Of all the large waterbirds in Indochina, the species that has undergone the most dramatic decline is White-shouldered Ibis Pseudibis davisoni. In the first half of the twentieth century, the species was described as "common" in parts of Cambodia, and also occurred in Thailand and Vietnam. The species is now believed extinct in Thailand and known from only two sites in Vietnam, neither of which is believed to support a viable population. In Cambodia, where recent years have seen a resurgence of fieldwork following decades of instability, there have been only a few, scattered records of this species. The lack of recent records contrasts markedly with the discovery of significant populations of Giant Ibis, a species previously considered rarer than its smaller relative.

In May 2002, a team from BirdLife, WCS, DoF, NCDP and Virachey National Park spent five days in western Siem Pang district, Stung Treng province, northern Cambodia. This site was selected as the focus of a survey for White-shouldered Ibis because two captive juvenile birds, reportedly taken from a nest in the west of the district, were seen during a previous survey. In addition, the site is bordered to the north by Xe Pian Protected Area in Laos, the only site in that country with confirmed recent records of White-shouldered Ibis.

On the first day of the survey, one member of the team made a reconnaissance trip to a seasonal pool, in an area of rice fields, close to Siem Pang town, where he saw two White-shouldered Ibis feeding among domestic buffalo and cattle. The following day, the team waited at this pool, in an attempt to photograph the birds. While the team was waiting, a group of local people passed through the area. When interviewed, they reported seeing a flock of White-shouldered Ibis earlier that morning, at another pool, further from the town. On the way to check out these reports, the team flushed a group of four White-shouldered Ibis from a rain-filled ox-cart track. Later on that same day, a further two birds were seen at the pool mentioned by the local people. On the following day, a single bird was seen and photographed at this pool.

Four records, of a total of 10 birds, over only three days are quite unprecedented. These records were particularly surprising given that they were all within 8 km of Siem Pang town, and at wetlands with moderate to high levels of human disturbance. However, the records lend credence to reports by local people that White-shouldered Ibises visit their rice fields at the start of the dry season, in flocks of 10 to 15, in the company of Woolly-necked Storks Ciconia episcopus and other large waterbirds.

To date, western Siem Pang district is the only site in Indochina known to support a significant population of White-shouldered Ibis, a critically endangered species. In addition, the site supports a number of other species of conservation concern, such as Giant Ibis Pseudibis gigantea, Red-headed Vulture Sarcogyps calvus, Lesser Adjutant Leptoptilos javanicus and a suite of riverine species, including Great Thick-knee Esacus recurvirostris, River Tern Sterna aurantia and Mekong Wagtail Motacilla samveasnae. Furthermore, local people report that the site supports a significant population of Eld's Deer Cervus eldii. The site should, therefore, be considered a priority for conservation action.