Bicknell's Thrush
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| Bicknell's Thrush | ||||||||||||||
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| Catharus bicknelli (Ridgway, 1882) |
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Catharus minimus bicknelli |
The Bicknell's Thrush, Catharus bicknelli, is a medium-sized thrush, at 17.5 cm (6.9 in) and 28 g (1 oz).
Adults are olive-brown on the upperparts, slightly redder on the tail. The underparts are white with gray on the flanks; the breast is greyish brown with darker spots. They have pink legs, a faint grey eye ring, and gray cheeks. They are slightly smaller than the very similar Gray-cheeked Thrush but apart from that all but indistinguishable in outward appearance. Together with this, it forms a cryptic species pair and was indeed formerly considered conspecific [1]. Bicknell's and the Gray-cheeked Thrush make up a close-knit group of migrant species together with the Veery (Winker & Pruett, 2006).
Their breeding habitat is the coniferous forests in southeastern Quebec to Nova Scotia and northern New England and New York state. It is the rarest and most secretive of the breeding thrushes in North America and it is the only breeding known to be restricted as a breeder to the Northeast of the continent. These birds are usually found at higher elevations, normally nesting above 915 m (3,000 ft).[1]
They have an unusual mating system in which females mate with more than one male. Such a mating practice is not known to occur in other thrushes.[2] As many as four males perform duties connected with one nest, including bringing food for the nestlings. They make a bulky cup nest close to the trunk of a conifer. Bicknell’s Thrush nestlings grow rapidly, developing in 12 days from peanut-sized hatchlings to completely feathered adult-sized birds. Ticks, blowflies, and lice are some of the known parasites with which Bicknell's Thrush must contend. Predators include the Sharp-shinned Hawk, the long-tailed weasel, and the Northern Saw-whet Owl. Perhaps the most important predator, however, is the red squirrel, the main confirmed predator of eggs and nestlings in breeding ecology studies.[3]
These birds migrate to the West Indies, (the Greater Antilles), with an estimated 90% of the individuals wintering on Hispaniola [2].
They mainly forage on the forest floor, mainly eating insects. It also catches flies and gleans insects from the foliage of trees. It adds wild fruit to its diet in late summer, during migration, and on the wintering grounds.
This bird's song is a jumbled series of flute-like tones ending on a higher note. They are very secretive during the nesting season.
This bird's numbers are declining in some parts of its already limited range as a result of habitat degradation. Scientists believe that industrial pollution is one of the main reasons for the decline of the red spruce, an important element in Bicknell’s Thrush habitat in the United States. They also think that airborne heavy metals have damaged high-elevation forests in the northeastern United States. Furthermore, based on expected substantial carbon dioxide increases by the end of the century, scientists predict a radical reduction of balsam fir forest in the eastern United States. Global climate change might be an even more significant force for long-term habitat degradation. If average global temperatures increase and forests change as much as predicted, Bicknell’s Thrush habitat is very likely to be altered in ways that may seriously affect the species’ survival. Other known potential threats to Bicknell’s Thrush habitat are the development of recreational skiing and summer sports areas, increasing numbers of telecommunications towers on mountaintops, cyclical spruce budworm outbreaks, and commercial forestry operations. If they are modified, industrial forestry practices, although possibly harmful, may aid in conservation efforts to protect Bicknell’s Thrush. While much more study is needed, the bird’s apparent acceptance of certain commercial second-growth forest gives promise to possibilities of “growing” Bicknell’s Thrush habitats in the future. There is also considerable concern about the degradation of Bicknell’s Thrush’s wintering habitats. The Dominican Republic’s native forests are under considerable pressure from naturally occurring events such as hurricanes, as well as changes for agricultural activities, particularly at low altitudes. The forested lands of Haiti have been almost completely eliminated. In Cuba, most of the known suitable habitat exists in protected parklands.[4]
This bird was named after Eugene Bicknell, an American amateur ornithologist, who discovered the species on Slide Mountain in the Catskills in the late 19th century.
[edit] References
- ^ http://www.fws.gov/r5gomp/gom/habitatstudy/metadata/Bicknell's_thrush_model.htm
- ^ http://www.hww.ca/hww2.asp?cid=7&id=28
- ^ http://www.hww.ca/hww2.asp?cid=7&id=28
- ^ http://www.hww.ca/hww2.asp?cid=7&id=28
- BirdLife International (2004). Catharus bicknelli. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. RangeMap Database entry includes a range map and justification for why this species is vulnerable.
- Winker, Kevin & Pruett, Christin L. (2006): Seasonal migration, speciation, and morphological convergence in the avian genus Catharus (Turdidae). Auk 123(4): 1052-1068. [Article in English with Spanish abstract] DOI: 10.1642/0004-8038(2006)123[1052:SMSAMC]2.0.CO;2 PDF fulltext
[edit] External links
- Environment Canada: Bicknell's Thrush
- Hinterland Who's Who: Bicknell's Thrush
- Cornell Lab of Ornithology All About Birds Bird Guide: Bicknell's Thrush
- Bicknell's Thrush photo gallery VIREO
- IUCN Bicknell's Thrush rangemap
[edit] Bibliography
- Environmnent Canada: Bicknell's Thrush: Bibliography
