Primarily night hunters, they spend much of the day resting in trees or dens. They do most of their hunting on the ground, but are agile tree climbers. Marten stay active all winter. They hunt small mammals under the snow by using natural crevices around stumps or fallen trees. When the forest is clear-cut, the snow layers change and the natural avenues to their winter food sources are eliminated.
Females are almost three years old before they have their first litter.
Generally loners, they come together only briefly during the mid-summer breeding season, often mating with several partners. Birth occurs 220-276 days after fertilization. For most of that time, the egg is in a resting state, known as delayed implantation. The active pregnancy lasts only 27 days. The kits are born in March or April, weigh approximately one ounce and are blind, deaf and naked for the first two to three weeks.