Great Crested Grebes and a raiding gull

A Great Crested Grebe chick on the Long Water is being fed by its father when a Black-Headed Gull swoops down and tries to grab the fish.

[michaelsimko]

Typical of a Gull to do that to birds such as Grebes, Loons, Cormorants, and Mergansers. Gulls will even chase Terns, Ospreys, and other Gulls to try and get access to the food the bird is carrying.