Cassin's Kingbird (Tyrannus vociferans) - 30Mar2016

Per the Cornell site: "A large, noisy, and conspicuous flycatcher of the southwestern United States and Mexico, the Cassin's Kingbird can be distinguished from the other yellow kingbirds by its dark gray head and chest, and the white tip to its black tail."

Here is a pic from Mission Bay in San Diego, CA while I waited to board a whale watching trip.