Although primarily nocturnal, it is active day and night throughout the year and solitary, except for a brief period during the breeding season. About one week after a female gives birth, she breeds again. Because fisher seldom travel in open areas and tend to be nocturnal, they are rarely seen by humans. They have not been studied as extensively as many other wildlife species because they are difficult to observe. Home range estimates vary, ranging from three to 15 square miles and averaging four to eight square miles in suitable habitat.
Males range over larger areas than females.
Fisher also use tree cavities as non-natal dens and will den or rest in the thick growth of conifer trees and in tree nests of squirrels or large birds. They are known to use ground cavities such as rock crevices in winter. Fisher hunt by zig-zagging through areas of thick, regenerating forest vegetation, but they traverse areas with little ground cover in a relatively straight line, hardly changing direction. Capable climbers, fisher often investigate large trees that might harbor prey, such as squirrels, that den or nest in trees. They do not stalk or chase prey but rely on surprising their quarry.