African river martin

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 from them 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. The two river martins are in some ways intermediate between typical swallows and other passerine birds, 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. 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", and χελιδον/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 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 river 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. ==Description==

The adult African river martin is a large swallow, 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 long, 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. ==Distribution and habitat==

The African river martin breeds along the Congo River and its tributary, the Ubangi in the Democratic Republic of the Congo (DRC), an area estimated at 47,000 km2 (18,150 mi2). Westwards migration from the DRC is from June to early September, with birds arriving at the coast from mid-August to mid-September. Return migration is mainly from December to March. Three or four birds were seen passing through the southern Central African Republic in 1994. The main coastal breeding area in Gabon, around Gamba, has a similar mosaic of habitats, with mangroves, swamp forests, wet evergreen woodlands and seasonally wet savanna. There are also two large lagoons, and drier areas of grassland and forest. All the breeding areas form part of a belt of forest that stretches from southern Cameroon through Gabon to the northern parts of the Republic of Congo, and extends through most of the DRC up to its eastern mountains. Outside of the breeding season, this martin roosts in reed-beds or riverine vegetation. ==Behaviour==

The African river martin has flight displays in which pairs or small groups chase each other while making jingling calls. It also displays on the ground, with the wings drooped and slightly open, and the head raised but held horizontally; the function of these terrestrial displays is uncertain. This species nests in colonies in sandbanks along forested rivers from December to April when the river is low. The colonies, sometimes shared with rosy bee-eaters in Gabon, may contain up to 800 birds, each pair excavating a long tunnel in the sandbar. Two to four unspotted white eggs are laid onto a few twigs and leaves in the pocket at the end of the tunnel. The eggs measure . The incubation and fledging times are unknown, although it is believed that both parents care for the nestlings. Wintering birds dig tunnels in the sand in which to roost overnight. ==Status==

The total population size of the African river martin is unknown. In the late 1980s, it appeared to be common, if local, and large numbers were seen on migration in Gabon. However, it is particularly poorly studied in the Democratic Republic of the Congo (DRC), and it is not known if there is any relationship between the birds breeding in the DRC and those breeding in coastal areas of Gabon and Congo. Several hundred birds were seen at Conkouati-Douli National Park in Congo in 1996 and a flock of 15,000 birds was seen in Gabon in 1997. and a mixed flock with rosy bee-eaters at Loango National Park in Gabon was estimated at 100,000 birds in total. and Gabon (''Loi d'orientation en matière des eaux et forêts, 1982 and Loi relative à la protection et à l'amélioration de l'environnement'', 1993), and by regional legislation in Nigeria, which does not have national wildlife laws. The Nigerian laws are based directly on older colonial era laws which include a number of species, such as this martin, which are not native to the country. In the 1950s, this martin was caught and eaten in large quantities in the DRC by the local population, and this practice could be increasing. Breeding colonies in river sandbars are liable to flooding, ==References==