Populations of diurnal tree squirrels in the Portland area were located by mail surveys, personal interviews, and field inspections. Pine squirrels were found to reside in thickly wooded residential areas with dense understories and running water nearby. Western gray squirrels occupied habitats in relatively quiet residential neighborhoods, in areas well supplied with mast crops. Western fox squirrels were found to coexist with gray squirrels in their preferred habitat, and also to thrive in park settings with few mast trees and high activity and noise levels. In areas occupied by both fox and gray squirrels, dominant-subordinate relationships were noted. Each species tolerated the others.