Temporal partitioning among sympatric forest carnivores drives a temporal mismatch with preferred prey

Abstract Interspecific competition is a driving force behind animal distribution and behavior. Competition is especially strong among phylogenetically related carnivores that share prey and habitats. Competitors can reduce overlap by partitioning time; however, adjusting activity patterns to avoid competition can potentially alter their access to prey. American martens (Martes americana) and fishers (Pekania pennanti) are competing species that overlap throughout much of their distributional range, though American martens are more adapted to deep snow conditions. We sought to understand the effects of competition, snow conditions, and prey activity patterns on American Marten and Fisher temporal activity. We used a combination of camera and live-trapping data to explore the activity patterns of American Marten and Fisher as well as their small mammal prey (rodents and soricids). Fishers exhibited largely nocturnal behavior, regardless of American Marten activity. We found that American martens showed increased activity during the day at sites where fishers were present, even during deep snow conditions. In the absence of their sympatric competitor, both species were active at the same time as rodents, but American martens overlapped more with lower-quality soricid prey where fishers were present. Our work reveals how interference competition and prey activity interact to influence the diel activity of competing carnivores. In particular, the subordinate carnivore seems to respond more strongly to competition than to the activity of preferred prey. Our work supports the concept that fishers alter the fundamental ecological relationships of American martens, which is likely contributing to the slow recovery of American martens in some areas.