Taxonomy
The Pale Crag Martin was first formally described in 1850 by German ornithologist Jean Cabanis as Cotyle obsoleta, using a specimen collected from near Cairo, Egypt. It was moved to the new genus Ptyonoprogne, created by German ornithologist Heinrich Gustav Reichenbach, in the same year. The genus name is derived from the Ancient Greek ptuon (φτυον), "a fan", referring to the shape of the opened tail, and Procne (Πρόκνη), a mythological girl who was turned into a swallow. The specific name obsoleta means "worn" in Latin.
The Ptyonoprogne species are members of the swallow family of birds, and are classed as members of the Hirundininae subfamily, which comprises all swallows and martins except the very distinctive river martins. DNA sequence studies suggest that there are three major groupings within the Hirundininae, broadly correlating with the type of nest built. These groups are the "core martins", including burrowing species like the Sand Martin; the "nest-adopters", which are birds like the Tree Swallow that utilise natural cavities; and the "mud nest builders". The Ptyonoprogne species construct open mud nests and therefore belong to the last group. Hirundo species also build open nests, Delichon house martins have a closed nest, and the Cecropis and Petrochelidon swallows have retort-like closed nests with an entrance tunnel.
The genus Ptyonoprogne is closely related to the larger swallow genus Hirundo, and is sometimes included within it since the nests of the Ptyonoprogne crag martins resemble those of typical Hirundo species like the Barn Swallow. However, a DNA analysis showed that if Hirundo is enlarged to contain the crag martins, it should include all the mud-builder genera. Conversely, if the Delichon house martins are considered to be a separate genus, as is normally the case, Cecropis, Petrochelidon and Ptyonoprogne should also be split off. The Pale Crag Martin's nearest relatives are the other members of the genus, the Dusky Crag Martin P. concolor of southern Asia, the Rock Martin P. fuligula of Southern Africa, and the Eurasian Crag Martin P. rupestris.
The Pale Crag Martin was formerly often treated as the small, pale northern subspecies of the Rock Martin, but it is now usually considered to be a separate species. The changes in size and colour are continuous, so the evidence for separate species is not strong, although some Rock Martins can weigh more than twice as much as the smallest subspecies of the Pale Crag Martin. The average weight for P. o. fusciventris is 22.4 g (0.79 oz) against 10 g (0.35 oz) for P. o. obsoleta. There do not appear to be any intermediate forms where Pale Crag Martins and Rock Martin populations breed close to each other in Somalia and Ethiopia.
In areas of Pakistan where its range overlaps with that of the Dusky Crag Martin, the Pale Crag Martin breeds at a higher altitude. Its range does not overlap there with the Eurasian Crag Martin, which is found high in the Himalayas, but where both occur in Iran, the Pale Crag Martin favours more arid habitats. In North Africa, the Eurasian species is again found at a higher level. The separation by altitude and aridity means that it is not known whether the closely related Ptyonoprogne martins could hybridise. If they were shown to do so, it would cast doubts on their specific distinctness.
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