Swift; Vencejo Común

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 Swift (Common Swift is sometimes used) has darker wings which show very little light from below and usually only has an indistinct white patch on the chin. It is rarely possible to be absolutely certain with pictures such as these.