Black-necked Stork - Behaviour and Ecology

Behaviour and Ecology

This large stork has a dance-like display. A pair stalk up to each other face to face, extending their wings and fluttering the wing tips rapidly and advancing their heads until the meet. They then clatter their bills and walk away. The display lasts for a minute and may be repeated several times.

Nest building in India commences during the peak of the monsoon with most of the nests initiated during September - November, with few new nests built afterward until January. They nest in large and isolated trees on which they build a platform. The nest is large, as much as 3 to 6 feet across and made up of sticks, branches and lined with rushes, water-plants and sometimes with a mud plaster on the edges. Nests may be reused year after year. The usual clutch is four eggs which are dull white in colour and broad oval in shape, but varies from 1-5 eggs. The exact incubation period is not known but is expected to be about 30 days. The chicks hatch with white down which is replaced by a darker grey down on the neck within a week. The scapular feathers emerge first followed by the primaries. The young birds make a chack sound followed by a repeated wee-wee-wee calls. Adult birds take turns at the nest and when one returns to relieve the other, they perform a greeting display with open wings and an up and down movement of the head. Food is brought for the young chicks by the adults and regurgitated onto the nest platform. Adults stop feeding the young at the nest and begin to show aggression towards the chicks after they are about 3 or 4 months old. The young birds may stay on nearby for about a year but disperse soon. Typically 1-3 chicks fledge from successful nests, but up to four chicks fledge in years with high rainfall.

At the nest trees, which are typically tall with large boles and a wide-canopy, the birds in Bharatpur were found to compete with Indian White-backed Vultures sometimes failing to nest due to them. While many wetland birds are flushed by birds of prey, these storks are not usually intimidated and on the other hand can be quite aggressive to other large water-birds such as herons and cranes. Adults aggressively defend small depressions of deep water against egrets and herons (at Malabanjbanjdju in Kakadu National Park, Australia), and drying wetland patches against waterbirds such as Spoonbills and Woolly-necked Storks (at Dudhwa National Park, Uttar Pradesh, India).

The Black-necked Stork is a carnivore and its diet includes water-birds such as coots, and Little Grebes, Northern Shoveller, Pheasant-tailed Jacana, a range of aquatic vertebrates including fish, amphibians and reptiles and invertebrates such as crabs and molluscs. They have also been known to prey on the eggs and hatchlings of turtles. In the Chambal river valley they have been observed to locate nests of Kachuga dhongoka buried under sand (presumably by moistness of the freshly covered nest) and prey on the eggs of the turtle. In Australia, they have been seen foraging at night feeding on emerging nestlings of marine turtles. Stomach content analyses of nine storks in Australia showed their diet to contain crabs, molluscs, insects (grasshoppers and beetles), amphibians, reptiles and birds. The storks had also consumed a small piece of plastic, pebbles, cattle dung, and plant material. Black-necked Storks fed almost exclusively on fish in wetlands located inside managed, protected areas in Australia and India.

They sometimes soar in the heat of the day or rest on their hocks. When disturbed, they may stretch out their necks. Their drinking behaviour involves bending down with open bill and scooping up water with a forward motion followed by raising the bill to swallow water. They sometimes carry water in their bill to chicks at the nest or even during nest building or egg stages.

Like other storks, they are very silent except at nest where they make bill-clattering sounds. The sounds produced are of a low-pitch and resonant and ends with a short sigh. Juveniles fledged from the nests can occasionally call using a mildly-warbling, high-pitched series of whistles, usually accompanied with open, quivering wings. These calls and behavior are directed at adult birds and are a display to solicit food, particularly in drought years when younger birds are apparently unable to find food on their own easily.

Black-necked Storks are largely non-social and are usually seen as single birds, pairs and family groups. Flocks of up to 15 storks have been observed in Australia and India, and appear to form due to local habitat conditions such as drying out of wetlands.

The Black-necked Stork is the type-host for a species of ectoparasitic Ischnoceran bird louse, Ardeicola asiaticus and a species of endoparasitic trematode Dissurus xenorhynchi.