Red knot (Calidris canutus)
|Size||Length: 23 – 25 cm (2)|
Wingspan: 45 – 54 cm (2)
|Weight||85 – 220 g (2)|
The red knot is classified as Least Concern (LC) on the IUCN Red List (1), and listed under Appendix II of the Convention on Migratory Species (3). It is also listed under Annex II of the African-Eurasian Waterbird Agreement (AEWA) (4).
The red knot has a more conspicuous plumage during the breeding season than in the winter months. The bill is long, thick, straight and black, and the legs are black or dull green. Throughout the winter, the upperparts are pale grey with blackish primaries and a white stripe across the wing. The head is grey, with white areas above the eye and on the throat. The breast and tail are pale grey, but the flanks, belly and undertail feathers are white. However, during the breeding season the head becomes reddish with brownish mottling on the forehead, crown and back of the neck. The underparts also become red, and the tail develops a dark grey-brown stripe. Juveniles are varying shades of grey with dark edgings on the feathers, a white stripe across the wings and dark grey primaries (2) (5). Following migration the usually plump body is considerably leaner (6).
Six subspecies of the red knot are recognised, all of which breed on the Northern tundra areas and winter at temperate or tropical coastal areas. The American subspecies (Calidris canutus rufa) has the longest migration route, breeding in the Canadianarctic and flying via the eastern American coast to Patagonia and Terra del Fuego. The other American subspecies (C. c. rooselari) breeds in Alaska and winters in Florida. The C. c. islandica subspecies breeds in Canada and Greenland and winters in Europe along the coasts of the United Kingdom, France and the Wadden Sea. C. c. canutus breeds in West-Siberia and flies via Europe to West- and South-Africa, where the mudflats of the Banc d’Arguin in Mauritania are an important wintering area. The last two subspecies both breed in eastern Siberia and migrate south via the Chinese and Korean coasts; C. c. piersmai winters in north-west Australia and C. c. rogersi winters in New Zealand (2).
The red knot breeds on tundra. Stopover and winter areas are preferably large tidal mudflats, but include also rocky shores and beaches (2) (7).
The red knot is a long-distance migrant, covering between 5,000 and 15,000 kilometres, and stopping at least once along the way to feed and build up body fat and protein stores. It probes amongst the sand of estuaries and on shorelines for intertidal invertebrates, mainly small molluscs, but feeds also on crustaceans, horseshoe crab eggs and insects (2). Molluscs are ingested whole and cracked with their muscular gizzard. The size of its gizzard varies flexibly throughout the year, as a consequence of energetic demands and food quality (8). Red knots have unique sensory organs in their bill tips enabling them to detect buried prey without touching them, via water pressure differences in the sediment (comparable to the echolocation of bats) (9). Knots often form mixed species flocks with other shorebird species such as godwits (Limosa species), dunlins (Calidris alpina) and dowitchers (Limnodromus species) (5).
Breeding in the tundra of the Arctic Circle, the red knot constructs a nest in a dip between lichen-covered rocks and lays three to four buff-coloured eggs spotted with brown. Both sexes incubate the eggs for 21 to 22 days, but the female departs immediately after hatching. The male takes care of the chicks up to fledging, which takes 18 to 20 days, and then leaves the tundra before the young, to head south to the wintering grounds. At the tundra, knots eat insects, beetles, spiders, small crustaceans, snails and worms (2).
The red knot was once the most numerous shorebird in North America, but during the 1800s and early 1900s, it was put under severe hunting pressure on its migration routes (5), becoming far less common. However, the decline has continued despite a massive drop in hunting. Numbers fell in New Jersey from 90,000 in 1989 to 36,000 in 2001, and other counts suggest declines of at least 30 percent in the last 12 years. Whilst this decline in North America is not fully understood, it is thought to be related to the decline in horseshoe crabs, the eggs of which are consumed by migrating red knots (10) (11).
Other subspecies also show a serious decline in numbers. As with the American subspecies, this is often thought to be related to declines in prey species, numbers and quality in the wintering and/or stopover areas. For example, it has been shown that shellfisheries in the Wadden Sea negatively affected the survival of red knots (12).
Listed as a high priority species on the U.S. National Shorebird Conservation Plan, the red knot is also a U.S. Fish and Wildlife Service species of conservation significance, and is on the Audubon WatchList, which aims to encourage people to help reduce the decline of bird species at risk of extinction (10).
For further information on the red knot see:
Canada’s Aquatic Environments:
BBC Wildlife Finder:
For more information on this and other bird species please see:
BirdLife International - Red knot:
Authenticated (24/06/08) by Maurine Dietz, Senior Scientist, Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen,
http://www.rug.nl/biologie/onderzoek/onderzoekgroepen/dieroecologie/index; and by Jan van Gils, Department of Marine Ecology, Royal Netherlands Institute for Sea Research (NIOZ),
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
- Echolocation: detecting objects by reflected sound. Used by bats and odontocete cetaceans (toothed whales, dolphins and porpoises) for orientation and to detect and locate prey.
- Invertebrates: animals with no backbone.
- Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Mudflats: A large area where parts of the sea bottom fall dry at low tides and thus become available for birds to forage on. A good example is the Wadden Sea (in the Netherlands, Germany and Denmark). These unique tidal areas are very rare in the world and in general very important for coastal foraging birds.
- Muscular gizzard: in birds, the stomach can be divided in two parts. The first part is the glandular stomach that secrets digestive enzymes; the second part is the muscular gizzard that mechanically processes food. Depending on species and diet, some parts of the stomach can be more important. In knots, the glandular stomach is relatively unimportant. For the largest part of the year (outside the breeding season), food processing depends largely on the muscular gizzard that crushes the shells or other hard parts of the food. In knots, the actual digestion takes place in the intestines.
- Primaries: in birds, the outer flight feathers.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Tundra: treeless grassland between the icecap and the tree line of Arctic regions, with vegetation consisting of lichens, grasses, sedges and dwarf woody plants.
IUCN Red List (June, 2008)
- del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
CMS (June, 2008)
AEWA (June, 2008)
Canada’s Aquatic Environments (December, 2004)
Bird Guides (December, 2004)
Enature (December, 2004)
- Van Gils, J.A., Piersma, T., Dekinga, A. and Battley, P.F. (2006) Modelling phenotypic flexibility: an optimality analysis of gizzard size in red knots (Calidris canutus). Ardea, 94: 409 - 420.
- Piersma, T., van Aelst, R., Kurk, K., Berkhoudt, H. and Maas, L.R.M. (1998) A new pressure sensory mechanism for prey detection in birds: the use of principles of seabed dynamics?. Proceeding of the Royal Society of London, Series B, 265: 1377 - 1383.
State of New Jersey (December, 2004)
- Baker, A.J., González, P.M., Piersma, T., Niles, L.J., De Lima Serrano do Nascimento, I., Atkinson, P.W., Clark, N.A., Minton, C.D.T., Peck, M.K. and Aarts, G. (2004) Rapid population decline in red knots: fitness consequences of decreased refuelling rates and late arrival in Delaware Bay. Proceeding of the Royal Society of London, Series B, 271: 875 - 882.
- Van Gils, J.A., Piersma, T., Dekinga, A., Spaans, B. and Kraan, C. (2006) Shellfish dredging pushes a flexible avian top predator out of a marine protected area. PLoS Biology, 4: 2399 - 2404.