Gull with tennis ball

Cycling home this afternoon I spotted a seagull playing with a tennis ball that it had found floating in the Thames just by Houses of Parliament.
The gull was chasing the ball around the pavement with its beak trying to pick it up and carry it back up to his pal who was watching from the embankment wall. Problem was that the top of the wall slopes down and the ball once up there, rolled back down onto the pavement. Several passers by obligingly kicked the ball back to the gull and so the game continued until the gull realised it was surrounded by photographers, stood very still and flew off.
I placed the ball back onto the wall in case it returned once the photographers retreated.