Males are the larger sex and weigh about 1000 g, whereas females weigh about 650 g. In winter, the soles of a marten's feet are covered with fur and the toes are not distinguishable in the tracks. Tracks are about 3.7 cm long and form two ovals that overlap by about one third. This happens because marten travel with a loping sort of gait, and the hind feet land in the tracks left by the front feet. Loping is common among mustelids, and it takes some practice to be able to distinguish the tracks of the various species.
Marten are solitary animals.
Even so, males and females spend time together only during the mating season in late July and early August. The female rears the young alone. Litter size is reported to range from two to six but is most often three, and the young are born in March or April, eight or nine months after mating. This is an abnormally long gestation period for a small mammal and results from a phenomenon known as delayed implantation. After mating and fertilization, development of the embryo stops at a very early stage.