I counted eight perched on the East stand roof, 'watching' the game, at one point in the second half. There were another three circling around inside the stadium. It was during a substitution, so I didn't miss any part of the game.
We sit right under the WSU roof and there seems to be a huge flock up there most matches. They actually make a drumming noise with their feet. My son and his best mate have called it "The Seagull Apocalypse"