The Black Headed Ibis (Threskiornins melanocephalus), also known as
the Oriental white ibis, is a large wader found over a large range of
South-eastern Asia. It is a large Ciconiiform (order comprising
storklike birds) with adults measuring 65-70cm.
It is the only native ibis species in its range that has an overall
white plumage with a black neck and head. The down-curved beak and legs
are also black.
Introduction
The black headed ibis is a medium, nomadic, wading waterbird, frequently
found in association with other Ciconiiforms or pelicaniiforms in
shallow waters. They are gregarious feeders, with a diet comprising
grass, plant material, amphibians, crustaceans and water snakes.
The black-headed ibis is very versatile being able to use a large
variety of natural and man-made habitats. These include freshwater and
salt-water marshes, lakes and ponds, as also rice fields, freshly
ploughed crop fields, irrigation canals, riversides, reservoirs, urban
lakes, open sewage gutters, grazing lots, and garbage dumping sites.
Ibis alter use of varied preferred foraging habitats by season in
agricultural landscapes such as in south-western Uttar Pradesh in India.
In summer, they largely use and prefer natural marshes and fallow
fields, but in the monsoon, spread out more evenly to also use a variety
of agricultural fields.
Like many storks and spoonbills, blackheaded ibises lack a true
voice-producing mechaninsm and are mostly silent, except for
ventriloquistic grunts uttered by pairs at the nest.
Nesting
Ibises nest and roost in coloies called heronries or egretries, in association with other waterbirds, in and around wetlands. They are monsoon breeders, probably due to the abundance of resources in wetlands during this time.
It is a colonial breeder, nesting on moderate to tall-sized trees such as Prosopis, Acacia and various species of Ficus which stand in or near water. The main breeding season of black headed ibises is from June to August in Northern India, and From November to February in SOuthern India, just in time for the monsoons. The breeding activities of the ibis is heavily influenced by the rain, and immediate rainfall after the normal rainy season have been found to induce vigourous reproductive activities in this species, often eading to a decrease in breeding efficiency.
Selection of nesting sites
The white ibis does not have a very strong site-fidelity. What then, would influence the choices of these birds while choosing a nesting site?
Vegetative characteristics: It has been found that even though the majority of breeding sites change each season, nests are usually located on trees with a dense and rich canopy cover that provides and ideal nesting platform. The thick canopy also prevents the chicks from falling directly to the ground. The dense canopy also protects chicks from direct thermal stress, and minimises the requirement of wing shading by the parents, thus reducing the energy cost.
Familiarity bias: Ibises have often been found to reuse old nesting sites, probably because of the benefits in foraging and predation avoidance brough about by familiarity with a site.
Ibises have also often been found to displace majority of their nesting colonies every breeding season to achieve maximum breeding success.
Extra-pair copulation most often occurs when the male is absent from the nest for the collection of nest material (Frederick, 1987b; Aguilera and Alvarez, 1989). Therefore, the time and energy saved by reusing a nest could be used by the male for other important reproductive activities such as protection of the nest and mate guarding.
Breeding Plumage
Tails of adults bear light grey ornamental feathers that turn jet black during the breeding season. During the breeding season, bare patches under the wing turn blood-red. The head of some breeding adults gain a blueish tinge, or very rarely have a pink or bright red patch behind the neck. Some breeding adults also develop tufts of white feathers behind the neck, and rarely also get a yellowish colouration on the breast and back. Sexes are identical but juveniles are identifiable from adults in having greyish feathering on the neck and speckled brown-grey feathering on the wings and back.
References:
