The White-eyed River Martin (Pseudochelidon sirintarae, sometimes Eurochelidon sirintarae) is a passerine bird, one of two members of the river martin subfamily of the swallow family Hirundinidae. It is known only from a single wintering site in Thailand, and may be extinct since it has not been seen since 1980.
The adult White-eyed River Martin is a medium-sized swallow, with mainly glossy greenish-black plumage, a white rump, and a tail which has two elongated slender central tail feathers with long narrow racquets at the tips. It has a white eye and a broad, bright greenish-yellow bill. The sexes are similar, but the juvenile lacks the tail racquets and is generally browner than the adult. Little is known of the behaviour or breeding habitat of this species, although like other swallows it feeds on insects caught in flight, and roosts in reedbeds in winter.
As a Thai endemic, this bird was featured on a 75 satang postage stamp in 1975 as one of a set of four depicting Thai birds, and on a 1974 5,000 baht conservation issue gold coin.
The White-eyed River Martin is one of two members of the river martin subfamily Pseudochelidoninae, the other being the African River Martin (Pseudochelidon eurystomina) of the Congo basin in Africa. These two species possess a number of distinctive features which mark them out from other swallows and martins, including their robust legs and feet, and stout bill. 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 evolution.
The genus name Pseudochelidon (Hartlaub, 1861) comes from the Ancient Greek prefix ?????/pseudo "false" and ???????/chelid˘n, "swallow", and the species name commemorates Princess Maha Chakri Sirindhorn of the Kingdom of Thailand.
The African and Asian Pseudochelidon species differ markedly in the size of their bills and eyes, suggesting that they have different feeding ecologies, with White-eyed River Martin probably being able to take much larger prey. The Thai species also has a swollen, hard gape (fleshy interior of the bill) unlike the soft, more fleshy, and much less prominent gape of African River Martin.
It was proposed in 1972 that the White-eyed River Martin was sufficiently different from the African species to be placed in a separate monotypic genus Eurochelidon, but this was not subsequently widely adopted by other authors; however, BirdLife International now uses Eurochelidon.
Distribution and habitat
The White-eyed River Martin was discovered as recently as 1968 by Thai ornithologist Kitti Thonglongya, who obtained nine specimens netted by professional bird-hunters as part of a migratory bird survey at a night-time roost at Thailand's largest freshwater lake, Bueng Boraphet in Nakhon Sawan Province.
The species has only been seen at that site, always between the months of November and February, and the wintering habitat is assumed to be in the vicinity of open fresh water for feeding, with reedbeds for the night-time roost. The White-eyed River Martin may be migratory, but its breeding grounds and habitat are unknown, although river valleys in Northern Thailand or southwestern China are possibilities; however, a claimed depiction of this species in a Chinese scroll painting is more likely to show Oriental Pratincoles (Glareola maldivarum). Cambodia and Myanmar have also been suggested as possible refuges for the species, but doubts have been cast on whether it is migratory at all.
If the breeding habitat resembles that of the African River Martin, it is likely to be the forested valleys of large rivers; these can provide sandbars and islands for nesting, and woodland over which the birds can catch insect prey.
The adult White-eyed River Martin is a medium-sized swallow, 18 centimetres (7 in) long and mainly black with a silky blue-green gloss and a white rump. The back is green-glossed black, and is separated from the similarly coloured upper tail by a narrow bright white rump band. The head is darker than the back, with a velvet-black chin leading to blue-green glossed black underparts. The wings are black, and the tail is green-glossed black with two elongated slender central tail feathers, up to 9 centimetres (3.5 in) long expanded slightly at the tips to give long narrow racquets.
The iris and eyelid are white, giving the appearance of a white eye ring, and the bill is broad, bright greenish-yellow with a black hooked tip to the upper mandible. The large, strong feet and legs are flesh-coloured. This species is silent when wintering, and its breeding vocalisations are unknown.
The sexes are similar, but the juvenile lacks the tail racquets, has a brown head and chin, and is generally browner than the adult. Juveniles taken in January and February were moulting their body feathers.
Since its breeding grounds are undiscovered, nothing is known about the White-eyed River Martin's breeding biology, although it is suggested that it may nest in burrows in river sandbars, probably in April or May before the monsoon rain raises water levels. In winter, it roosts with Barn Swallows in reedbeds.
Like other swallows, the White-eyed River Martin feeds on insects, including beetles, which are caught on the wing. Given its size and unusual mouth structure, it may well take larger insects than other swallows.. This species is described as graceful and buoyant in flight, and, like its African relative, appears reluctant to use perches, behaviour that, together with its unusual toe-shape and the fact that mud was found on the toes of one of the first specimens, suggest that this species may be relatively terrestrial.
The White-eyed River Martin was seen in Thailand in 1972, 1977 and 1980, but not definitely since, though there is an unconfirmed sighting from Thailand from 1986. It is classified as critically endangered, which is the highest risk category assigned by the International Union for the Conservation of Nature and Natural Resources (IUCN) for wild species. The designation means that a species' numbers have decreased, or will decrease, by 80% within three generations. The IUCN does not consider a species extinct until extensive targeted surveys have been conducted, but the White-eyed River Martin may well no longer exist in the wild.
Despite legal protection under Appendix 1 (the highest category) of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) agreement, it was captured by locals along with other swallows for sale as food or for release by devout Buddhists, and since more than 100 are known to have been taken, the small population may have become non-viable. However, a possible sighting was made in Cambodia in 2004.
There has been a drastic decline in the Beung Boraphet swallow population from the hundreds of thousands reported around 1970 to maximum counts of 8,000 made in the winter of 1980-1981, although it is not certain if this represents a real decline or a shift in site in response to persecution. Other potential causes for the species' decline include the disturbance of riverine sand bars, the construction of dams which flood the area upstream and alter the downstream hydrology, deforestation, and increasing conversion of its habitat to agriculture. Very few swallows now roost in the Beung Boraphet reedbeds, preferring sugarcane plantations, and despite searching the White-eyed River Martin has not been found in other nearby large swallow roosts.
Beung Boraphet has been declared a Non-Hunting Area in an effort to protect the species, but surveys to find this martin have been unsuccessful, including several at Beung Boraphet, a 1969 survey of the Nan Yom and Wang Rivers of northern Thailand, and a 1996 survey of rivers in northern Laos.