Importance of Tree Cavities as Natal Dens for Fishers

We determined characteristics of natal dens used by radio-collared fishers in southcentral Maine. Twelve adult (≥2 yr old) females were monitored for periods of 1-5 yr each during 1984-1989. Estimated whelping dates of 12 litters were March 3-April 1, and females used 1-5 natal dens each until denning ended in early June. All 33 natal dens were in tree cavities on upland sites. Hardwoods composed 94% of the den trees, with aspens accounting for 52%. We recommend that forestry practices allow for a continued supply of mature and decadent hardwoods > 40 cm dbh to replace cavity trees that fall. Where cavity trees must be removed, cutting should be done outside the March-June denning period to avoid disturbance or mortality of fisher litters. North. J. Appl. For. 13(2): 79-83.