Island Thrush
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| Turdus poliocephalus Latham, 1802 |
The Island Thrush, (Turdus poliocephalus) is a common and highly variable forest bird from the thrush family. Almost 50 subspecies have been described from Taiwan to Samoa, and exhibiting a great deal of variation in plumage. Several subspecies are threatened and three have already become extinct.
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[edit] Taxonomy
The Island Thrush is a member of the cosmopolitan genus Turdus (Linnaeus, 1758), one of the most widely distributed bird genera in the world. The taxonomy of the Island Thrush is a great deal more complex, and has defied attempts to split the group based on the four suspected morphological types. One subspecies, Turdus poliocephalus niveiceps, from Taiwan, represents the most distinct taxa and may be a separate species. It lives at the northerly range of the species, and is the only subspecies to exhibit sexual dimorphism. There are also thought to be at least two subspecies as yet undescribed by science, both from the Indonesian island of Sulawesi.
[edit] Distribution
The Island Thrush is widely but patchily distributed across its range. It is present islands in Samoa, Fiji, Vanuatu, New Caledonia, the Solomon Islands, New Guinea and surrounding islands, many Indonesian islands, the Philippines and Taiwan. It is, however, restricted to areas with bird communities of less than 25-35 species. On the larger islands, like Borneo or New Guinea, this has meant that it is only found at high altitudes, above 2750m. On smaller islands, which can support only much smaller bird communities they may be found at lower altitudes. Two or more subspecies may exist on islands, with each species living in different habitats. Many subspecies have very small ranges that may be as small as one island (like the Kadavu subspecies).
[edit] Description
The 49 subspecies of Island Thrush vary dramatically in appearance, but all resemble a typical Turdus thrush and have a yellow bill, eye-ring and legs. The Samoan subspecies, T. p. samoensis, is identical in appearance to the Blackbird of Europe, whereas the T. p. seebohmi of northern Borneo is dark above with a red breast and resembles and American Robin. Some subspecies, including the male (but not female) T. p. niveiceps have entirely white heads, but the Kadavu form T. p. ruficeps has an entirely orange head.
[edit] Behaviour
[edit] Diet
The Island Thrush has a very catholic diet, taking a range of invertebrates such as insects (mostly beetles), spiders, snails, earthworms, as well as carrion and even small reptiles. It will, depending on what is locally available, also take fruit and seeds. Its foraging technique is described as similar to that of the Common Blackbird, investigating the leaf litter and low branches in dense cover, but in some places will also forage in the canopy.
[edit] Breeding
Most Island Thrushes breed in discreet 2-3 month seasons (the precise timing varies depending on location), the exception are the birds in Fiji which nest from June until January. They nest in a well constructed cup well hidden in dense vegetation, laying between one to three eggs.
[edit] Conservation
As a species the Island Thrush is not threatened, and many subspecies are locally very common. Several subspecies are threatened, T. p. erythropleurus considered critically so. The race found on Christmas Island, it is threatened by the introduced yellow crazy ant, which is capable of killing nestlings. Several other subspecies have declining ranges, including T. p. xanthopus from New Caledonia (now extinct from Grande Terre and restricted to 100 individuals surviving only on Yande and Neba) and T. p. samoensis from Samoa.
Three subspecies have become extinct, T. p. vinitincus from Lord Howe Island, T. p. mareensis from the Loyalty Islands and the nominate race T. p. poliocephalus from Norfolk Island. T. p. poliocephalus was relatively common as recently as 1941, but introduced Black Rats, habitat loss and hybridization with self-introduced Common Blackbirds caused it to be extinct by 1975.
[edit] References
- BirdLife International (2004). Turdus poliocephalus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
- Collar, N. J. (2005) Family Turdidae (Thrushes) Pp. 514-811 in: del Hoyo. J., Elliott, A., Sargatal, J., (eds), Handbook of the Birds of the World, Volume Ten, Cuckoo-shrikes to Thrushes, ISBN 84-87334-72-5
