I got a quick response from John Herring who saw and photographed the
Brown Booby yesterday. Turns out it was nearer to and just EAST of the Ballard
Bridge, NOT the I-5 Ship Canal bridge.

In response to my query, John writes:
"The bird was floating in the middle of the ship canal, about a quarter
mile east of the Ballard Bridge. Having nothing other than a pocket camera I
was crowding him to get a decent shot, so I chased him into flight. He
was westbound when I last saw him but I think he landed again near the bridge.
Did not see any feeding or other behavior, just resting on the water until
spooked. No other birds around him. This was just shortly before noon
yesterday, 9/11."

Richard Rowlett
Bellevue (Eastgate), WA