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Asian Openbill
Anastomus oscitans

Ciconiiforme Order – Ciconiidae Family

Length : 76 à 81 cm
Wingspan : 147 à 149 cm

Asian Openbill is a small stork with conspicuous gap in its bill, allowing the bird to catch its preferred food, the freshwater snails.

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.

Asian Openbill 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.    

Fr: Bec ouvert Indien
All :  Silberklaffschnabel
Esp : Picotenaza Asiático
Ital : Anastomo asiatico
Nd : Indische Gaper
Russe : Аист-разиня индийский

Photographs by Didier Buysse
His website : Vision d’Oiseaux

Text by Nicole Bouglouan


HANDBOOK OF THE BIRDS OF THE WORLD vol 1 by Josep del Hoyo-Andrew Elliot-Jordi Sargatal - Lynx Edicions - ISBN: 8487334105

LES OISEAUX DE THAILANDE par Roland Eve et Anne-Marie Guigue - Times Editions - ISBN: 9812042008

Avibase (Lepage Denis)

SORA Searchable Ornithological Research Archive (Blair O. Wolf)

Wikipedia (Wikipedia, The Free Encyclopedia)


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Asian Openbills are very noisy while flying in flocks. We can hear a continual hubbub, as the gabbling of hundreds of ducks. Call is a mournful “hoo-hoo”.

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

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

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.

Asian Openbill 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. They are very social birds. 

Asian Openbill 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 uses warm airstreams for rising in the air, and flies high in the sky. Then, it glides to destination.
Landing is spectacular. Asian Openbill drops from the air as a parachute, with dangling legs, and lands.

Asian Openbill nests in colonies with other species, such as Ardeidae. 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 semi-open wings above the chicks. 
Asian Openbill is usually monogamous, but polygamy exists. In this case, all members of polygamous nest raise the young, and brood success is more important than in monogamous nests.

Asian Openbill feeds mainly on Apple Snails, but it also consumes frogs, crabs and large insects, and other small aquatic animals.