This is a video about a juvenile white-winged black tern, in Hyde Park, London, Britain.
From Wildlife Extra:
Stunning White-winged Black Tern graces Cleveland Lakes Reserve, Cotswold Water Park
White-winged Black Tern sightings
July 2012. On what was expected to have been a routine monitoring visit for breeding waterbirds at the Cotswold Water Park Trust’s Cleveland Lakes Reserve, Tuesday 27th June “terned” out to be anything but routine for CWP Trust volunteer, Kim Milsom. Kim was greeted by the sight of an adult White-winged Black tern feeding over the reserve, flashing black and white with each wing beat.
More notable sightings
This is just the latest in a series of notable bird sightings for this reserve in recent years, following birds such as Glossy Ibis, Spoonbill, Great White Egret, Tawny Pipit and Osprey. This site continues to produce good numbers of migrating waders, terns and gulls each year, comprising the best and most important feeding grounds for these birds in the Cotswold Water Park and this part of the Upper Thames valley.
White-winged Black Terns have been sighted in CWP on a number of occasions in the past, but sightings are usually of juveniles in the autumn. A stunningly plumaged adult is a rare, but very welcome, surprise for local birders!