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Red Knot
Calidris canutus
Order
CHARADRIIFORMES
– Family
SCOLOPACIDAE
Authors: Harrington, Brian A.
Revisors: Baker, Allan, Patricia Gonzalez, and R.I.G. Morrison

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Introduction

Adult Red Knot, Alaskan ssp., on breeding grounds, Seward Peninsula, AK, June.
Figure 1. Distribution of the Red Knot in North and Middle America.

The largest calidridine sandpiper of North America, and in the genus Calidris exceeded in size only by the Great Knot (C. tenuirostris), the Red Knot is rusty-red in breeding plumage, changing to dull gray dorsally and white ventrally in Basic (winter) plumage, with few distinct markings. This species is a Holarctic breeder, mainly in middle- and high-arctic zones, with 3 subspecies (islandica, rufa, and roselaari) distributed in the Nearctic from Greenland to northern Alaska. The nominate subspecies nests in central Russia (e.g., the northern Taymyr Peninsula), C. c. piersmai in the New Siberian Islands, C. c. rogersi in eastern Russia (e.g., Chukchi Peninsula), and C. c. roselaari on Wrangel Island and in northern Alaska. This account focuses largely on the Western Hemisphere subspecies.

Red Knots are noted for their extraordinary long-distance migrations -- up to 15,000 km between circumpolar breeding habitats and marine wintering habitats in southern latitudes of South America, Africa, Europe, Australia and New Zealand. Population sizes for knots are in decline around the world, especially C. c. rufa, which declined from about 82,000 individuals in the 1980s to fewer than 30,000 in 2010.

This is a monogamous and single-brooded species, and like most other northern shorebirds typically lays a 4-egg clutch. Courtship is accompanied by elaborate flight, ground, and vocal displays. For nesting, this knot prefers drier tundra and sparsely vegetated gravel ridges.

Red Knots are principally marine shorebirds in the non-breeding season, when they feed on polychaete worms, small crabs, and marine mollusks, especially bivalves that they swallow whole and crush in their muscular gizzard. During spring migration, however, large flocks gorge on the eggs of horseshoe crabs (Limulus) that come ashore to spawn in late May at the penultimate stopover site in Delaware Bay – along the mid-Atlantic coast of the USA. Recent studies of Red Knots fitted with geolocators identified a final stopover at Nelson River in Hudson Bay, before the birds move on to breeding sites in the high Arctic.

Research on Red Knots has focused primarily on distribution and taxonomy, long-distance migration, breeding behavior, foraging ecology, physiological adaptations, phenotypic flexibility, population demography, and conservation {e.g. Atkinson et al. 2007, Gonzalez et al. 2005, Piersma et al. 2005, Van Gils et al. 2005). The species currently consists of 6 recognized subspecies that breed around arctic polar regions of the earth, each showing slightly different physical features but having strikingly different migration strategies (Piersma and Davidson 1992).

The Red Knot is thus an apt species for studying the development of avian migration. It breeds in some of the coldest regions of the earth (Tomkovich and Soloviev 1996, Tomkovich and Dondua 2008) and spends winter in some of the hottest (Wolff and Smit 1990). It has been a key species for understanding relationships between ecological physiology and migration energetics (Gudmundsson et al. 1991; Piersma et al. 1994, 1995a, Piersma 2002), as well as the development of migration strategies (Piersma 1991, 1998; Wiersma and Piersma 1994).

Knots have also been a focal research species for development of conservation strategies for long-distance migrants (Myers et al. 1987, Harrington 1996, Piersma and Baker 2000), including development of the Western Hemisphere Shorebird Reserve Network (Bildstein et al. 1991) and the Global Flyway Network that seeks to integrate research and conservation across all the major flyways in the world.