Diet of Fishers (Martes pennanti) at the Southernmost Extent of Their Range

Abstract

Fishers ( Martes pennanti ) in the mountains of California's Sierra Nevada occur at the southwestern margin of their distribution and inhabit different forest types with different potential prey than elsewhere in their range. Two typical fisher prey, the snowshoe hare ( Lepus americanus ) and the porcupine ( Erethizon dorsatum ), are absent from our Sierra Nevada study area. We characterized the diet of fishers in the southern Sierra Nevada by analyzing the content of 201 feces (44 males: 157 females) collected either from trapped animals or from the rest sites of radio-collared animals. Mammals were the most frequent food item; however, unlike previous reports, reptiles (20.4% of feces) and insects (55.7%) were major components of the diet. We also sampled 24 feces for the presence of spores of hypogeous fungi (false truffles) and found that 91.7% had spores representing at least six fungal species. Diversity of the diet was indicated by the fact that remains of no single family of animal or plant group were found in >22% of feces. The fisher is reputed to be a habitat specialist in the late-seral mixed conifer-deciduous forests of the western United States. Perhaps it is for this reason that our data depict the species as a dietary generalist, for whom it may be necessary to forage on many of the animal, plant, and fungal species that occur in and near mature coniferous habitat.