Asian Openbill Anastomus oscitans Scientific name definitions

68–81 cm. Fairly large, mostly white stork with diagnostic bill showing space between mandibles when closed. Adult has greyish-white plumage with black flight feathers and tail. Forked tail black , but usually hidden by long undertail-coverts. Broad, horn-coloured bill. Immature smoky brownish grey  with darker mantle, bill straightish  .

India (N plains from Gujarat E to Assam Valley, and in E & S Peninsula), S Nepal and Sri Lanka to Thailand and Indochina; has recently colonized SW China (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ). Non-breeding in most of peninsular India, Bangladesh and E Pakistan (NE Punjab, S Sind) (2 Rasmussen, P. C., and J. C. Anderton (2012). Birds of South Asia. The Ripley Guide. Volumes 1 and 2. Second edition. National Museum of Natural History, Smithsonian Institution, Michigan State University and Lynx Edicions, Washington, DC, Michigan, MI, and Barcelona, Spain. Close ).

A variety of wetlands , including lakes, jheels, canals, rivers, marshes and occasionally mudflats; paddyfields also frequently used, even in dry season in Thailand when mud caked hard; also in newly ploughed fields. May nest near humans. Recorded to 3840 m in SW China (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ).

Mostly local movements occur after breeding, depending on water conditions. There is probably also some juvenile dispersal. Thai birds have been recovered in Cambodia, N Thailand and Bangladesh, and undoubtedly account for many sight records in Myanmar. Most of Thai population migrates W to deltas of Ganges and Brahmaputra during wet season, although some are sedentary. Some birds presumably originating from Tonle Sap, Cambodia, move to the Mekong Delta outside breeding season: gatherings of 200+ have been reported there from Boeung Prek Lapouv, Cambodia, and Tra Su, Vietnam, where there is now a breeding colony (3 Van Zalinge, R., Visal, S., Phreakdey, S. and Evans, T. (2011). The status and distribution of large waterbirds in the Tonle Sap Biosphere Reserve, 2010 update. Wildlife Conservation Society Cambodia Program, Phnom Penh. Close ). Birds from NW India may also move E towards Bangladesh, with several records of birds migrating on dark nights crashing into lighthouses in C & S India. Vagrant to Malaysia and Laos (4 Chye, L. K. and Yian, L. S. (2009). First record of Asian Openbill Anastomus oscitans in Malaysia. BirdingASIA. 11: 103. Close , 5 Evans, T. D., H. C. Towll, R. J. Timmins, R. M. Thewlis, A. J. Stones, W. G. Robichaud, and J. Barzen (2000). Ornithological records from the lowlands of southern Laos during December 1995–September 1996, including areas on the Thai and Cambodian borders. Forktail 16:29–52. Close ). In Peninsular Malaysia, an influx in Jan 2013 involved some 6000–7000 birds (6 Bakewell, D. (2013). Conservation plan for the Asian Openbill in Peninsular Malaysia. Suara Enggang. 21(3): 28–40. Close ). 

Almost entirely apple snailsBird with snail (Pila); occasionally other small aquatic animals, such as frogs, crabs and large insects. In SW China, observed taking large snails and freshwater mussels, incluing Chinese mystery snail (Cipangopaludina chinensis), river snail (Bellamya aeruginosa) and Chinese pond mussel (Anodonta woodiana) (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ). Specialized bill and technique enables species to exploit abundant source of food, which is inaccessible to most other potential predators. Snails extracted by inserting bill, virtually without damage to shells. Will feed in close association with other large wading birds, e.g. Cattle Egret (Bubulcus ibis), Little Egret (Egretta garzetta), Great White Egret (Ardea alba) and Grey Heron (A. cinerea) (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ).

Largely silent away from the breeding colonies. Around nest, utters hollow honks, often in slightly descending and accelerating series “hurh..hurh..hurh-hurh-huh-huh”, and hissing sounds. Young beg for food by calling incessantly “wek-wek-wek-wek...wek-wek-wek-wek...”.

Mostly Jul–Sept in N India, Nov–Mar in S India and Sri Lanka, starting at onset of rains; in dry season in Thailand, with most laying in Jan. Colonial tree nester , sometimes in mixed colonies with herons, cormorants and Mycteria leucocephala; smallish, unelaborated stick nest with central depression lined with leaves; nests often very close together, with 100s spread over a few large trees, but may also nest in smaller trees, e.g. Avicennia, or even bamboo. Normally four eggs (2–5); incubation 27–30 days; chicks have pale fawn-coloured down and normal bill; eggs and young may be taken by monitor lizards (Varanus), crows or raptors; fledging reportedly 35–36 days, probably averages more. Oldest captive bird only seven years old.

Not globally threatened (Least Concern). The commonest Asian stork, although it is under threat in some regions and has a much more discontinuous distribution than formerly; most recent census (2007) of population recorded more than 258,000 individuals. Still locally common at scattered sites throughout India: e.g., 5181 at Keoladeo (Bharatpur), Rajasthan, in 1981 and > 10,000 in the Indian Sundarbans in 1977. A midwinter census in Jan 1991 found 9683 birds in India (5380 in Orissa, 2316 in Tamil Nadu), 804 in Sri Lanka, 1286 in Myanmar and 200 in Thailand; some populations were clearly underestimated then. No evidence of regular breeding in Pakistan since early 1930s, and now considered rare visitor to Sind (where formerly common) and the Punjab. Has also largely ceased to breed in Bangladesh due to hunting pressure, disturbance and habitat destruction, though non-breeding migrants occur. Population in Thailand declined during 20th century until just one colony remained, at Wat Phai Lom (Phai Lom temple) near Bangkok. This large, protected colony held 8000–14,000 pairs at its peak in mid 1980s, which damaged the nesting trees (see Family introduction). Several smaller colonies have appeared elsewhere in C & N Thailand in more recent years, as far N as L Chiang Saen (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ). Only three recent records from peninsular Thailand prior to 2004 but since then 570 counted at Chumphon on 22 Jan 2008 and 20 were at Laguna, Phuket, on 16 Dec 2008. The apparent spread southwards (as far as Singapore) is thought to be associated with the spread of the alien rice crop pest, golden apple snail (Pomacea canaliculata), which is a prey species of the stork (7 Bakewell, D. (2010). The work of the Malaysian Nature Society-Bird Conservation Council Records Committee (MNS-BCC RC) and updates to the status of birds in Malaysia. BirdingASIA 13:22–29. Close ). In N of range, the species has recently colonized SW China, where first recorded in Oct 2006, in Yunnan, but has since spread across much of province, as well as E over much of Guizhou and to one locality in Guangxi, ironically perhaps facilitated by habitat degradation (1 Liu, Q, Buzzard, P. and Luo, X. (2015). Rapid range expansion of Asian Openbill Anastomus oscitans in China. Forktail. 31: 118–120. Close ). Another large and protected colony is at Prek Toal, Tonle Sap, Cambodia: a partial survey in 2010 found 13,845 pairs (3 Van Zalinge, R., Visal, S., Phreakdey, S. and Evans, T. (2011). The status and distribution of large waterbirds in the Tonle Sap Biosphere Reserve, 2010 update. Wildlife Conservation Society Cambodia Program, Phnom Penh. Close ). Observations have become more widespread in Vietnam in recent years, following a long decline, and a colony of some 100s of pairs is reported from Tra Su in the Mekong Delta. The species has long suffered from hunting and trapping in some countries, as well as habitat destruction. It may be affected by accumulating pesticides from snails and it has been proposed as a potential indicator species of pollution levels. Protection of its often large colonies and nearby feeding grounds is relatively easy and effective and has clearly been very successful locally.