbreeding destroyed their population. Members of the small pack mated with one another. Over generations, the wolves became closely related. The chances increased of offspring receiving the same genes—units of hereditary material—from both parents (see Passing On Genes). That included unhealthy genes. So each new generation of wolves had more and more health problems. Many had crooked spines and extra vertebrae and ribs. These problems made it even harder for them to survive in their harsh environment.

“This has been a long-term issue for the wolves on the island,” says Rolf Peterson, a wildlife biologist at Michigan Technological University. He and other scientists have been closely studying the island for more than 60 years as part of the longest-running study of predator-prey relationships. During that time, the researchers collected detailed data on how the island’s wolf and moose populations fluctuate (see Predators and Prey). It revealed a close connection between the survival of the two species.

“This has been a long-term issue for the wolves on the island,” says Rolf Peterson, a wildlife biologist at Michigan Technological University. He and other scientists have been closely studying the island for more than 60 years. Their work is part of the longest study of predators and their prey. During that time, the researchers collected detailed data on changes to the island’s wolf and moose populations (see Predators and Prey). It showed a close connection between the two species’ survival. 

Land animals can come and go from Isle Royale only in the coldest of winters, when ice bridges form. Decades ago, these icy pathways were available for about 50 days each winter. They allowed members of the Isle Royale pack to leave the island and wolves from the mainland to reach it. Once on Isle Royale, the new wolves would mate with the island pack, helping to increase its genetic diversity. Boosting the variety of genes within the population lessened the effects of inbreeding.

Land animals can come and go from Isle Royale only in the coldest winters. That’s when ice bridges form. Decades ago, these icy paths existed for about 50 days each winter. Members of the Isle Royale pack left the island over ice bridges. And wolves from the mainland came to Isle Royale. The new wolves would mate with the island pack. That helped to increase its genetic diversity. The population had a greater variety of genes and fewer effects from inbreeding. 

In the past 20 years, though, warmer winter temperatures have made ice bridges scarce. This has limited wolves’ ability to leave the island and chances for new ones to visit. “Fewer ice bridges stopped the trickle of new genes that arrived from time to time,” says John Vucetich, a wildlife biologist who now heads the decadeslong Isle Royale wolf study.

By 2018, only a male wolf and his daughter, both of them born of the same mother, remained on the island. Meanwhile, all around them, the moose’s numbers were increasing—along with their appetites. The moose ate saplings of various tree species, preventing them from growing into mature trees. In time, that would cause severe and potentially irreversible damage to the island’s forest. It would also disrupt the lives of other island species and set the moose up to starve. There was one obvious way to avert the disaster: Bring back the predators.

But in the past 20 years, winters have been warmer. Ice bridges are rare. It’s harder for wolves to leave the island or for new ones to visit. “Fewer ice bridges stopped the trickle of new genes that arrived from time to time,” says John Vucetich. He’s a wildlife biologist who now heads the decades-long Isle Royale wolf study.

By 2018, only a male wolf and his daughter remained on the island. Both of them had the same mother. At the same time, the moose’s numbers were increasing all around them, and so were the moose’s appetites. The moose ate young trees of different species. The young trees couldn’t grow into mature trees. In time, that would severely damage the island’s forest, and the damage could be permanent. It would also upset the lives of other island species. And over time, the moose would starve. One way to prevent the disaster seemed clear. Bring back the predators. 

As of September 2019, 17 wolves inhabited Isle Royale—the 15 introduced by the NPS plus the original father-daughter pair. Conservationists want the wolves to breed so their numbers will grow. The lack of variation in genes led to the original pack’s near extinction in the first place. Researchers know it’s important that new wolves brought to the island have a diverse genetic makeup. That’s why the scientists have taken pains to relocate animals from unrelated packs from the far-flung areas of Minnesota, Canada, and Upper Michigan.

By September 2019, 17 wolves lived on Isle Royale. They include the 15 brought in by the NPS and the remaining father and daughter. Conservationists want the wolves to breed so their numbers will grow. The lack of variety in genes almost wiped out the original pack. It’s important for the new wolves to have a diverse genetic makeup. That’s why the scientists have worked hard to find animals from unrelated packs. The new wolves are from far-off areas of Minnesota, Canada, and Upper Michigan.

Mark Romanski, the park’s chief of natural resources, says he’s blown away by the relocated wolves’ resilience. Just hours after undergoing capture and air travel to the island, they trot right off into the forest on the trail of their future pack mates, he says. These wolves, “will almost certainly know what to do when they encounter a moose.”

Mark Romanski is the park’s chief of natural resources. He says he’s blown away by how quickly the new wolves adapt. They’re captured and flown to the island. Just hours later, they jog right off into the forest to find their future pack mates, he says. These wolves “will almost certainly know what to do when they encounter a moose.”

Even with more wolves on Isle Royale, it’s going to take time to slow the momentum of the island’s flourishing moose population. “You’ve got to keep in mind that there are now 17 wolves versus 2,000 moose, plus all the uncounted calves born this past summer,” says Sarah Hoy, a wildlife ecologist who studies the wolves with Peterson and Vucetich.

When Vucetich and a team of biologists went to Isle Royale to do research in the late spring of 2019, they were amazed by the huge number of moose they encountered. And they were alarmed about the damage the moose were doing to the forest, in particular to balsam fir trees. “It’s now hard to find any balsam fir in a forest where it used to be abundant,” says Vucetich.

Now more wolves are on Isle Royale, but it will still take time to slow the growth of the island’s moose population. “You’ve got to keep in mind that there are now 17 wolves versus 2,000 moose, plus all the uncounted calves born this past summer,” says Sarah Hoy. She’s a wildlife ecologist who studies the wolves with Peterson and Vucetich.

Vucetich and a team of biologists went to Isle Royale for research in the late spring of 2019. They were amazed by the huge number of moose they found. And they were alarmed about the damage they saw. The moose were consuming the forest, especially balsam fir trees. “It’s now hard to find any balsam fir in a forest where it used to be abundant,” says Vucetich. 

Predators that rely on stealth, like wolves, are harder to glimpse than plentiful, lumbering moose. But scientists can learn what the elusive animals are up to by looking for their pawprints and scat, or droppings. “All the new wolves are also wearing GPS collars so that the National Park Service and researchers can track their movements and see if they’re alive,” says Hoy. The collars also help scientists determine if the wolves are joining the pack and choosing mates.

The team didn’t see any wolves during their trip early in 2019. But for the first time in years, they heard howling in the distance at night. It’s a sound that bodes well for a healthier Isle Royale.

Predators like wolves rely on surprise. They’re harder to spot than the many, slow-moving moose. But scientists can still learn what the mysterious animals are doing. They look for the wolves’ pawprints and scat, or droppings. “All the new wolves are also wearing GPS collars so that the National Park Service and researchers can track their movements and see if they’re alive,” says Hoy. Are the wolves joining the pack and choosing mates? The collars also help scientists figure that out.

The team didn’t see any wolves during their trip early in 2019. But they heard something for the first time in years. Wolves howled in the distance at night. The sound is a good sign for a healthier Isle Royale.