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
Pale Fire are many resemblances to "Ultima Thule" and "Solus Rex", two short stories by Nabokov intended to be the first two chapters of a novel in Russian that he never continued. The placename Thule appears in "Pale Fire", as does the phrase "solus rex" (a chess problem in which either colour has no pieces but the king). The book is also full of references to culture, nature, and literature. They include: See also "The Ambidextrous Universe", a later book referencing "Pale Fire" which in turn triggered a reciprocal response in a subsequent Nabokov novel ("", 1969). Pale Fire Pale Fire is