Oriental Darter - Behaviour and Ecology

Behaviour and Ecology

The Oriental Darter is found mainly in freshwater lakes and streams. They usually forage singly, with the entire body submerged, swimming slowly forward using their webbed feet while the head and neck is moved jerkily abovethe water. It darts its neck to impale fish and then brings them out of water, tossing them into the air before swallowing the fish head first. They may sometimes be found along with cormorants that share the habit of spreading out their wings to dry when perched on a waterside rock or tree. They sometimes soar on thermals during the warm part of the day but will alternate flapping and gliding in normal flight.

They nest in mixed species heronries where they build a stick platform on the nest tree which is usually surrounded by water. Several pairs may nest close to each other. The branch is flattened by the birds prior to the placement of the sticks that form the nest platform. The nest sites are defended from other birds with posturing and thrusts of the neck. The breeding season is June to August (during the rainy season) in northern India, April–May in southwestern India and in winter in southeastern India (during the northeast monsoon). The usual clutch consists of 3 to 6 spindle shaped bluish-green eggs with a white chalky covering that gets soiled over time. Both parents incubate the eggs, beginning after the first egg is laid which leads to asynchronous hatching of the young. The newly hatched chicks are bare and covered with some down on the head. As they grow, they become covered in white down. The chicks feed by thrusting their heads into the throat of their parents.

Adults go through a synchronous moult of their flight feathers after the breeding season resulting in the loss of flying ability for a brief period of time. When disturbed from their perches during this period, they dive into the water below and attempt to escape underwater. This escape behaviour is also employed by chicks at the nest. They are very silent except at the nest where they produce grunts and croaks and a disyllabic chigi-chigi-chigi. Chicks are noisy when begging for food. Adults roost communally in trees close to or over water.

Chicks, especially those more than half grown are sometimes preyed on by raptors such as Pallas's Fish Eagle (Haliaetus leucoryphus). The long scapular feathers were once popular for use in decorating hats. A number of parasites have been recorded from adult birds including Schwartzitrema anhingi (Trematoda), Petasiger nicolli, Mesorchis pendulus, and Echinorhynchotaenia tritesticulata (Cestoda:Dilepididae).

In some parts of northeastern India, darters were (or are) used by tribals to capture fish from streams. A ring is tied around the neck to prevent them from swallowing the prey just as is done with cormorant fishing in parts of Southeast Asia.