This video says about itself:
12 May 2017
The Swift is one of Ireland‘s most special migrant birds, visiting Irish towns and cities for just three months each summer to nest and raise their chicks. The rest of lives of the Swifts breeding in Ireland are spent entirely on the wing, high in the skies of Africa.
They are among nature’s best fliers, spending most of their time in flight. Now scientists have shed new light on how swifts can glide with ease, whatever the weather: here.