OK, I'll stick my neck out. Its somewhat dumpy appearance and largish head make me think this is quite a small bird. I thought it might be an empidonax flycatcher in the first photo based on the overall structure and coloration, but was not sure which species. I was thinking possibly "Western" or Hammond's, although the primary projection looks a little short for Hammond's and its head does not appear to be a contrasting gray. After today's photo, I think it might be a Buff-breasted based on the buffy coloration on the face and around the undertail coverts. The primary shape and projection looks OK for that species too. Also, it's cheating a bit, but from what I can tell of the background and the twig it's sitting on, it looks like it might be in an Apache Pine. I am bothered a bit by the fact it's not showing much of an eye-ring, but that could be based on the angle. I think even from this angle, it would show more eyering if it was a "Western" type. Then again, maybe I'm completely off the mark!