Fight Club!

These two sand martins Riparia riparia were involved in a battle royal on the beach below the colony in the face of a sand dune. I imagine that they were involved in a dispute over ownership of a nest tunnel in the dune face. It was a vicious no-holds-barred fight. So occupied were they, with their attempts to kill each other, that I was able to take the photograph from a distance of some  6 inches!
As you can see, one of them, the one coming off worst, was a ringed bird.