Western kingbirds are noisy, aggressive, obvious birds that breed across much of western North America.  They can be identified by their chattering calls, 'kingbird' posture, gray head, yellow breast, black tail, and narrow white outer tail feathers (visible in a couple of these images and a key field mark for separating this species from the closely related Cassin's kingbird).   I these photos at a campground on the northeast shore of the Salton Sea in southeastern California.
            This page has images of western kingbirds at rest.