The Marten - Lean, . . . But Mean Enough?

The American marten (Martes americana), another member of the weasel family, makes its western home in the old growth forests of the Rocky Mountains and Pacific Northwest. Few people ever see its fox-like face peering from its daytime resting sites in the crowns of trees or in cavities of hollow logs and trees. In the winter, this elusive hunter spends much of its time beneath the snow, accessing this "subnivean" world by way of natural tunnels under downed trees and branches, most abundant in undisturbed old growth.

The marten is so exquisitely tuned to its surroundings that it can depress its resting body temperature in the winter many degrees, therefore minimizing energy expenditures during the stressful winter months. Nonetheless, as one of the leanest animals known, with less than 4% body fat, the marten must eat nearly every day of the year to survive. During winter, beneath the deep snow on the forest floor, the heat of decaying material and the soil itself melts the bottom layer of snow, creating a cave-like space. Voles and other small mammals that martens eat spend most of the winter active in this space between the ground and the bottom layer of snow. The marten needs the large downed material from trees to gain access to this space, and to find places where it can rest without losing too much of its body heat.

Like its larger cousin, the fisher, the marten needs overhead cover. The marten has one of the narrowest ranges of habitat types of all of the forest carnivores. Marten are very rarely found above the timberline. They seem to require mature stands of mesic (moisture loving) conifers, particularly with lots of woody debris near the ground. Marten particularly avoid clearcuts, though they seem tolerant of some of the other kinds of disturbances that affect other forest carnivores.

Although the marten has suffered less than the other forest carnivores from changes to its habitat, the marten has been extirpated from many areas due to logging or trapping or both. Currently, the marten is found in patchy populations that reflect the forested "islands" that remain of its formerly widespread habitat throughout the Rocky Mountains and Pacific Northwest.