ID trouble-- pelagic bird
I'm new to the list, so I apologize in advance if this question is inappropriate or just plain dumb. This weekend I was on San Francisco bay and saw a pelagic-type bird that behaved like a storm-petrel, padding its feet on the surface of the water while hovering. The tail was more wedge-shaped than forked. However, it was bigger than a storm-petrel should be, about the size of a small gull. The feathers were mottled brown, white, gray. In fact, it looked somewhat gull-ish, except for the strange behavior and a wider tail. Do any other birds perform the foot-paddling behavior? I checked Sibley, National Geo, but didn't find any answers.
San Francisco, CA