Possible Cassin's Kingbird. East Grove, Torrey Pines State Park, San Diego, CA. Feb 2005. Canon 10D. I took several pictures of this bird, at the extreme range of my 300MM zoom. The overall grayness of the day made it hard for me to even manually focus on this bird at that range. Looking through all the pics, and knowing that the yellow belly and dark tail were quite striking--it's what caught my eye and made me take the picture--and after pouring over my bird books for what seemed like hours, Cassin's Kingbird is my best guess. Boy, Cassin has a lot of birds named after him/her? Who was Cassin? More research to follow...