Martens returned to the Apostle Islands on their own, genetic work shows

The American martens now living on Wisconsin's Apostle Islands were not brought there. Genetic research indicates the population spread to the islands naturally from a closely related population in upper Michigan, and does not descend from the Pacific martens released in the 1950s. This National Park Service article, written by Kassandra Arts for Apostle Islands National Lakeshore, tells how the animals were lost and found again.

American marten. NPS photo/M. Van Valkenburg

A small, rare weasel

American martens are small, rare weasels of mature forest in the upper Midwest. They are state endangered, living only in small populations at the northern edge of their former range. People often confuse them with fishers, but martens are smaller and have proportionally larger ears.

Lost, released, lost again

Martens were thought to have been wiped out locally in the 1930s, after intense logging and development degraded and destroyed their habitat. In the 1950s ten Pacific martens from Montana and British Columbia were released on the islands. That effort failed, and the last marten was detected there in 1969. On the mainland, further releases in the nearby Chequamegon-Nicolet National Forest between 1970 and 2010 had some success, creating a network of marten populations across northern Wisconsin and Michigan's Upper Peninsula, using animals brought from Ontario.

Found again

Remote camera image of an American marten on a dead birch tree. NPS photo

In 2014 a marten was seen on Manitou Island, which led to the discovery of a photograph of an island marten from 2010. Projects with the University of Wisconsin-Madison and Northland College began, aiming to find which islands had martens and where they came from. They used scat and hair collected for DNA, and remote cameras. As of fall 2021, martens had been located on Bear, Cat, Oak, Ironwood, Manitou, Otter, Outer, Rocky, Sand and Stockton Islands, with the first marten seen on Oak and Ironwood in 2021. Hair and scat sampling in 2017 indicated these numbers:

Remote camera image of a marten in snow. NPS photo

The genetic work found that the martens in the park arrived by natural dispersal, a recolonization thought to be fairly recent, roughly 20 years before the article. Forty-three island martens were identified, and most live close to immediate family. Some have moved to other islands or the mainland, which suggests the denser island populations may serve as a source for the mainland, where they could bring some genetic diversity to thinner, declining populations. The article says the higher density in the park is hypothesized to be linked to more complex forest, more prey and less competition with other predators.

Remote camera image of an American marten approaching the camera. NPS photo

What next

The article concludes that the islands can serve as a refuge for martens, with preferable habitat as the climate changes, and that the national lakeshore protects them from development and other disturbance. Continued research will be needed to track the new population, because limited gene flow from the mainland could hurt a small island population over time.

Sources

• National Park Service, Apostle Islands National Lakeshore, "American Marten on the Apostle Islands", written by Kassandra Arts (https://www.nps.gov/articles/000/american-marten-on-the-apostle-islands.htm); rewritten in hubnx's own words.