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Little known Oriental Bird: White-eyed River-Martin: 2

It seems that any rediscovery efforts should now be targeted away from Bung Boraphet, and indeed perhaps away from Thailand. How might we judge where best to look? What secrets have hitherto been disclosed that might help direct our search? Unhelpfully, the ecology of this bird remains almost totally unknown, and thus ornithologists have looked to its presumed relative, the African River-Martin, to provide clues. Since P. eurystomina feeds largely over both forest and open grassy country, nesting colonially in tunnels dug in sandbars of large rivers (14) it has been inferred that E. sirintarae possibly does or once did the same (4). However, the differently shaped toes might suggest otherwise (19). At least one of the initial specimens had mud or sand adhering to its claws, and while this perhaps suggests a terrestrial perching habit (6), most swallows occasionally do the same, especially when collecting nest material. Another clue: in holding cages used during the swallow ringing programme, the birds stood quietly in the corner of the cage in strong contrast to other swallows which move rapidly from perch to perch calling repeatedly (1).


White-eyed
River-Martin
(H.E. McClure)

In the unconfirmed report of 1980, individuals were flying after insects with some Barn Swallows and sometimes perching on the tops of trees (20). During the 1978 sighting they were apparently skimming the water surface, possibly to drink (10). While these accounts describe behaviour characteristic of most swallows, the only direct dietary evidence is the fragment of a large beetle found in the stomach of a specimen (1). This fact, along with the mandibular morphology of the species, implies that it consumes sizeable prey.

What about breeding season, distribution and migratory behaviour? Five of the nine specimens collected in late January and early February 1968 were immature (1); they were later termed juvenile, and some of the other material as subadult (2) (although this is not mentioned in the original description). A breeding site within Thailand was initially considered plausible on the grounds that so many of the type series were young (2). It has also been speculated that if nesting occurs in Thailand it is most likely to do so between March and April, as this coincides with the local nesting season for the majority of insectivorous birds, while the monsoon rains from May onwards presumably raise water levels above the riverine sandflats postulated to be the favoured nesting habitat of the species (5,6,10). It is unlikely, however, that juvenile plumage would be retained for eight months, and thus these two facts are difficult to reconcile. The White-eyed River-Martin has otherwise been thought a non-breeding visitor to south-central Thailand (20) and clearly migratory (4), but these assumptions should also be treated with care. Although it has only been found between December and February, and despite the above disparity, there is insufficient information to rule out breeding in the Nakhon Sawan area (6,11). In conclusion, it is unclear whether the species is, or was, a migrant at all.

As recent searches around Bung Boraphet have been unsuccessful, let us assume it is a migrant. If it travelled across Thailand, where did it come from? The riverine nesting grounds might possibly lie along one of the four major watercourses (the Ping, Wang, Yom and Nan) which drain northern Thailand, either in the immediate vicinity of Nakhon Sawan or to the north (5,6). If it came from further afield, perhaps these putative breeding grounds lie on one of the other major river systems of South-East Asia, such as the Mekong in China, Laos or Cambodia, or the Salween and Irrawaddy in Myanmar (5,6). Evidence that the species breeds, or has ever occurred, in China is scant, although a painting by a Chinese artist held in the Sun Fung Art House of Hong Kong appears to depict the species (15). This tentative clue has failed to lead to any further information, and in any case the subject of the painting is more likely to be an Oriental Pratincole Glareola maldivarum (16).

A survey of the Nan, Yom and Wang rivers in northern Thailand was carried out in May 1969, but was not comprehensive and relied chiefly on interviewing villagers, none of whom seemed to know the bird (2). Rivers near the Chinese border of Laos were searched in April 1996, local people being shown illustrations of the species, but without success (W. Robichaud verbally 1997). Very few other surveys have looked for it outside Thailand and there is still scope for research in remote regions where a population might survive.

Throughout its possible range there is a catalogue of pressures potentially imposed on the species (5,6). Man has drastically altered the lowlands of central and northern Thailand: huge areas are now deforested, agriculture has intensified, pesticide use is ubiquitous and urban environments have spread extensively (5,6). In addition, all major lowland rivers and their banks suffer a high level of disturbance by fishermen, hunters, vegetable growers and sand-dredgers (5,6). Whole communities of nesting riverine birds have vanished from large segments of their ranges in South-East Asia owing to habitat destruction, human persecution and intense disturbance of most navigable waterways (5,17,18). Local people routinely trap or shoot birds for food and for sale in local markets (5,6). Even at Bung Boraphet Non-Hunting Area (established in 19793) the trapping of birds has continued, at some level, up to the present (5,6). If the species preferentially forages over forest, its numbers could already have declined to a perilously low level at the time of its discovery because of deforestation and the intensification of agriculture in river valleys (5,6).

