Ed, tweeters,

I had a chance to observe the Caspian Terns on the rooftop of the Pier 90
building this afternoon (about 5 PM).
Counted 156 birds. Only saw the legs of 96 of them. Of these, non were
banded.
Did see some interesting behavior. Twice I watched courtship feeding. One
bird presenting a nice silvery fish to another bird.
Seven "pairs" (I assume they were pairs) were taking turns (or should that
be terns?) lying down on the rooftop and making scraping movements with
their feet (trying to scrape out a nest hollow which would have been more
successful if they'd been on a sandy substrate rather than a metal roof).
One pair copulating. Quite different from other species' copulations I've
seen (not knowing if this is typical for Caspian Terns): one bird standing
on the other bird's back for a good four minutes and performing five
"lengthy" (each 15 seconds at least) "cloacal kisses."

I'm no expert on this species, but it looks to me like some of these birds
are going to try and ignore gravity and nest on this roof. This ought to be
interesting. The roof slants about 15 degrees....

A good spot to observe from is the Magnolia Bridge. You're about level with
the roof, but you will need a scope for the finer details. If you're going
by car remember that the western-most part of the bridge is closed
(earthquake damage), but you can drive to the marina, park and walk back
onto the bridge. There's a sidewalk along the south side of it.

Martin Muller, Seattle