The Torresian crow (Corvus orru), also called the Australian crow or Papuan crow, is a passerine bird in the crow family native to the north and west of Australia and nearby islands in Indonesia and Papua New Guinea. The species has a black plumage, beak and mouth with white irises. The base of the feathers on the head and neck are white. The Torresian crow is slightly larger with a more robust bill than the morphologically similar little crow.
Although widespread over northern Australia and some nearby islands, the common name "Torresian" refers to the Australian Shire of Torres.
Taxonomy
thumb|Near Beaudesert - Australia
The Torresian crow was described by the French ornithologist Charles Lucien Bonaparte in 1850. The origin of the specific epithet orru is not known but may be derived from a Papuan name.
There are three subspecies:
- C. o. latirostris Meyer, AB, 1884 – east Lesser Sunda Islands
- C. o. orru Bonaparte, 1850 – Maluku Islands, New Guinea, D'Entrecasteaux Islands. and Louisiade Archipelago
- C. o. cecilae Mathews, 1912 – west, central and northern Australia
The Bismarck crow (Corvus insularis) on the Bismarck Archipelago was formerly considered a subspecies. In Central Australia southwest of Alice Springs, the Pitjantjatjara term for race ceciliae is kaa<u>n</u>ka. The term wati kaa<u>n</u>ka refers to a light-fingered man or someone who hangs around suspiciously.
Description
The Torresian crow is a large corvid, about the same size (48–53 cm in length) as the Eurasian carrion crow but with a more robust bill and slightly longer legs. The plumage of the Torresian crow is glossy black on the back and dull black on the breast with inconspicuous throat hackles. Its tail is broad and has a distinctive square-shaped tip. Its bill is dark grey and about the same length as the head. The legs and feet are a similar dark grey color with pink foot soles. The Torresian crow has the typical white iris of the other Australasian Corvus species with a fine, blue eye-ring. However, it can be distinguished from most except the little crow by the base of the head and neck feathers being white. The white feather bases are revealed when ruffled. Birds of this species characteristically shuffle their wings after alighting. Sexes are identical in their appearance; however, juveniles lack glossy dorsal feathers and have blue eyes, rather than white, up to about nine months of age.
The Torresian crow is not to be confused with the Australian raven the juveniles of which have a similar appearance. Adult ravens have distinctive long throat hackles which may not be visible in some postures. Despite their visual similarities, the Australian raven and crow have different and unique calls.
Distribution and habitat
The Torresian crow has an extensive distribution across Australia, Papua New Guinea in particular the Bismarck Archipelago and some islands in Indonesia, in particular the Moluccas. The range of the mainland Australian race C. orru ceciliae extends from the tropical north of Australia to as far south as Forster on the east coast of New South Wales and to between Geraldton and Norseman in South Western Australia.
The Torresian crow occupies almost any habitat within its geographic range where there is a permanent source of water. The species is common in habitats such as tropical rainforests, eucalyptus woodland, open scrub, beaches, swamps, offshore islands. The Torresian crow is also well adapted to fringe habitats including farmland, towns and cities. On farms in much of Northern Australia, they are the most numerous bird species and are considered a pest by farmers, as they damage crops such as sweetcorn, peanuts, wheat and many kinds of fruit. Torresian crows are common in urban landscapes and many cities and towns in Australia support large populations. In the arid zones of central Australia, the species is sparsely distributed and confined to areas with permanent water.
Two other races occur on various islands to the north: C. orru orru in Papua New Guinea and the Moluccas), and C. orru latirostris on Tanimbar and Babar Islands.
Ecology
Expansion of the Torresian crow population in Australia
The Torresian crow, similarly to many corvids, is an opportunistic species and has adapted to a broad range of habitats. The population size of Torresian crows in Australia is increasing, possibly owing to the expansion of agricultural activity in arid areas, as well as increased urbanization. Studies on the distribution of Torresian Crows across Australia, between 1993 and 2004, have shown that the geographic range of the species has expanded into highly urbanized regions including many of Australia's largest cities, as well as further south into arid areas of central Australia. The continued urban growth of Australia in the past decades has resulted in large areas of natural subtropical and eucalypt sclerophyll forest to be replaced by suburbs and parkland, especially in the regions surrounding major cities. This increased urbanisation of land has been associated with the observed proliferation of Torresian crows.
One of the reasons the Torresian crow is able to take advantage of increased urbanisation is its diet; a significant proportion of the diet of the species consists of carrion, which is abundant in urban environments due to road kill. Anthropogenic waste also provides Torresian crows with a plentiful source of food requiring minimal foraging. Furthermore, food resources of the Torresian crow may be indirectly supplemented by the modification of land coverage, where native forests are replaced by lawns and parkland that are rich in invertebrates which also represent a significant part of the species' diet. and to feed on poisonous prey without ingesting poison (see below) among other behaviours. Torresian crows are large and aggressive birds, with females displaying the more aggressive behaviour and dominating most other species except large birds of prey and the Australian magpie. They have been observed to attack larger birds of prey, particularly wedge-tailed eagles and most owl species in defence of their nest or territory.
Diet
Torresian crows are omnivores and consume a wide range of foods. Their diet varies significantly between habitats with birds living in urban environments relying to a greater extent on anthropogenically related food sources compared to those living in natural habitats. Outside urbanised areas, the diet of Torresian crows primarily consists of invertebrates, berries and carrion.
Nesting
The main breeding period occurs from August to January, with most eggs being laid in September and October. The stick nest is built high in a tree, usually a eucalypt, however other locations such as power pylons and tall buildings are occasionally chosen. Two to four eggs are laid which the female incubates for roughly twenty days and then is assisted by the male in rearing the chicks for around forty days until they leave the nest.