Great knot (Calidris tenuirostris)
|Size||Length: 27 cm (2) (3)|
|Weight||55 g (2) (3)|
The great knot is classified as Vulnerable (VU) on the IUCN Red List (1).
The great knot (Calidris tenuirostris) is a long distance migratory shorebird, with a rather plump body and a stout, straight bill (4). For most of the year, the great knot has streaky, greyish-brown feathers on its upperparts and head, and white underparts (5). During flight, a white stripe on the wings and a small, whitish patch on the rump can be seen (5). During the breeding season, it develops reddish-brown streaks on its back, and black streaks on the head and breast (5). The bill is black, the irises are brown, and the legs and feet are dark grey to olive green (4). While usually silent, the great knot may occasionally call with a ‘prrt’ sound (2).
The great knot breeds in north-eastern Siberia (Russia) and winters along the coastlines of Southeast Asia, Australia, India, Bangladesh, Pakistan and the eastern shores of the Arabian Peninsula (6).
During the breeding season, the great knot is found on high altitude plateaus between 300 and 1,600 metres above sea level, particularly on gravelly areas covered with lichen and patches of herbs and heather (6). In winter, the great knot inhabits a variety of sheltered coastal habitats, including mudflats, bays, harbours, estuaries and lagoons with intertidal flats and creeks, and sandy spits (2) (3) (6), and it roosts in sheltered areas which are not disturbed by tides (6).
The great knot begins reproducing at around two years of age (7). Breeding takes place between late May and late July (6), when the female typically lays four eggs (7). The eggs generally hatch between mid-June and mid-July after an incubation period of about 22 days (7).
After breeding, the great knot departs the breeding grounds and begins its migration south to warmer wintering grounds, which it normally arrives at between August and October (6). Often travelling in mixed flocks with other knot and turnstone species (Arenaria), the great knot relies on stop-over sites during the long journey, where it can feed and restore its energy, enabling the bird to continue with its migration (6) (8).
During the breeding season, adult great knots feed on berries from plants such as Empetrum, Dryas and Vaccinium species, and the kernels of dwarf pine, while young great knots feed exclusively on insects and spiders. During the winter, when inhabiting coastal areas, and when stopping over on its lengthy migration, the great knot may also consume a variety of other animals, such as bivalves, gastropods, sea cucumbers, crabs and shrimps (6) (7), and can be seen methodically thrusting its bill deep into the mud to search for these coastal invertebrates (4). When migrating, large flocks of up to several thousand individuals may forage together, while at the wintering site, the great knot typically forages in small groups (6).
The main threat to the great knot is the degradation and loss of its habitat, as a result of pollution, reduced river flows, and human disturbance, particularly in the Yellow Sea region which is an important stop-over area for this species during its migration (6). Some important stop-over sites have already been eliminated (6), such as in South Korea, where the reclamation of 40,000 hectares of tidal flats at Saemangeum is thought to have reduced the global population of great knots by up to 20 percent (9). Other stop-over sites are threatened by the construction of tidal barrages and power plants, and the expansion of industrial and urban areas (6).
The loss of important stop-over sites, and resultant population decline, has led to the great knot recently being declared at risk of extinction (6). There are limited conservation measures currently in place, such as a monitoring scheme in Australia, but further actions have been proposed; these include preventing the reclamation of critical stop-over sites, restoring those sites that have already been reclaimed, and implementing legal protection in all the countries in which it is found (6).
Learn more about the conservation of shorebirds:
International Wader Study Group:
For more information on the great knot and other bird species:
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- Bivalves: a group of aquatic molluscs that possess a shell comprised of two halves, connected by a hinge. Includes mussels, clams and oysters.
- Gastropods: a group of molluscs that have a well-defined head, an unsegmented body and a broad, flat foot. They can possess a single, usually coiled shell or no shell at all. Includes slugs, snails and limpets.
- Incubation: the act of incubating eggs, that is, keeping them warm so that development is possible.
- Intertidal: situated in the intertidal zone, the region between the high tide mark and low tide mark.
- Invertebrates: animals with no backbone, such as insects, crustaceans, worms, molluscs, and spiders.
- Lichen: a composite organism made up of a fungus in a co-operative partnership with an alga. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. Characteristically forms a crustlike or branching growth on rocks or tree trunks.
IUCN Red List (May, 2011)
- Porter, R.F., Christensen, S. and Schiermacker-Hansen, P. (2004) Birds of the Middle East. Helm Field Guides, London.
- Grimett, R., Inskipp, C. and Inskipp, T. (1998) Birds of the Indian Sub-Continent. Oxford University Press, Oxford.
- Threatened Species Unit (1999) Threatened Species Information: Great Knot. NSW National Parks and Wildlife Service, Hurstville, New South Wales.
- Grewall, B., Garvey, B. and Pfister, O. (2002) A Photographic Guide to the Birds of India. Princeton University Press, Princeton, New Jersey.
BirdLife International (June, 2010)
- Tomkovich, P. (1996) A third report on the biology of the great knot Calidris tenuirostris on the breeding grounds. The Stilt, 28: 43-45.
- Battley. P.F., Dietz, M.W., Piersma, T., Dekinga, A., Tang, S. and Hulsman, K. (2001) Is long-distance bird flight equivalent to a high energy fast? Body composition changes in freely migrating and captive fasting great knots. Physiological and Biochemical Zoology, 74(3): 435-449.
- Herkenrath, P. (2009) Conservation news: Ramsar Convention on Wetlands: 10thConference of the Parties. Oryx, 43(2): 170-171.