The forest raven (Corvus tasmanicus), also known as the Tasmanian raven, is a passerine bird in the family Corvidae native to Tasmania and parts of southern Victoria, such as Wilsons Promontory and Portland. Relict populations are also found in parts of New South Wales, such as Coffs Harbour and Armidale. Measuring 50–53 cm (20–21 in) in length, it has all-black plumage, beak and legs with a white iris. Like those of the other two species of raven in Australia, its black feathers have grey bases.
Taxonomy and naming
John Latham had described the south-seas raven in 1781, with loose throat feathers and being found in "the Friendly Isles" in the South Seas, but did not give it a binomial name. Although the term refers to Tonga, the specimen resembles what is now known as the Tasmanian raven and was collected by ships' surgeon William Anderson on the Third voyage of James Cook in January 1777. Tasked with being the expedition's naturalist, Anderson had collected many bird specimens but had perished of tuberculosis in 1778 before the return home. Many collection localities were incorrect or notes were lost, and only pieced together after many years. Gmelin gave the species the name Corvus australis in the 13th edition of Systema naturae in 1788.
In his 1865 Handbook to the Birds of Australia, John Gould noted a single species of corvid in Australia, Corvus australis, which he called the white-eyed crow. He used Johann Friedrich Gmelin's 1788 name, which predated Vigors and Horsfield's description. All species were (and still are) colloquially known as crows by the general population and are difficult to distinguish. In 1912 Scottish naturalist William Robert Ogilvie-Grant clarified the species as C. coronoides (raven, and incorporating little and Tasmanian ravens) and C. cecilae (crow). Subsequently, French-American ornithologist Charles Vaurie acted as First Revisor under under Article 24 of the International Code of Zoological Nomenclature (ICZN) Code and discarded C. australis as a junior homonym—in 1788, Gmelin had used the same binomial name to describe the black nunbird—to preserve the stability of the name. This has been followed by later authors.
Gregory Mathews described the forest raven as a distinct subspecies Corvus marianae tasmanicus in 1912, its species name derived from Tasmania, the type locality. Rowley raised the forest raven to species rank in 1970, noting there were no intermediate forms between it and the little raven (its closest relative) and that it was clearly larger with a much more massive bill. He described a second subspecies—Corvus tasmanicus boreus—the same year, observing that C. tasmanicus from Tasmania and southern Victoria has a very short tail compared with individuals from the northern New South Wales population.
Preliminary genetic analysis of the genus using mitochondrial DNA showed the three raven species to belong to one lineage and the two crows to another, in the clade of Australasian species. The genetic separation between species is small and there was a suggestion the forest raven may be conspecific with the Australian raven. Subsequent multigene analysis using nuclear DNA by Jønsson and colleagues in 2012 clarified that the forest and little raven are each other's closest relative. The northern subspecies boreus turned out to be nested in the Tasmanian tasmanicus, indicating the populations separated very recently.
|Based on Jønsson et al. 2012|
Ian Rowley proposed that the common ancestor of the five species diverged into a tropical crow and temperate raven sometime after entering Australia from the north. The raven diverged into the ancestor of the forest and little ravens in the east and Australian raven in the west. As the climate was cooler and dryer, the aridity of central Australia split them entirely. Furthermore, the eastern diverged into nomadic little ravens and, in forested refuges, forest ravens. As the climate eventually became warmer, the western ravens spread eastwards and outcompeted forest ravens on mainland Australia, as evidenced by the forest raven only found in closed forest refuges on the mainland but a wider variety of habitats in Tasmania.
Rowley gave it the name forest raven in 1970. The term "crow" is colloquially applied to any or all species of Australian corvid.
The largest of the Australian corvids, the adult forest raven is 50–53 cm (20–21 in) in length with a wingspan between 91 and 113 cm and weight of approximately 650 g (1.4 lb).The plumage is a glossy black, with a blue or green sheen visible on upper plumage, there is no seasonal variation in plumage. The wings are long and broad, with the longest of its ten primary feathers (usually the seventh but occasionally the eighth) almost reaching the end of the tail when the bird is at rest. The tail is rounded or wedge-shaped, and quite short in Tasmanian populations and longer in northern New South Wales. The beak is a similar shape to that of the little raven, though more massive and heavy-set. The upper mandible, including the nares and nasal groove, is covered with bristles. The mouth and tongue are black, as are the powerful legs and feet. The tibia is fully feathered and the tarsus is long. Sexes have identical plumage, however the male is generally larger, although there is considerable overlap in size between individuals. The forest raven can be distinguished from the two species of crow occurring in Australia by the grey base of the feathers, which is white in the latter species. The demarcation between pale and black regions on the feather is gradual in the ravens and sharply delineated in the crows. Feather bases are not normally visible when observing birds in the field, but can sometimes be seen on a windy day if the feathers are ruffled. The three species of raven are more heavily set with a broader chest than the two crow species, with the forest raven the stockiest of all. Relative size of species is only useful when two species can be seen side by side, as the overlap in size is large and the difference in size small.
Juveniles (birds up to a year old) are smaller than adults, with a shorter, shallower bill, which is dark grey with some pink at the base. The gape is pink. The plumage is softer and fluffier and often has a brown tint. It generally lacks the glossy sheen of adult birds, though a blue-purple sheen can be seen sometimes on mantle and shoulders plumage. Birds between one and two years of old closely resemble adults but retain juvenile feathers on wings and tail and have smaller bills. Birds between two and three years have adult plumage but lack the adult eye colour.
Eye colour varies with age: nestlings up to four months old have blue-grey eyes, juveniles aged from four to fourteen months have brown eyes, and immature birds have hazel eyes with blue eyerings around the pupil until age two years and ten months.[a]
The call is considered the most reliable means of identification in areas where its range overlaps with other corvids, and is a deep "korr-korr-korr-korr" with a similarly drawn out last note to the Australian raven.
