Xavi Bou’s series has so far been made entirely in Spain. Far left, griffon vultures’ trails form a tornado in Valderobles. Top: three European herring gulls off the coast of Barcelona; and a group of common swifts above the same city, below. Bou aims to capture skies which have colour and texture, providing interesting backdrops to each flight path: “Talking about skies, I especially like the moment which comes just after the sunset, for instance—but I also love fog scenes.”