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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

American marten, also called pine marten, were never plentiful here, but active management is helping restore populations of these small mammals more quickly. © Erwin and Peggy Bauer, U.S. Fish and Wildlife Service

October 2008

A weasel with a secret

Discovering why marten are slow to recover in the Northwoods remains a work in progress and a bit of a mystery.

James C. Bishop, Jr.


American marten, also called pine marten, were never plentiful here, but active management is helping restore populations of these small mammals more quickly.

© Erwin and Peggy Bauer, U.S. Fish and Wildlife Service

In late September, at a remote site on the west side of the Chequamegon-Nicolet National Forest, 30 small weasel-like animals were quietly freed in a wooded area. Their capture and subsequent release are part of a continuing effort to revitalize wild populations of the American or pine marten, the only mammal remaining on the state's endangered species list.

Marten are members of the Mustelid family, carnivorous weasels that range in size from the tiny least weasel, to ermine, mink, skunks and otters on up to fishers and wolverines. The reddish-dark brown American marten (Martes americana) weigh between 1 to 2 pounds, and males grow up to 25 inches in length. Marten have plush, lustrous fur and long bushy tails that are one-third of their total length.

Most people visiting the forests rarely see marten because they shy away from any human activity and are almost exclusively active at night. In the Midwest, these solitary animals live in mature, dense conifer and hardwood woodlands making the northern national forestlands an ideal home.

Until 1925, American marten were widely distributed throughout northern Wisconsin but unregulated fur harvest and habitat loss eliminated the animals. Like other formerly displaced animals, including fishers, turkey and elk, reclaiming their niche in the natural landscape is part of our aim to restore natural diversity.

The Department of Natural Resources in cooperation with the U.S. Forest Service and other agencies, developed a marten recovery plan in 1986. The Great Lakes Indian Fish and Wildlife Commission (GLIFWC) later joined the group of active wildlife managers and researchers. The plan aims to reestablish a self-sustaining population of marten in the Chequamegon-Nicolet National Forest.

Over a period of 15 years, 300 marten were released in the forest with limited success. A mark and recapture study done by DNR Wildlife Biologist Jim Woodford estimated that marten populations in the northeast part of the release range of the Nicolet side have grown to about 220 animals.

"It appears these animals are holding their own." Woodford explained, "We have not noticed any increases or decreases in their numbers."

While the Nicolet marten have been surviving, the Chequamegon population in northwestern Wisconsin appears to be much lower as measured by winter track surveys and hair sampling, Woodford said.

Biologists from the three main agencies are trying to determine why marten populations are struggling. One theory considered is that an insufficient number of animals might have been released over such a wide area. The forest covers 1.5 million acres of land across the north.

There was also a concern with the sex ratio of the animals that were relocated and stocked. Woodford said more males than females were released during the reintroduction effort. Still, given that marten in similar ratios were released in both forests, it is uncertain why the Nicolet populations responded better than those in the Chequamegon region.

DNR Wildlife Technician Carol Eloranta takes samples from an anesthetized marten near Hiles, Wis.

© Jim Woodford
DNR Wildlife Technician Carol Eloranta takes samples from an anesthetized marten near Hiles, Wis. © Jim Woodford

Another factor may be predation. Fishers that are somewhat larger compete for similar foods and habitat as marten. Like their competitors, marten feed on squirrels, mice, shrews, rabbits, amphibians and reptiles. Bobcats and foxes that are plentiful in these forests also prey on similar foods.

When searching for food, marten sprint in a zigzag pattern across the forest floor stopping frequently to check for prey and predators. When threatened, they take to the trees. In a foot race scrambling through trees they can elude bigger animals.

A third reason these high energy animals may not be surviving well could be climate change. It appears, say biologists, that the animals need deep snows to gain a competitive edge on bobcats, foxes and fishers also hunting prey on the forest floor.

"The marten do better during years of high snowfalls in the north where they tunnel under snow in search of mice and other rodents," said Woodford. "When there is less snowfall, as we have seen in the last few years, they are at a disadvantage."

Marten are better adapted to deep snows as they are smaller, lighter and have hairs around the pads of their feet. The larger fisher cousin is not so well equipped.

Elimination of dry land trapping in and around areas where marten have been released has been a two-edged sword. On one hand, it has eliminated the incidental take of marten; on the other, it may have allowed increases in the numbers of fishers that prey on their smaller cousins.

Biologists continue to look for ways to improve marten populations. One proposal approved by the sporting public at last spring's conservation hearings would allow dry land trapping in areas where marten are released using cage or box traps and cable restraints. These traps are effective in taking fishers, foxes, coyotes and bobcats without harming marten.

A GLIFWC biologist, Jonathan Gilbert, has been studying marten in the forest since 1991. Gilbert has trapped, radio collared, and tracked them using telemetry equipment. He also measures the size and weight of each animal, and checks for parasites and evidence of reproductive success.

Gilbert also notes that marten, known as waabizheshi to the Ojibwe or Chippewa tribe of Native Americans, had historical cultural status as clan animals.

Over the next few years, 60 more marten will be released. Continued research, telemetry studies and winter tracking may provide clues for biologists to what management techniques can successfully return populations of this reclusive woodland resident to Wisconsin forests.

James C. Bishop, Jr. is public affairs manager for DNR's Northern Region and is stationed in Spooner.