Partitioning of habitat use and diel activity facilitate coexistence of sympatric carnivores during winter

Competitive interactions are common among sympatric carnivores and are largely caused by intraguild predation or interspecific killing. These agonistic interactions can be reduced if species successfully partition along one or more niche axes. We deployed camera traps for three winters to investigate the spatial and temporal occurrence and co-occurrence of two reintroduced, sympatric carnivores, American martens (Martes americana (Turton, 1806)) and fishers (Pekania pennanti (Erxleben, 1777)) in northern Wisconsin, USA. We investigated three potential mechanisms to facilitate their coexistence: spatial segregation, habitat and temporal partitioning. We found evidence of spatial partitioning of martens and fishers through their divergent habitat associations, but no overlap in habitat use between the two species. Habitat use of martens was associated with mature deciduous stands and dense lowland coniferous stands, while fishers were associated with mixed forest stands and human development. Our analysis of diel activity showed consistently overlapping nocturnal patterns for both species when they occurred alone. However, we found a significant difference in diel activity patterns of martens at sites where fishers co-occurred, compared to sites where fishers were absent. Our findings provide evidence of habitat divergence and diel activity shifts between martens and fishers, indicating reestablished trophic function through multi-niche partitioning.