These threats are based on the ecological traits inferred by its suspected taxonomic affinities. It should be borne in mind that riverine nesting habits and preferences for forest are only an assumption, and that it might conceivably utilise some entirely different habitat. Even the name river-martin is perhaps a complete misnomer, as the species has never been seen on a river and is no longer considered congeneric with the African River-Martin (7). Interestingly, the most recent scrutiny of specimens suggested that it was perhaps nocturnal, or at least highly crepuscular, based principally on its unusually large eyes (19). This raises the possibility that it is normally a cave dweller or a hole-rooster in trees or rock, emerging to feed in twilight or darkness, and this opens up new avenues of exploration. There are, for example, limestone caves not far from Bung Boraphet, and many more in Laos and southern China.

While there is only a faint chance that this, one of the most elusive species in the world (15) still survives, it bears the extraordinary distinction of being highly unusual in appearance yet overlooked by naturalists in a well-worked country until the late 1960s. As it is thus either extremely rare or inexplicably cryptic, it is not yet time to give up hope for the swollen-eyed bird. Its possible range should be revisited with a broader outlook. The prize, to any successful searcher, is considerable: solving one of the most puzzling mysteries of Asian ornithology.

References

  1. Thonglongya, Kitti (1968) A new martin of the genus Pseudochelidon from Thailand. Thai National Scientific Papers, Fauna Series no. 1. Bangkok: Applied Scientific Research Corporation of Thailand.
  2. Thonglongya, Kitti (1969) Report on an expedition in northern Thailand to look for breeding sites of Pseudochelidon sirintarae (21 May to 27 June). Bangkok: Applied Scientific Research Corporation of Thailand
  3. Sophason and Dobias (1984) The fate of the Princess Bird, or White-eyed River Martin (Pseudochelidon sirintarae). Nat. Hist. Bull. Siam Soc. 32(1): 1-10.
  4. Turner and Rose (1989) Swallows and martins of the world. Bromley, UK: Christopher Helm.
  5. Round, P. D. (1990) Bird of the month: White-eyed River-Martin. Bangkok Bird Club Bulletin 7(1): 10-11.
  6. BirdLife International (in press) Threatened birds of Asia.
  7. Brooke, R. K. (1972) Generic limits in old world Apodidae and Hirundinidae. Bull. Brit. Orn. Cl. 93: 53-57.
  8. Zusi, R. L. (1978) Remarks on the generic allocation of Pseudochelidon sirintarae. Bull. Brit. Orn. Cl. 98(1): 13-15.
  9. Mayr, E. and Amadon, D. (1951) A classification of recent birds. Amer. Mus. Novit. 1496: 1-42.
  10. King and Kanwanich (1978) First wild sighting of the White-eyed River-Martin, Pseudochelidon sirintarae. Biol. Cons. 13: 183-185.
  11. D. Ogle in litt. (1986).
  12. Anon. (1981) A search for the White-eyed River Martin, Pseudochelidon sirintarae, at Bung Boraphet, central Thailand. Bangkok: Association for the conservation of Wildlife of Thailand. Unpublished report.
  13. D. Ogle in litt. (19871988).
  14. Keith. S., Urban, E. K. and Fry, C. H. (1992) The Birds of Africa, volume 4. London: Academic Press.
  15. Dickinson, E. (1986) Does the White-eyed River-Martin Pseudochelidon sirintarae breed in China? Forktail 2: 95-96.
  16. Parkes, K. C. (1987) Letter: was the Chinese White-eyed River-Martin an Oriental Pratincole? Forktail 3: 68-69.
  17. Scott, D. A. (ed.) (1989) A Directory of Asian Wetlands. IUCN, Gland, Switzerland and Cambridge, UK.
  18. Duckworth, J. W., Salter, R. E. and Khounboline, K. (compilers) (1999) Wildlife in Lao PDR: 1999 Status Report. Vientiane: IUCN-The World Conservation Union/Wildlife Conservation Society/Centre for Protected Areas and Watershed Management.
  19. P. M. Rasmussen in litt. (2000).
  20. Ogle, D. (1986) The status and seasonality of birds in Nakhon Sawan Province, Thailand. Nat. Hist. Bull. Siam Soc. 34: 115-143.

Acknowledgements
This article is based on information to be published in the forthcoming Threatened Birds of Asia, a project sponsored by the Japanese governments Environment Agency and conducted through the BirdLife Asia Council working through the Wild Bird Society of Japan.


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