Red Knot Calidris canutus Scientific name definitions

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 Piersma, T. and N. C. Davidson. (1992). The migrations and annual cycles of five subspecies of knots in perspective. Wader Study Group Bulletin 64 (Suppl.):187-197. Close , Buehler and Piersma 2008 Buehler, D. M. and T. Piersma. (2008). Travelling on a budget: Predictions and ecological evidence for bottlenecks in the annual cycle of long-distance migrants. Royal Society Philosophical Transactions Biological Sciences 363 (1490):247-266. Close ).

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, P. S. and M. Soloviev. (1996). Distribution, migrations and biometrics of knots Calidris canutus canutus on Taimyr, Siberia. Ardea 84:85-98. Close , Tomkovich and Dondua 2008) and spends winter in some of the hottest (Wolff and Smit 1990 Wolff, W. J. and C. J. Smit. (1990). The Banc d'Arguin, Mauritania, as an environment for coastal birds. Ardea 78:17-38. Close ). It has been a key species for understanding relationships between ecological physiology and migration energetics (Gudmundsson et al. 1991 Gudmundsson, G. A., A. Lindstrom and T. Alerstam. (1991). Optimal fat loads and long-distance flights by migrating Knots Calidris canutus, Sanderlings C. alba and Turnstones Arenaria interpres. Ibis 133:140-152. Close ; Piersma et al. Piersma et al. 1994 Piersma, T., Y. Verkuil and I. Tulp. (1994). Resources for long-distance migration of knots Calidris canutus islandica and C-c-canutus: How broad is the temporal exploitation window of benthic prey in the western and eastern Wadden Sea? Oikos 71:393-407. Close , Piersma et al. 1995a Piersma, T., N. Cade and S. Daan. (1995a). Seasonality in basal metabolic rate and thermal conductance in a long-distance migrant shorebird, the knot (Calidris canutus). Journal of Comparative Physiology B Biochemical Systemic and Environmental Physiology 165:37-45. Close , Piersma 2002), as well as the development of migration strategies (Piersma Piersma 1991 Piersma, T. (1991). Red Knots in New Zealand eat molluscs too: preliminary diet observations at Miranda, Firth of Thames and Farewell Spit in November 1990. The Stilt 19:30-35. Close , Piersma 1998 Piersma, T. (1998). Phenotypic flexibility during migration: optimization of organ size contingent on the risks and rewards of fueling and flight. Journal of Avian Biology 29:511-520. Close ; Wiersma and Piersma 1994 Wiersma, P. and T. Piersma. (1994). Effects of microhabitat, flocking, climate, and migratory goal on energy expenditure in the annual cycle of Red Knots. Condor 96:257-279. Close ).

Knots have also been a focal research species for development of conservation strategies for long-distance migrants (Myers et al. 1987 Myers, J. P., R. I. G. Morrison, P. Z. Antas, B. A. Harrington and T. E. Lovejoy. (1987). Conservation strategy for migrating species. American Scientist 75:19-26. Close , Harrington and Flowers 1996 Harrington, B. and C. Flowers. (1996). The flight of the Red Knot. New York: W. W. Norton. Close , Piersma and Baker 2000 Piersma, T. and A. Baker. (2000). "Life history characteristics and the conservation of migratory shorebirds." In Behavior and conservation., edited by L. Gosling and W. Sutherland, 105-124. Cambridge, U.K: Cambridge Univ. Press. Close ), including development of the Western Hemisphere Shorebird Reserve Network (Bildstein et al. 1991 Bildstein, K. L., G. T. Bancroft, P. J. Dugan, D. H. Gordon and R. M. Erwin. (1991). Approaches to the conservation of coastal wetlands in the Western Hemisphere. Wilson Bulletin 103:218-254. Close ) and the Global Flyway Network that seeks to integrate research and conservation across all the major flyways in the world.