Black-headed gulls

I went back to Blackford Pond to check on the swan family who all seemed well and still growing up fast.

There are other birds on the pond (coots, moorhens, tufted ducks, mallards and gulls) and I was intrigued by what these black-headed gulls were up to - couldn't really work it out. Maybe it's some kind of display, or warning other gulls off. They were certainly being quite quarrelsome today.