This is an example of the kind of thing that's very difficult to photograph with a 500mm lens. Unless you've fitted it with some kind of sighting aid. This was taken with the aid of a red dot gun sight fitted to the lens barrel. I was catching such shots almost every time a gull flew past, whereas without it I'd manage to catch maybe one in twenty.
Apart from that technical interest it's a crap photo taken on a seriously overcast misty day. I include this unprocessed image to show what it looked like in the finder. It crops down and polishes up fairly well, but of course not a patch on what could have been done with better light.