This video was made by Frank van der Meer, at a rubbish tip in Barneveld, the Netherlands.
Among many black-headed gulls (winter plumage, so mostly white heads) and some (bigger) herring gulls: two gulls, rare for western Europe. They are Caspian gulls. First, a young bird, not yet one year old. Later, an adult Caspian gull (red circle around the eye, dark iris).