Asian openbill (Anastomus oscitans)
Asian Openbill or Anastomus oscitans is a species of storks which are largely found in India, Sri Lanka and some parts of Indo China. Highly colonial, they may stay in their native range all the yearlong inhabiting wetlands migrating to specific destinations during the breeding season, generally from June to December. The Home range could be restricted to 1.5 Kms from their colonies.
They are medium sized storks about 81 cm long with a wing span ranging from 147 to 148 cms. and may weigh anywhere between 1.3 to 8.9 kg. With a pale white or gray plumage and black wings, a black forked tail and pink legs, this stork is characterized by a gap between the upper and lower mandibles, brought about by a downward curvature of the lower mandible which meets the upper mandible only at the tip. The Asian Open billed stork is carnivorous, feeding mainly on snails and small aquatic invertebrates such as mollusks, crabs and worms. Frogs, lizards insects, fishes and snakes may also from part of the diet. The space between the mandibles often helps it to hold its prey. Food is ingested whole, often the pointed lower mandibles could be used to crush hard shelled prey and extract their flesh.
Both sexes are alike with the bird being largely monogamous. Occasionally polygyny is observed. Members of polygynous nests generally share the responsibilities of nest building, incubation and caring for the young without discrimination. Males show potential nesting sites to females and often display nest material as a sexual trait. Females choose good nest builders. In monogamous nests, both parents work together to build the nest and incubate the eggs. Females lay 2 to 5 eggs per reproductive cycle and both parents incubate the eggs till hatching. The nestlings are completely dependent on the parents for about 30 to 36 days after hatching and still dependent until reaching sexual maturity at 60 days when they leave the nest and are able to breed within the same breeding season in which they were hatched.
The life span of an Asian open bill is usually 18 years in captivity.
Asian open bills are largely mute and cannot vocalise because of weak syrinx muscles. They may resort to bill clattering but rely mainly on olfactory clues. The eggs and nestlings of the Asian open bill are commonly preyed upon by crows, monitor lizards, eagles etc. for which the male and female take turns to leave the nest and forage. Nests are also made in mixed heronries with other species which is of strategic importance as it helps in keeping predation away. Members of a pair often defend their nests from intra specific intrusions.
The feces of the bird helps to fertilise the wetland plants. Meat and eggs serve for human consumption. They also control the population of snails which damage rice crops. Asian open bills may carry and transmit the H5N1 avian influenza virus.
In terms of conservation status they are largely unthreatened and of ‘Least Concern’ as per IUCN. However, several threats like wetland invasive species, destruction of wetland habitation by buffaloes, reduced food because of fishing, and poaching are putting pressers on the population.
(Based on Sanna Quarmieh, Anastomus oscitans, Asian open bill, ADW, Animal Diversity Web, University of Michigan, Museum of Zoology.
Acknowledgements-Dr. Yashpal Singh, Mrs. Neena Singh, Mr. Rajesh Bedi, Manoj Kumar Yadav