White-tailed Kite (Elanus leucurus)
Above and below: A White-tailed Kite soars over the Tijuana River mouth, California (10/7/2011).
A nice example of why it used to be called Black-shouldered Kite.
(That name now refers to the similar Australian species.)
Below: A White-tailed Kite hunting in the early morning near Monte Alban, Mexico (3/2008).