Sgarza indiana

Identificazione

Indian pond herons are stocky with short necks, short thick bills and buff-brown backs. In summer, adults have long neck feathers. Their appearance is transformed from dull colours when they take to flight and the white of the wings makes them very prominent. They are very similar to the squacco herons, Ardeola ralloides, but darker backed. To the east of their range, they are replaced by the Chinese pond herons, Ardeola bacchus.<p>During the breeding season, there are records of individuals with red legs. The numbers do not suggest that this is a normal change for adults during the breeding season and some have suggested the possibility of it being genetic variants.<p>Erythristic plumage has been noted. The race phillipsi has been suggested for the populations found in the Maldives, without much acceptance. It forms a superspecies with the closely related Chinese pond heron, Javan pond heron and the Madagascar pond heron.[citation needed]<p>They are usually silent but may make a harsh croak in alarm when flushed or near their nests.<p>This bird was first described by Colonel W. H. Sykes in 1832 and given its scientific name in honour of John Edward Gray. Karyology studies indicate that pond herons have 68 chromosomes (2N).

Tassonomia

Nome scientifico

Ardeola grayii

Autorità

(Sykes, 1832)

Ordine

Pelecaniformi

Famiglia

Ardeidae

Genere

Ardeola

Areale e habitat

Migrazione

Resident species

Comportamento

They are very common in India, and are usually solitary foragers but numbers of them may sometimes feed in close proximity during the dry seasons when small wetlands have a high concentration of prey. They are semi-colonial breeders. They may also forage at garbage heaps. During dry seasons, they sometimes take to foraging on well watered lawns or even dry grassland. When foraging, they allow close approach and flush only at close range. They sometimes form communal roosts, often in avenue trees over busy urban areas.<p>The Indian pond heron's feeding habitat is marshy wetlands. They usually feed at the edge of ponds but make extensive use of floating vegetation such as water hyacinth to access deeper water. They may also on occasion swim on water or fish from the air and land in deeper waters. They have also been observed to fly and capture fishes leaping out of water. Sometimes, they fly low over water to drive frogs and fishes towards the shore before settling along the shoreline. They have been noted to pick up crumbs of bread and drop them on the water surface to bait fishes.<p>The primary food of these birds includes crustaceans, aquatic insects, fishes, tadpoles and sometimes leeches (Herpobdelloides sp.). Outside wetlands, these herons feed on insects (including crickets, dragonflies and bees), fish (Barilius noted as important in a study in Chandigarh) and amphibians.<p>The breeding season begins with the onset of the monsoons. They nest in small colonies, often with other wading birds, usually on platforms of sticks in trees or shrubs. Most nests are built at a height of about 9 to 10 m in large leafy trees. The nest material is collected by the male while the female builds the nest. Three to five eggs are laid. The eggs hatch asynchronously, taking 18 to 24 days to hatch. Both parents feed the young. Fish are the main diet fed to young. Nest sites that are not disturbed may be reused year after year.<p>They have few predators but injured birds may be taken by birds of prey.<p>An arbovirus that causes "Balagodu", trematodes and several other parasites have been isolated from the species. Antibodies to Japanese encephalitis and West Nile virus has been detected in pond herons and cattle egrets from southern India. Traces of heavy metals acquired from feeding in polluted waters may be particularly concentrated in the tail feathers.

Conservazione

Tendenza della popolazione

unknown