Pale crag martin to do so, it would cast doubts on their specific distinctness. There are several subspecies differing in plumage shade or size, although the differences are clinal, and races interbreed where their ranges meet. The pale crag martin of the nominate subspecies "P. o. obsoleta" is 12–13 cm (4.7–5.1 in) long with light brown upperparts, becoming paler on the lower back, and a short square tail that has small white patches near the tips of all but the central and outermost pairs of feathers. It has a pale grey throat, upper breast and underwing coverts, and the rest of the underparts
A Whiter Shade of Pale phrase stuck in his mind. The original lyrics had four verses, of which only two are heard on the original recording. The third verse has been heard in live performances by Procol Harum, and more seldom also the fourth. Claes Johansen, in his book "Procol Harum: Beyond the Pale", suggests that the song "deals in metaphorical form with a male/female relationship which after some negotiation ends in a sexual act". This is supported by Tim de Lisle in "Lives of the Great Songs", who remarks that the lyrics concern a drunken seduction, which is described through references to sex as