White-eyed River Martin

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. However, distinct differences in foot and toe morphology from its African relative have led some authorities to speculate that even the assumption that it nests in burrows could be incorrect. In winter, it roosts with barn swallows in reed beds. 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. Pamela C. Rasmussen suggested that, given its unusually large eyes, the species might be nocturnal or at least crepuscular, a factor that could make it very inconspicuous, and thus partly explain how it remained undetected for so long. Although the fact that the first specimens were supposedly collected roosting at night in reedbeds might appear to contradict this theory, it is possible that the birds might not have been caught at the roost. Alternatively, they might be capable of both diurnal and nocturnal behaviour, or be crepuscular, depending on the season or circumstance.

The white-eyed river martin was discovered in 1968 by 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. It was first seen in the wild by ornithologists at the same wintering site in 1977. The species has only been seen at the lake, 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 reed beds for the night-time roost. The white-eyed river martin may be migratory, and 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 breeding grounds and habitat are unknown, although river valleys in northern Thailand or southwestern China are possibilities. A claimed depiction of this species in a Chinese scroll painting initially appeared to support the possibility of the martin breeding in China. The bird in the painting had a similarly shaped head and bill, a white eye and a long tail, although it lacked the white rump, did not show the correct bill colour, and elongated the outer, rather than central, tail feathers. Painted before 1970, it pre-dated the publication of pictures of the Thai bird, so it must have been painted from life. It is now thought more likely that the scroll shows Oriental pratincoles (Glareola maldivarum). Cambodia and Burma have also been suggested as possible refuges for the martin, but there has also been speculation on whether it is migratory at all.

The white-eyed river martin was seen in Thailand in 1972, 1977 and 1980, but not definitely since, although 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, and was probably always rare. There has been a drastic decline in the Bueng Boraphet swallow population from the hundreds of thousands reported to roost 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 hunting. Other potential causes for the martin's decline include the disturbance of sand bars in the rivers, and the construction of dams (which flood the area upstream and change the water flow downstream), deforestation, and increasing conversion of its habitat to agriculture. Other Southeast Asian species using riverine sand bars have also been adversely affected by disturbance and habitat degradation. Very few swallows of any kind now roost in the Bueng Boraphet reedbeds, preferring sugarcane plantations, and, despite searching, the white-eyed river martin has not been found in other nearby large swallow roosts. The martin is legally protected under Appendix 1 (the highest category) of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) agreement, and is one of 15 "Reserved Species" in Thailand which, under the provisions of the Wild Animal Reservation and Protection Act, BE 2535, cannot be legally hunted, collected, or kept in captivity under any circumstances. Despite official protection, the martin was captured by locals along with other swallows for sale as food or for release by devout Buddhists, and following its discovery by ornithologists, trappers were reported to have caught as many as 120 individuals and sold them to the director of the Nakhon Sawan Fisheries Station who was unable to keep them alive in captivity. Two birds sent to Bangkok Zoo in 1971 also soon died. The small population may therefore have become non-viable. Bueng Boraphet has been declared a Non-Hunting Area in an effort to protect the species, but surveys to find this martin have been unsuccessful. These include several searches at the main site, a 1969 survey of the Nan, Yom and Wang Rivers of northern Thailand, and a 1996 survey of rivers in northern Laos. A possible sighting was made in Cambodia in 2004, but a 2008 investigation using speedboat surveys and interviews with villagers in Cambodia near the location of the claimed sighting failed to find any positive evidence, and noted that the habitat was in poor condition. Nevertheless, animals as a large as the saola have been rediscovered in Southeast Asia, so it is conceivable that a small population of the martin survives. Despite the lack of records from China, a 2000 field guide covering the region included this species, since it is the mostly likely breeding area outside Thailand, although it is omitted from the 2008 Birds of East Asia. The white-eyed river martin and the Deignan's babbler, Stachyridopsis rodolphei, are the only bird species endemic to Thailand, and the martin has attracted sufficient interest to be featured on a 75 satang postage stamp in 1975, as one of a set of four depicting Thai birds, and on a 5,000 Thai baht conservation issue gold coin in 1974.