White-bellied heron (Ardea insignis)
|Also known as:||imperial heron|
|Size||Length: 127 cm (2)|
The white-bellied heron is classified as Critically Endangered (CR) on the IUCN Red List (1).
Also known as the imperial heron, the white-bellied heron (Ardea insignis) is the second largest species of heron in the world, exceeded in size only by the Goliath heron (Ardea goliath). This large, long-necked species is named for its white underbelly and wing linings (3).
The male white-bellied heron is very similar in appearance to the female, with a blackish head topped with a pale plume of feathers, and a brownish-grey body with grey wings, legs and feet. The chick differs from the adult in being white with a yellow underbelly, which lightens as the heron matures. The most outstanding feature of the white-bellied heron is its massive pointed bill, which measures about 15 to 18 centimetres in length (3).
The white-bellied heron has a loud, deep ‘ock ock ock ock urrrrrr’ call (2).
The white-bellied heron is resident in Southeast Asia, from the foothills of the Himalayas in Bhutan, through north-eastern India, into the hilly regions of Bangladesh and south into Myanmar. It may also potentially occur in Southeast Tibet, China. Historically, the range of the white-bellied heron also spread into west and central Myanmar as well as Nepal, but it is now believed to be extinct in Nepal (2).
The white-bellied heron inhabits rivers with sand or gravel bars, usually with adjacent broadleaved forest, from lowlands up to elevations of around 1,500 metres (2). The white-bellied heron can also be found around inland swamp forests and occasionally in grasslands at the base of mountain ranges. In contrast to other members of its genus, it prefers forested and sheltered areas to open wetland (3).
The specific diet of the white-bellied heron is not well known, but it is thought to generally consist of crustaceans, insects and fish, which it catches in and around fast-flowing rivers. The white-bellied heron tends to feed alone; pairs or family groups may feed in the same area, but individuals will hunt solitarily. Feeding takes place mainly during daylight hours with the heron flying to its chosen hunting site and remaining there all day, spearing food with its bill, before returning to roost in the evening (3).
The white-bellied heron breeds and nests in trees, between March and June. In Bhutan it has been found to prefer nesting sites near rivers where there are forests of Chir pine (Pinus roxburghii) in which to build its large nests (2). A small clutch of greenish-blue eggs is laid and incubated alternately by the male and female. Once hatched, the chicks are fed on regurgitated fish and leave the nest at between two and three months old (3).
Although primarily a solitary bird with a large territory, during the winter months the white-bellied heron may fly up to 30 kilometres to join other members of the species in small family groups or flocks of unrelated individuals (2) (3). With a large territory and its solitary habit, the population density of the white-bellied heron has never been as high as some of its more common relatives (3).
For over a century the white-bellied heron has been at risk due to deforestation because its preferred habitat is mature forest (3). It is also under threat from the fragmentation and degradation of its wetland habitats through pollution, over-exploitation of resources and the rapid growth of aquatic vegetation due to leaching of artificial fertilisers (2). In addition, the white-bellied heron is vulnerable to disturbance and habitat degradation as a result of agricultural expansion, human settlements and poaching (2), as well as overfishing (3).
There is high nestling mortality in this species due to predation and the risks associated with forest fires (4). As the white-bellied heron frequents fast-flowing rivers, it is also extremely susceptible to disturbance from transport routes, and from hydroelectric-power development, especially in Bhutan (2).
The white-bellied heron population is extremely small, at fewer than 250 mature individuals, and is rapidly declining, putting this species at severe risk of extinction (2).
The Royal Society for the Protection of Nature (RSPN) began a conservation programme in Bhutan in 2003 to increase the rapidly-declining population of the white-bellied heron (2) (4). In May 2011, the first white-bellied heron chick to be bred in captivity hatched in Bhutan as a result of this project (4). The Government of Bhutan has recognised the riverbed area of Punakha-Wangdue as an important white-bellied heron feeding site, and has designated it as a protected habitat to preserve the species (2).
There are records of sightings of the white-bellied heron in several protected regions of north-eastern India, including the Namdapha Tiger Reserve, where it is believed to breed (2), and the Kaziranga National Park (2) (5). Improved conservation in these areas is planned, including the creation of buffer zones around the borders of the reserve (2).
Little is known about the exact status of the white-bellied heron, so an extensive survey into the extent of its population and range has been proposed. Satellite tagging of individuals has been suggested in order to understand more about its range and migratory patterns, as has conservation awareness education to reduce the human impact on the white-bellied heron and its habitat (2).
More information on the white-bellied heron and heron conservation:
BirdLife International - White-bellied heron:
Find out more about conservation n Bhutan:
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- Crustaceans: diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Incubate: to keep eggs warm so that development is possible.
- Territory: an area occupied and defended by an animal, a pair of animals or a group.
IUCN Red List (November, 2011)
BirdLife International (November, 2011)
- Kushlan, J. and Hancock, J. (2005) Herons. Oxford University Press, Oxford.
WWF Bhutan (November, 2011)
- Barua, M. and Sharma, P. (1999) Birds of Kaziranga National Park. Forktail, 15: 47-60.