This is a video of White-winged terns in winter plumage.
From NOS TV in the Netherlands:
There is a breeding bird species, new to the Netherlands: the white-winged tern. Eight young terns have hatched in the Krimpenerwaard and the Sliedrechtse Biesbosch for the first time ever.
White-winged tern in Sliedrechtse Biesbosch: video here.