An inhabitant of open forest, forest edge, and riparian zones, the Western Wood- Pewee is a widespread breeder in many of western North America's forested habitats. Its generalized foraging behavior and nest site selection reflect its common occurrence. This species is primarily a sit-and-wait predator, sallying from open perches and usually returning to the same or a nearby perch in pursuit of flying insects, especially flies, ants, bees, wasps, and beetles. Its nest is usually placed in the fork of a horizontal branch, from near ground level to high up in living and dead trees. Both parents feed the young. Although an "acceptor" of Brown-headed Cowbird (Molothrus ater) eggs, this wood-pewee is generally an infrequent host of cowbirds.
The Western Wood-Pewee and the nearly identical Eastern Wood-Pewee (Contopus virens) are closely related, and along with the Tropical Pewee (C. cinereus), are regarded as a superspecies by some taxonomists. The Western and Eastern wood-pewees are separated by range, with small areas of overlap, and can be distinguished by vocalizations. Although common throughout its breeding range, many aspects of Western Wood-Pewee biology are not well known, especially its habits during migration and winter. Populations appear to be declining overall. This species may suffer from loss of riparian habitat in the United States andfrom unknown changes on migration and wintering grounds.