Food resources and diet composition in riparian and upland habitats for Sitka Mice, Peromyscus keeni sitkensis

Food resources and diet composition of Sitka Mice, Peromyscus keeni sitkens is, were studied over a four-year period in four floodplain and upland fore st habitats: old-growth Sitka Spruce (Picea sitchensis) floodplain; Red Ald er (Alnus rubra) floodplain; Beaver (Castor canadensis)-pond floodplain; an d nearby old-growth Sitka Spruce-Western Hemlock (Tsuga heterophylla) uplan d forest. Food resources in each habitat were quantified in terms of unders tory biomass and species richness, fruit production, tree seedfall, and rel ative abundance of arthropods. Diet composition was analyzed from stomach c ontents. Between-year differences in the availability of food resources wer e substantial, but between-habitat differences were minor. Diet composition differed between years and between months within years but did not differ between habitat types or age and sex classes of mice. We conclude that floo dplain habitats do not provide unique food resources for Sitka Mice in comp arison to upland old-growth forests. However, spatial and temporal complexi ty within habitats is an important feature of habitat quality in floodplain forests for Peromyscus mice.