They eat primarily conifer seeds and fungi. They also consume pollen cones and cambium of conifers, mast, twigs, sap, leaves, buds, and occasionally arthropods, bird eggs, and nestlings. They forage in trees and on the ground.
Food is cached, often in large caches, for winter use.
These caches are located in moist places in trees, or under logs, stumps, rocks, or litter. Individuals may tunnel under snow to reach caches. They tend to avoid areas with considerable shrub understory. Douglas' squirrels breed in mature conifer stands. Nests are located in cavities in trees and snags, often old woodpecker nests, or occasionally in rock cavities.