By Jagath Gunawardana Storks, herons, bitterns, egrets, ibises and spoonbills are all closely related, belonging to the order Ciconiformes that has three different families representing 27 species in Sri Lanka. The family Threskiornithidae has only three species in the country, comprising of two species of ibises and a single species of spoonbill. The ibises are characterised by long decurved beaks while the spoonbills have, as the name denotes, a beak that has the distended tip flattened in the shape of a spoon.

The most common member of the family in Sri Lanka is the White Ibis, which is also known as the Oriental Ibis and the Black-necked Ibis. The Sinhala names Dekethi-Koka, Sudu-Daetuduwa and Daetuduwa all refer to the decurved beak, while the other name Tatta-Koka refers to the bald head.

The White Ibis (Threskiornis melanocephalus) is about 75 cm (2 1/2 feet or 30 inches) long and has a stocky build, a long neck, long legs, a long tapering decurved blunt beak that is grooved along the sides. The nostrils are placed at the upper end of this prominent groove. The head and the neck of adults is totally devoid of feathers. In juveniles the neck and the back of the head are covered with feathers. The wings are long and broad. The short tail is often hidden by the wings when at rest. In adults, the beak, head and neck are all greish-black or bluish-black. In juveniles, the feathers on the neck are grey. All the feathers in the body are a bright white in colour. Legs and feet black. Eyes are a deep dull red or dark brown. In flight, a blood red line is seen along the length of the underwing.

A social and gregarious bird, the White Ibis is usually found as groups or flocks that may at times comprise of more than a hundred individuals. On the ground, it walks in a slow, leisurly gait, the neck downcurved in the middle and the beak painted down. Unlike the storks, it usually sits in a more lateral pasture. In flight, the neck is outstretched with the beak painted forward and the long legs trail behind. The flight is fast, straight and powerful. Once airborne, it gains height quickly with rapid, continuous wingbeats. After gaining height, the flight becomes less speedy, several continuous beats of the wings being interspersed with short glides. A flock will fly either as a line or in V-formation. In flight, the blood red lines on the underwing covers show prominently.

Food consist of small fish, molluscs, worms, crustaceans, insects and other small creatures. It employs several methods to catch prey. The mostly seen is the use of the tip of the mandibles as a forceps to pick prey off the soft mud or shallow water. If the water is deeper, the beak is imersed and the bottom probed with the mandibles slightly open. A varient of this is to walk forward slowly while probing. It will venture into deeper water while probing until the water level reaches the eye when probing the bottom. Swallowing of food is helped by several upward jerks of the head. It does not make any calls, but emits a low grunt or hisses when annoyed or startled. When disturbed on ground, it quickly takes flight to alight on a nearby branch but would fly away if frightened. A peaceful bird, it is usually seen in the company of egrets, herons, storks, spoonbills, purple coots, white-breasted waterhen and various species of waters. Occasionally one may chase another accompanied by grunts and hisses, but was never seen attacking another bird.

The breeding season commences with the North Eastern Monsoon in the Dry Zone and is from November to March. In the Wet Zone, nesting was seen by me only at the National Zoological Goldens in early 1990s when a small group that used to come to roost on some tall trees bordering the old metal quarry constructed several nests in these trees. However, White Ibises in breeding plumage have been seen in the Wet Zone from October to April. They were seen taking nesting material in the Wet Zone from December to February and occasionally in March. It is possible that breeding starts later than in the Dry Zone.

At the beginning of the breeding season both sexes develop long narrow feathers known as plumes. The plumes on the upperbreast are white while those on the inner secondaries (tertials) and scapulars are grey in colour and quite long, spreading on the back and falling down over the tail. These grey plumes are darker on some with occasional individuals sporting almost black plumes. In addition most breeding birds get a yellow colour on the breast and beak giving them a somewhat sullied look. The nest is a wide platform made up of sticks on a higher branch of a tree. They are social breeders that build many nests close to each other, and often in the company of other water birds. Mostly, it is the trees of the roosting places that are used for nesting but sometimes have to seek other places when suitable places are not available. It is common to see White Ibises sharing the same tree with little Cormarants, Indian Shags, Pond Herons, Night Herons, Grey and Purple Herons, Egrets, Spoonbills, Painted Storks, Open-bill and Grey Pelicans.

Both sexes share the burdens of nest building, incubation of eggs, tending, feeding and guarding of young. The eggs are white in colour and number 3 to 5. They take about 3 weeks to hatch. Incubating birds defend their nests by spreading the wings, painting the beaks up and lunging fast at intruders. They are harassed by hordes of House Crows in some places. But, the eggs and chicks are liable to be snatched by the White-bellied Sea Eagles which raid these mixed breeding colonies and is an enemy of all nesting waterbirds. During the hot midday adults can be seen sheding the eggs and young by spreading their wings and turning the backs towards the sun while vigorously flapping the throat to keep themselves cool. This habit of flapping the throat (called gular flapping) is common to many aquatic birds.

The White Ibis is seen in the low country Dry and Wet Zones but not in the hills. It is common and widespread in the Dry Zone but quite local in the Wet Zone. Their spread to the Wet Zone is recent G. M. Henry (1971) says it does not normally stray into the Wet Zone and it was W. W. A. Phillips (1978) who has mentioned it being found rarely in the Wet Zone. In 1987, there was a colony of 22 around the Bellanwila. Athidiya Sanctuary which had increased to 132 in 1994, and over 200 in 1996. Scattered flocks are now found in a wide swath of area from the Kelani River to Bolgoda in the Colombo and Kalutara Districts, small flocks or a few can be seen in the Gampaha District, particularly in Muturajawela. These populations are still in the increase and slowly spreading to other neighbouring areas.

However, there is no marked increase in the numbers in the Dry Zone but is seen in many newly irrigated areas as well. The White Ibis is found in the Indian sub-continent, Indo-China, Burma and Thailand to China and Japan.