One of the things seagulls do as a way of sending out an "alarm" when they feel like their may be a threat close is to start cawing. This is a loud, repetitive sound they make. I was on a little dock one morning off of the South Jetty road here in Florence, Oregon and I came up on two birds. As I got a little closer, they both started to sound the alarm. One of the things I try to do with my wildlife shots is photograph them doing something natural that they do all the time. For seagulls, cawing is something they do quite often.