Pseudibis davisoni

The white-shouldered ibis is a relatively large ibis species in the Threskiornithidae family. It is native to small regions of Southeast Asia, and is considered to be one of the most threatened bird species of this part of the continent. The white-shouldered ibis was first described by Hume (1875), who originally named the species Geronticus davisoni after his bird collector William Ruxton Davison. Based on this species’ observed similarity with the black ibis (Elliot, 1877), the two species were placed in the same genus. In the more recent past, this ibis has often been classified as a subspecies of the black ibis; but is currently recognised as a separate species. The adult of this large ibis stands 60–85 cm tall, with males being slightly larger and having slightly longer bills than females. Its only available biometrics are measurements from a single unsexed specimen originating from the 19th century, which include a wing length of 419mm, culmen length of 197mm, tarsus length of 83mm and tail length of 229mm. The plumage is brownish-black, with glossy blue-black wings and tail, and a bare slate-black head which has also been reported as blue or white. A conspicuous neck collar comprising a bluish-white band of bare skin which is broader at the back and narrower at the front extends from the chin around to the nape at the base of the skull. The pale blue is most easily detectable at close range, although this collar has been noted to be completely white in some individuals. The legs are dull red, the iris is orange-red, and the large de-curved bill is yellowish-grey. The white-shouldered ibis probably owes its name to the clear white observed on the upper part of the neck and chin in some individuals, which may appear as “white shoulders” in flight. In flight, it is also identified by its conspicuous white wing patch, which is visible only as a thin white line when the wings are closed. The white-shouldered ibis is morphologically similar to its Indian congener the black or red-naped ibis Pseudibis papillosa, but lacks the red tubercles on the nape; and is slightly larger, more robust and has a longer neck and legs. The tail also appears to be shorter and spreads downwards in contrast to straight in the black ibis. The juvenile has dull-brown plumage along with a tuft of brown feathers on the bluish-white nape, a grey-brown iris, pale yellow legs and dull white feet. Its vocalisations generally consist of loud, mournful calls that have been described as “weird and unearthly screams”. The hoarse calls of territorial individuals have been described as “errrrh” or “errrrrroh”. It also utters honking screams of “errrrh owk owk owk owk owk” and more subdued “ohhaaa ohhaaa” and “errrrrah”. It makes a loud, harsh “klioh klioh” call during copulation, resembling that of the black woodpecker. This southeast Asian ibis was once markedly more widespread than presently. The former range extended throughout Southeast Asia from Myanmar to Thailand, Malaysia, Cambodia, Laos, Vietnam and north into Yuman in China. The current population is very small and its distribution highly fragmented; being restricted to northern and eastern Cambodia, southern Vietnam, extreme southern Laos and East Kalimantan. Cambodia by far forms this species’ stronghold; with 85-95% of the global population of individuals estimated here. The largest known Cambodian white-shouldered ibis subpopulation resides in Western Siem Pang Important Bird Area (minimally 346 individuals). Other sites in Cambodia that hold considerable numbers of white-shouldered ibis include Kulen Promtep Wildlife Sanctuary, Lomphat Wildlife Sanctuary and the central section of the Mekong River. It is now functionally extinct from Thailand, Myanmar,and southern China; and very scarce in Indonesian Borneo and southern Laos (Birdlife International, 2001).Thailand was once the stronghold for this species, but no official records of its occurrence have been made here since 1937.