Although largely terrestrial, these weasels are adept at climbing trees. They are strong swimmers and do not hesitate to cross swift streams. On the ground they frequent areas occupied by small rodents and often live in the burrows of ground squirrels and pocket gophers or in rotten logs, hollow stumps, and under tree roots. Their nest is made of grass and leaves and is lined with rodent and rabbit fur. They may have more than one home.
Weasels are active both in the daytime and at night, but more so after dark.
They are apparently unafraid of man and have a strong sense of curiosity. Davis once observed one watching him with only its head projecting from the burrow of a pocket gopher. When he approached, it withdrew and reappeared at another opening about 7 m farther on. His closer approach again caused it to retreat and reappear at a third opening. By imitating the distress call of a bird, Davis was able to attract weasels to within 10 m of him.