Distribution and habitat
The only member of the corvid family that has a permanent population in Tasmania, the forest raven is the most widely distributed bird species in the state. It inhabits a wide range of habitat within Tasmania such as woods, open interrupted forest, mountains, coastal areas, farmland and town and city fringes. It is also found in southern Victoria from Gippsland west through Wilson's Promontory and the Otway Ranges. Further west, it occurs patchily in south-east South Australia.
In its present stronghold — the state of Tasmania — the forest raven is one of only three native birds that have no legal protection outside national parks and other reserves. The other two unprotected species are the great cormorant and the little pied cormorant. All other native Tasmanian birds are listed as protected under the state's Nature Conservation Act 2002.
The forest raven was first recorded on King Island in Bass Strait in 1979, becoming more numerous and being encountered in flocks of several hundred birds by 1997. The island was previously inhabited by little ravens.
The forest raven is an omnivore, though eats more meat than smaller corvids. Its diet includes a wide range of foods such as insects, carrion, fruit, grain and earthworms. It has been known to kill and eat birds as large as the silver gull (Larus novaehollandiae) using some degree of cunning by pretending to forage near enough to get close for the kill.
The nest is constructed from twigs and lined with available materials such as leaves, wool, grass, bark or feathers. Nests are generally constructed in a similar manner to the Australian raven, high in a tall tree, however nests have been constructed on the ground in locations such as Tasmania's offshore islands where trees are not available.
The mite Knemidocoptes intermedius has been isolated from the forest raven. Infestation results in crusty (hyperkeratotic) grey lesions around their tibiotarsal joints, the mites living in tunnels under the skin.
Forest raven, Mole Creek, Tasmania, Australia
Forest raven feeding on the remains of a roadkilled kangaroo, Mole Creek, Tasmania, Australia
Forest raven, Renison Bell Conservation Reserve, Tasmania, Australia
- Rowley and colleagues recorded iris colour changes of all five Australian corvid species raised in captivity.
- BirdLife International (2013). "Corvus tasmanicus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- Latham, John (1781). A General Synopsis of Birds 1. London, United Kingdom: Benj. White. p. 369.
- Rowley, Ian (1970). "The Genus Corvus (Aves: Corvidae) in Australia". CSIRO Wildlife Research 15 (1): 27–71. doi:10.1071/CWR9700027.
- Stresemann, Erwin (The Auk). "Birds collected during Capt. James Cook's last expedition (1776-1780)". 1950 67 (1): 66–88. Check date values in:
- Gmelin, Johann Friedrich (1788). Systema naturae per regna tria naturae :secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis /Caroli a Linné. Leipzig, Germany: Impensis Georg. Emanuel. Beer. p. 365.
- Gould, John (1865). Handbook to The birds of Australia. London, United Kingdom: self. p. 475.
- Ogilvie-Grant, William Robert (1912). "The Crows of Australia". Emu 12 (1): 44–45. doi:10.1071/MU912044.
- Vaurie, Charles (1962). Mayr, Ernst, ed. Check-list of Birds of the World (XV ed.). Cambridge, Massachusetts: Harvard University Press. p. 261.
- Schodde, Richard; Mason, I. J. (1999). Directory of Australian Birds: Passerines. Collingwood, Victoria: CSIRO. p. 609. ISBN 978-0-643-10293-4.
- Higgins 2006, p. 717.
- Haring, Elisabeth; Däubl, Barbara; Pinsker, Wilhelm; Kryukov, Alexey; Gamauf, Anita (2012). "Genetic divergences and intraspeciﬁc variation in corvids of the genus Corvus (Aves: Passeriformes: Corvidae) – a ﬁrst survey based on museum specimens". Journal of Zoological Systematics and Evolutionary Research 50 (3): 230–46. doi:10.1111/j.1439-0469.2012.00664.x.
- Jønsson, Knud A.; Fabre, Pierre-Henri; Irestedt, Martin (2012). "Brains, tools, innovation and biogeography in crows and ravens". BMC Evolutionary Biology 12. doi:10.1186/1471-2148-12-72.
- Rowley, Ian; Vestjens, W.J.M. (1973). "The Comparative Ecology of Australian Corvids. VI. Why five species?". CSIRO Wildlife Research 18 (1): 157–69. doi:10.1071/CWR9730157.
- Higgins 2006, p. 727.
- Higgins 2006, p. 726.
- Higgins 2006, p. 692.
- Higgins 2006, p. 693.
- Higgins 2006, p. 694.
- Higgins 2006, p. 718.
- Thomas, R; Thomas, S; Andrew, D; McBride, A (2011). Storer, P, ed. The complete guide to finding the birds of Australia (2nd ed.). Collingwood, Victoria, Australia: CSIRO Publishing. p. 370. ISBN 9780643097858.
- Higgins 2006, p. 719.
- Higgins 2006, p. 720.
- Rowley, Ian; Vestjens, W.J.M. (1973). "The Comparative Ecology of Australian Corvids. V. Food". CSIRO Wildlife Research 18 (1): 131–55. doi:10.1071/CWR9730131.
- Mason, R.W.; Fain, A. (1988). "Knemidocoptes intermedius identified in forest ravens (Corvus tasmanicus)". Australian Veterinary Journal 65 (8): 260. doi:10.1111/j.1751-0813.1988.tb14316.x.
- Higgins, Peter Jeffrey; Peter, John M.; Cowling, S.J. (eds.) (2006). Handbook of Australian, New Zealand and Antarctic Birds. Vol. 7: Boatbill to Starlings. Melbourne, Victoria: Oxford University Press. ISBN 978-0-19-553996-7.