Pallid Swift; Vencejo Pálido

Large numbers of Swifts were flying over, some were obviously Alpine but the rest were a mix of Pallid and Common Swift, the differences being difficult to see but some were clearly paler and browner to the eye than others. The Pallid Swift has paler wings which show very light from below as they allow a lot of sunlight through and when they fly close to the ground it is possible to see a pale brown on top of the wings. They also have a clearly white chin and throat as seen in the first picture which also shows clearish wings.