The western marten is arboreal. Its principal habitat in Washington is the Canadian Life-zone forests of the Olympic, Cascade and Blue mountains and the various ranges in the northeastern part of the state. At one time it ranged near sea level along the densely forested coastal belt and may still do so in the more rugged parts of the Willapa Hills. The marten is both diurnal and nocturnal. In Mount Rainier National Park the species has become quite tame and may be seen in the daytime. Many of the small mammals upon which it feeds are diurnal, but others are nocturnal. The marten is active throughout the year. Trappers report that during a storm the marten "holes up in rock slides" where it lives on conies and chipmunks until the storm passes. It spends a large part of its time in trees, and travels through them for long distances. It climbs more skillfully than the tree squirrels upon which it feeds. On the ground or on snow the marten travels in bounds, a yard at a leap, and its characteristic bounding gait forms tracks that are distinctive and easily followed. Mammals of the weasel family mostly are not gregarious but the marten is exceptional in that in the winter it travels in bands of 6 to 10 animals. Individuals composing these bands are inclined to wander but nevertheless the whole band travels in a definite general direction at a good rate of speed. Travel-ways or "runs" may be used by more than one band, and a run may extend for many miles, perhaps for as many as 50. A band of martens may take two weeks to complete the circuit, but usually returns to the starting point in less than a week. Most runs are about "half-way up the mountain," or midway between the crest of the hill or timber-line and the floor of the stream valley below. In summer the marten ranges higher; it lives in the trees just below timber-line and in the talus slides near timber-line. When the snows are unusually late the martens may keep to these higher areas until November. The food of the marten consists principally of small mammals and probably birds; the staple food in winter is the Douglas squirrel. In summer they feed on pikas, mantled ground squirrels and chipmunks. Mice, also, are eaten. The deer mouse, _Peromyscus maniculatus_, is usually abundant about old cabins and is successfully used as bait by trappers. Wood rats and flying squirrels are also eaten, the latter being especially important in certain areas. The tracks of martens that had been following snowshoe rabbits were seen on several occasions but the martens had turned off before a kill was made. In every instance the rabbit tracks indicated that the animals were hopping leisurely and browsing; apparently the tracks were made some time before the marten began to follow them.