Asian Openbill (Anastomus oscitans)

Asian Openbill

[order] CICONIIFORMES | [family] Ciconiidae | [latin] Anastomus oscitans | [authority] Boddaert, 1783 | [UK] Asian Openbill | [FR] Bec-ouvert indien | [DE] Silber-Klaffschnabel | [ES] Ciguena de Pico Abierto Hindu | [NL] Indische Gaper


Genus Species subspecies Region Range
Anastomus oscitans OR India, Southeast Asia


The openbill storks or openbills are two species of stork (family Ciconiidae) in the genus Anastomus. They are large wading birds characterized by large bills, the mandibles of which do not meet except at the tip. This feature develops only in the adults. The two species of openbill storks are the Asian Openbill (A. oscitans), a resident breeder in tropical southern Asia from India and Sri Lanka east to Southeast Asia. Next the African Openbill (A. lamelligerus,) a resident breeder in Africa and Madagascar.

Physical charateristics

It is a small stork with conspicuous gap in its bill. Adult has white plumage in breeding season, and pale grey for rest of the year. Scapulars, flight feathers and tail are black.

Head is white or grey. The open bill is formed by a hollow in the lower mandible. Both mandibles meet at tip. Large, strong bill is pale pinkish-grey. Eyes are dark brown. Lores are greyish to pinkish. Long legs and feet are pinkish to red. Both sexes are similar.

Juvenile have brown tinge, instead white or pale grey. Bill is dark grey with lower mandible almost straight. Gap forms later.

Listen to the sound of Asian Openbill

[audio: Openbill.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 145 cm wingspan max.: 150 cm
size min.: 76 cm size max.: 81 cm
incubation min.: 27 days incubation max.: 30 days
fledging min.: 35 days fledging max.: 36 days
broods: 1   eggs min.: 1  
      eggs max.: 4  


Oriental Region : India. Asian Openbill is resident in tropical southern Asia, from India and Sri Lanka, east to south-eastern Asia.
, Southeast Asia


This stork feeds in rice-fields and marshes in freshwater. It breeds near inland wetlands. It lives in shallow marshes and flooded areas.


It nests in colonies, with numerous nests in the same tree, up to 40 and more. Long courtship displays occur at the beginning of breeding season.
In threat displays, Asian Openbill has open wings and neck outstretched. Usually, rivals threaten each other, but rarely fight. Asian Openbill nests in colonies with other species, such as Herons. Nest is located in trees or bamboos. It is made with sticks, and interior is lined with green leaves. Female usually lays 2 to 4 white eggs. Incubation lasts about 27 to 30 days, and young fledge at 35 to 36 days after hatching. Young birds are greyish, with dark bill. They stand and wait for adults. Parents approach the nest cautiously, and regurgitate the food. Adults shade their young in the nest, to protect them from sun. One of the parents stands in the nest with open wings above the chicks.

Feeding habits

Asian Openbill feeds mainly on molluscs, and particularly freshwater snails, Apple Snails, (genus ‘Pila’ – Ampullariidae), living in rice-fields and swamps. Prey is located by touch and sight. The gap in the bill allows good grasp of the snail’s shell. Asian Openbill walks slowly in shallow water, searching for prey. It extracts snail from the shell, with pointed lower mandible.

Video Asian Openbill


copyright: Josep del Hoyo


This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
It is the most common Asian stork, and populations are not threatened.
Most important colonies are protected, as those of Wat Pai Lom and San Lon, in Thailand.
Asian Openbill status Least Concern


This species populations are resident in their range. Some groups may move after breeding season, but most of them are sedentary. Breeding season depends on the location. Northern populations breed from July to September, and southern birds breed from November to March

Distribution map

Asian Openbill distribution range map

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