Description
The adult African River Martin is a large swallow, 14 cm (5.6 in) long. It is mainly black, with a silky blue-green gloss to the head, becoming distinctly green on the back and wing coverts. The underparts, other than the brownish under-wings, are purple-black, and the flight feathers are black. The black square tail is 4.8 cm (1.9 in) long, and the soft feather shafts project beyond the barbed section. This feature is most pronounced in the two central feathers, which in the related White-Eyed River Martin are greatly elongated. The African River Martin has brown legs with a 1.5 cm (0.6 in) long tarsus, red eyes, pink eye-rings, and a broad orange-red bill. The wing length averages 14 cm (5.6 in).
The sexes are similar in appearance. There are many bird species in which there is sexual dichromatism which is not apparent to the human eye, but spectroscopic analysis of this martin's head feathers suggests that the colour differences between the sexes are small even to the birds' perception. Juveniles are duller and have sooty brown heads. The moult to adult plumage takes place in the wintering areas and is largely complete by October.
The African River Martin has a strong, fast flight interspersed with glides. It is a vocal species with a variety of sounds. It has a jingling song given in the aerial breeding display, and a number of contact calls, kee-r-r, chee-chee and similar short, unmusical sounds. Flocks call together, cheer-cheer-cheer, as they take to the air, and this martin is very vocal during migration, giving harsh gull-like calls.
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