THE FOOD HABITS OF FISHERS (PEKANIA PENNANTI) IN THE CASCADE RANGE OF SOUTHERN OREGON

Abstract The Fisher (Pekania pennanti) is a mesocarnivore of conservation concern in the Pacific coastal region of North America with a diverse but poorly understood diet. From 1995 to 2001, we collected 297 scats from 11 radio-collared females and 83 scats from 8 radio-collared males, and used frequency of occurrence (percentage of scats containing a particular food item) to investigate their diets. Mammals were the most frequently occurring food item in the diets of both female and male Fishers (84.8 and 77.1 % of scats, respectively); however, the prevalence of small (≤166 g) mammalian prey was relatively low (<13% of female and <9% of male scats). Medium (191–579 g) and large (643–1710 g) mammalian prey were 6.6 and 2 times more prevalent, respectively, in the diet of females compared to males, and very large prey (≥2085 g) were almost 26 times more prevalent in the diet of males. Female Fishers are about 50% smaller than males and may be less effective than males at capturing very large prey. However, in the diet of females raising kits, leporids (large prey) and ground squirrels (medium prey) were 3 and almost 2 times more prevalent, respectively, than they were among females with no kits. Focusing on such prey would provide more metabolic energy per capture than mice, voles, and other small mammals, and require fewer hunting forays away from kits. Thus, our findings show that sexual dimorphism and female reproductive condition influence the diet of Fishers in the Cascade Range of southern Oregon. Studies that use molecular techniques to identify food items in scats that were collected with a rigorous sampling design that enables researchers to link Fisher diets with correlates of fitness are needed to determine the extent to which food habits influence Fisher population dynamics in this region.