Whatbird.com

What kind of bird is this:  http://www.youtube.com/watch?v=E0dZH-iKz48 ?  I found it on the beach in Pensacola Beach, Fl, and have seen them a few times.  They kind of flop up on the shore and just lay there like they are injured, but they aren't actually sick or injured at all.  Their legs are really far back too.

Unknown accipiter --can anyone give clues without a photo?  Its solid medium gray underside and lack of underside barring or streaking has us puzzled. SEEN:  06-12-08  7 p.m. Suburb of North Indianapolis Indiana backyard --standing on the ground with grackles and robins diving and screaming at it.  This area has some ...