A common resident of old growth coniferous forests in the Pacific Northwest, Douglas squirrels are active during the day and often heard chattering alarm about passing hikers. They spend summer nights sleeping in nests made among the tree branches, but during winter will instead nest in holes that provide more warmth.

They are territorial and usually solitary, although mated pairs will jointly defend a shared territory during the mating season. Groups of squirrels seen together are usually youngsters from the same litter.

They mostly eat the seeds of coniferous trees such as Douglas fir, but will eat a wide range of other foods (acorns, berries, mushrooms, eggs, and some fruit) as needs must. Each squirrel hoards food in a single location, building up a giant pile of discarded pine scales (up to several meters across!) after years of methodically stripping down one pine cone after another to get to the seeds inside.