Mostly nocturnal and crepuscular, some diurnal activity. The long axis of home range tends to parallel valleys. May. Litter size averages 2.7, and ranges from 1-4, rarely 5. Young remain with female until late autumn. Few animals prey on fishers other than humans.
Fishers are one of the few specialized predators on porcupines.
A radiotelemetry study of fishers in northwestern California. Clem, M. K. 1975. Interspecific relationship of fishers and martens in Ontario during winter. Pages 165- 182 in R. L. Phillips and C. Jonkel, eds. 1975 Predator Symposium.