This partially obscured image, my only view of this bird, provided a kind of photo ID puzzle and I posted it as such to the local Santa Clara County birding list. I guessed the bird was a Cassin's Vireo, on the basis of the apparent "spectacles" pattern. A couple of experts, Al Jaramillo and Mike Rogers, suggested that it was a House Wren, with Al noting the "overall coloration, lack of face pattern and 'ghost' mottling on the breast." John Sterling then pointed out the tail barring barely visible between the oak leaf and branch, which clinches the House Wren ID.