This video from the Netherlands is called Sandwich Tern chick preening.
From the Norfolk Coast National Trust blog in England:
21 June 2015
Over the past two weeks, we have seen an influx of late-arriving Sandwich Terns. Today, a total of 314 new nests were counted on the tip of Far Point alongside Common and Little Terns. This year, we are continuing our research into the factors affecting Little Tern breeding success, which involves the use of trail cameras on nests.