Little known Oriental Bird: White-eyed River-Martin: 1by Joe Tobias, from OBC Bulletin 31, June 2000. In January 1968, during the course of ringing activities at a wetland site in south-central Thailand, fieldworkers discovered a strange swallow amongst large numbers of migrant hirundines. It proved to be a new species and was christened the White-eyed River-Martin Pseudochelidon sirintarae by Kitti Thonglongya who dedicated this spectacular and beautiful bird to Princess Sirindhorn Thepratanasuda. Over the next three years several more specimens were collected at the same site, but apart from these, and a fleeting observation in 1978, this remarkable bird has effectively vanished. An avian enigma, it has come to epitomise the mythical allure of rarity to the birdwatcher, and for three decades it has symbolised the Asian mystery of the ornithological world. As such it has appeared in logo form in the pages of this journal as the archetypal little-known bird. The time has come to compile our knowledge of the species and to present it afresh in the hope that it might lead to a dramatic rediscovery. To begin with, we need to retrace the events of January and February 1968 and glean what we can from the available facts. The site of discovery is first misleadingly given as a big marsh on the Chao Praya River (1). The type-locality is then specified as Bung (= Nong = Lake) Boraphet, Amphoe Muang, Nakhon Sawan Province, central Thailand (1), and from its subsequent description as a shallow, marshy, reed-filled lake of 25,000 hectares it seems clear that this is the big marsh originally mentioned (a point confirmed by Thonglongya (2)). Rediscovery efforts in 1980-1981 were apparently concentrated on an island where all of Kitti's river martins had been captured (3), suggesting that, at one time, confidence was high that a very precise origin was known.
This no longer appears to be the case. The first White-eyed River-Martins were reportedly caught while night-trapping roosting swallows (Hirundo rustica, H. daurica, Riparia riparia), wagtails and warblers by casting a fishing net over a reedbed (1) a method repeated by subsequent authors (3,4,5). However, according to a local technician who worked with the original field team, the birds were neither seen in the field nor trapped by any of the team members, but rather were brought in to the teams hotel in nearby Nakhon Sawan by villagers following a broadcast appeal for live wild birds for ringing purposes (6). It seems likely, therefore, that the precise site of collection is impossible to determine, but that it is certainly in the region of Bung Boraphet, and most likely at the lake itself. Whatever their exact origins, nine specimens were initially collected: one each on 28 and 29 January (although the label on specimen 53-1218 actually states 27 January 1968 (6)) and seven on 10 February 1968 (1). From analysis of the resultant skins its closest ally was deemed to be the African River-Martin Pseudochelidon eurystomina (1). Initially described as congeneric (1), the African species and the Asian species differ markedly in the size of their bills and eyes, suggesting that they have very different feeding ecologies, sirintarae probably being able to take much larger prey and perhaps in different microhabitats (7). The gape of sirintarae is swollen and hardened, unlike the softer, fleshier, much less prominent gape of eurystomina(1,19). The feet and claws of sirintarae are unusually large and robust for an aerial feeder (1) and the two species also have different toe proportions, which might suggest dissimilar nesting habits (19). These differences are sufficiently pronounced in the view of some taxonomists to permit the allocation of its own genus, Eurochelidon (7), although other authors support the retention of both species in Pseudochelidon, arguing that they mirror patterns in other congeneric hirundines (8). Whether treated as one genus, or two, the syringeal structures of the two river-martins are divergent enough from those of the Hirundininae to confirm subfamily distinction from the true swallows, and apparently enough to suggest that they might belong in a separate family (1,9). Shortly after these first specimens, a tenth bird was caught in November 1968 (2) and brought alive to Bangkok where it was photographed in December 1968 (3). Furthermore, at least two birds (one pair) reached but soon afterwards died in Dusit Zoo in Bangkok in early 1971 (3). The only widely reported field observation was of six individuals flying low over Bung Boraphet towards dusk on 3 February 1978 (10). In addition, four probable immature White-eyed River-Martins were reportedly observed perched in trees on Temple Island in Bung Boraphet in January 1980 (3,5), and one was reputedly trapped by local people in 1986 (11). Both these records remain unconfirmed. Several subsequent searches have tried to locate the species around the site. For example, eleven amateur birding groups surveyed the lake unsuccessfully during 1979 (3). Investigations were carried out between December 1980 to March 1981 by a team from the Association for the Conservation of Wildlife but, despite netting many roosting Barn Swallows in reedbeds, they failed to reveal any river-martins (12). In 1988 another concerted effort to relocate the species was undertaken at Bung Boraphet, ending with failure as the swallow roosts were highly disturbed and mobile (13). The real number of White-eyed River-Martins trapped in the 1960s and 1970s may have been much higher than these figures suggest. In the wave of public and media interest following the sensational discovery of the species, trappers are rumoured to have caught around 120 individuals and sold them to the director of the Nakhon Sawan Fisheries Station (3,5). Moreover, local markets were reported to have had several other specimens in January-February of succeeding years (10). Having been found on Thai soil and decorated with the name of Thai royalty, there was a significant local demand for specimens or caged examples of the species, for zoos, presentation to dignitaries or as curios for the affluent. What has become of the White-eyed River-Martin? Did this harvest of hirundines extinguish it entirely? Were these last known individuals merely the doomed remnants of a population displaced by disturbance from a specialised breeding habitat? (5) Perhaps. It is quite conceivably extinct, and if it still survives its population seems likely to be tiny. The original series of specimens taken in early 1968 were outnumbered by hordes of trapped Barn Swallows by a ratio of 9:6,000 (1). In spite of this exceptional rarity, it was thought that the species might be regular at Bung Boraphet since the local bird-catchers had a name for it, nok ta phong, the swollen-eyed bird (1). Unfortunately, there has been a drastic decline in the Bung Boraphet swallow population from 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 (3). However, an estimated 100,000 swallows were present at a roost near Chotiravi, near Bung Boraphet, in August 1986 (11) and there were 30,000 at Bung Boraphet in May 1988 (11). Nevertheless, a dealer working the large Chotiravi roost claimed never to have encountered the species (11). The general feeling is that an absence of sightings since early 1980, despite numerous observational efforts, cast ominous doubts over the survival of the White-eyed River-Martin (3). Unfortunately, the habits of swallows around the lake appear to have altered recently, with very few birds roosting in the reedbeds until late winter (13). Much of the population now roosts in sugar cane plantations, moving back to the reedbeds after the cane has been harvested (13). The roosts also form well after dark, whereas they once gathered before dusk (13). These changes are probably the result of prolonged disturbance by trappers (11). In any case, the swallow roosts are more mobile and difficult to locate, factors that have further obstructed the rediscovery of the White-eyed River-Martin. The reduction in Barn Swallow populations in the Bung Boraphet area is difficult to explain but intensive trapping activities for the purpose of selling birds as food in local markets must have played a major role, as must the annual destruction of roosting sites to make way for lotus cultivation (3). Huge areas of reedbed in areas frequented by roosting swallows were being burnt in February 1986 (11). The hunting of hirundines without a licence has been illegal since 1972, although this legislation is rarely enforced (3). Relations between conservationists and bird trappers at Bung Boraphet are occasionally fraught, to the extent that a reserve ranger was killed when trying to apprehend poachers at roosts in 1987 (13). |
