Martens recolonized Isle Royale in the '90s, showing island's dynamism

August 24, 2018, University of Wisconsin-Madison

After decades of trapping, the last known American marten was spotted on Isle Royale in 1917. Fifty years later, in 1966, the National Park Service planned to reintroduce martens to the national park situated in Lake Superior, but nobody knows if the agency ever followed through. Then, in 1993, martens were confirmed on the island for the first time in 76 years.

Whether these small, forest-dwelling carnivores—valued historically for their fur—had been hiding there the whole time, found their way back, or were introduced in the 1960s without any records has remained a mystery for the last quarter century.

But in new research published today (Aug. 23, 2018) in the journal Scientific Reports, University of Wisconsin-Madison researchers in the Department of Forest and Wildlife Ecology, collaborating with the National Park Service, traced the recolonization to martens likely arriving in the 1990s, shortly before they were spotted.

Genetic studies of martens from Isle Royale and nearby populations in America and Canada showed that the contemporary population came from nearby Ontario, Canada. The animals likely wandered over on an ice bridge in the winter, the researchers speculate.

The results provide much-needed context about the natural history of an island long considered an unspoiled wilderness, but one with a long history of ecological disruptions and recoveries. The island park may be best known for the ebb and flow of its wolf and moose populations, which have been tracked for 60 years.

With additional wolves set to be relocated to Isle Royale in the coming months, the new research provides ecologists and land managers with a fuller picture of how dynamic even seemingly isolated island ecosystems can be.

After all, say the researchers, if the house-cat-sized marten can find its way over, islands like Isle Royale may be less isolated and static than we think.

Jonathan Pauli, a professor of forest and wildlife ecology at UW-Madison, has studied martens for years as part of efforts to understand how communities of wild animals respond to human disturbance. In 2015, his group provided evidence that martens had long escaped detection on islands in southeastern Alaska prior to deliberate reintroduction efforts in the 20th century. And in work published in 2016 with graduate student Phil Manlick, Pauli called into question the effectiveness of periodic augmentations of reintroduced marten populations in Wisconsin, where the once-extirpated carnivore remains an endangered species.

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