They may be either diurnal or nocturnal but are generally more active at night. Some species engage in the year-round activity of sliding down mud and snow banks, and individuals of all ages participate. Sometimes they tunnel under snow to emerge some distance beyond. The diet consists largely of fish, frogs, crayfish, crabs, and other aquatic invertebrates. Birds and land mammals, such as rodents and rabbits, are also taken.
Studies indicate that the fish consumed are mainly nongame species.
The straight-line length of a home range, including land area, was found to average about 15 km for adult males and 7 km for females with young. The ranges of males constitute territories, which may overlap the ranges of 1 or more adult females and from which other males are excluded. Females also defend their ranges against individuals of the same sex. Territories are marked with scent, and fights occasionally take place. Apparently, males form a dominance hierarchy, with the highest-ranking animals occupying the most favorable ranges.