Marten (Martes americana) experience greater survival and production rates in old growth forests than in postclear-cut forests. To determine whether total time active and foraging success contribute to these differences, we compared marten movements and hunting activities in their preferred old-forest habitats to those in logged forests. Marten in uncut forests captured up to 119% (P = 0.003) more prey biomass than those in logged forests, depending on prey populations. We found few marten activity differences by forest type attributable to differences in density and prey species, or habitat structure. Distances between core areas in individual home ranges were greater (P