That is really early. I've been trying to learn Gull. I am really good at Herring Gull and know many of their calls. Downtown last week when I was feeding Gulls with ' Mini Cheddars ' a Black Backed Gull (lesser) swooped and stole some young girl's Pizza Slice. I clearly heard the Herring Gulls scream " You thieving bastard, that's just a young human " The BBG screamed back, it sounded more like a Common Tern or possibly an Artic Skua. This was strange as usually the BBG sounds quite similar to the Herring Gull. I was just wondering if a book or video is available on this subject ?