African River Martin - Taxonomy

Taxonomy

When German zoologist Gustav Hartlaub first described the African River Martin in 1861, it was not initially thought to be a member of the swallow and martin family, and he placed it with the rollers. Later authors either placed it in its own monotypic family, or with the woodswallows. A 1938 study of this martin's anatomy by Percy Lowe revealed that the species was closest to the swallows and martins, but sufficiently distinct to be placed in a separate subfamily, Pseudochelidoninae.

The only other member of the subfamily is the White-eyed River Martin Pseudochelidon sirintarae, known only from one site in Thailand and possibly extinct. These two species possess a number of features which distinguish them from other swallows and martins, including their robust legs and feet, stout bills, large syrinxes (vocal organs) and different bronchial structure. Genetic studies confirmed that the two river martins form a distinct clade from the typical swallows in the Hirundininae subfamily.

The two river martins are in some ways intermediate between typical swallows and other passerines, and the arrangement of their leg muscles is more like that of a typical passerine than of a swallow. The extent of their differences from other swallows and the wide geographical separation of these two martins suggest that they are relict populations of a group of species that diverged from the main swallow lineage early in its evolutionary history. Like other early hirundine lineages, these martins nest in self-excavated burrows, rather than adopted nest holes or mud nests. Their physical characteristics and breeding behaviour suggest that they may be the most primitive of the swallows.

The genus name Pseudochelidon (Hartlaub, 1861) comes from the Ancient Greek language prefix ψευδο/pseudo, meaning "false," andχελιδον/chelidôn, meaning "swallow." The species name reflects the superficial similarity to the rollers of the genus Eurystomus.

The African and Asian Pseudochelidon species differ markedly in the size of their bills and eyes, suggesting that they have different feeding ecologies, with the White-eyed River Martin probably able to take much larger prey. The African species has a softer, fleshier, and much less prominent gape (fleshy interior of the bill) than its Thai relative. The bill of the White-eyed River Martin also averages 22.5% wider than that of the African River Martin. Following a suggestion by the Thai bird's discoverer, Kitti Thonglongya, Richard Brooke proposed in 1972 that the White-eyed River Martin was sufficiently different from the African species to be placed in a separate genus Eurochelidon, leaving the African martin in a monotypic genus. This treatment was contested by other authorities, and most authors retain the two species in Pseudochelidon, BirdLife International being a notable exception.