The red knot or just knot (Calidris canutus) is a medium-sized shorebird which breeds in tundra and the Arctic Cordillera in the far north of Canada, Europe, and Russia. It is a large member of the Calidris sandpipers, second only to the great knot. Another etymology is that the name is onomatopoeic, based on the bird's grunting call note. Another, tagged "B95" and nicknamed 'Moonbird', of the subspecies C. c. rufa, was at least 20 years old as of his last sighting in May 2014. gastropods and small crabs that are ingested whole and crushed by a muscular stomach. They are able to detect molluscs buried under wet sand from changes in the pressure of water that they sense using Herbst corpuscles in their bill. Red knots travel "in larger flocks than do most shorebirds" flying " from south to north every [northern hemisphere] spring and repeat the trip in reverse every autumn". Other stopover spots in the US include islands off the coast of Massachusetts, Virginia, South Carolina, and Georgia. Fewer red knots undergo overland migration routes and winter on the Gulf Coast. Stopover areas on this route are found in the Mississippi river drainage, Northern U.S. saline lakes, and plains in Southern Canada.

Dependence on horseshoe crab eggs as food source

Red knots undergo various physiological changes before their migration to account for the physical demand of the long expedition: "flight muscle mass increases, while leg muscle mass decreases. Stomach and gizzard masses decrease, while fat mass increases by more than 50 percent". They arrive at stopover sites extremely thin. Horseshoe crab populations took a toll, and red knot population "numbers in Tierra del Fuego (winter) and Delaware bay (spring) declined about 75 percent from 1980s to 2000s". Male knots prepare 3–5 sites for nests on "normally dry, stony areas of tundra in upland areas, often near ridges and not far from wetlands". Thus, sea level rise, coastal erosion, and general warming temperatures due to global warming destroy the ideal breeding habitats for the red knot in these arctic coastal regions. Migratory animals by nature have adapted to various environments. Subsequently, rapid and complex responses to climate change are prominent and in the case of the red knot in the recent changing climate, evolutionarily damaging. As arctic breeding grounds continue to warm, red knot body size has decreased, and less success for survival of birds born in warmer years is reported. Even more significantly, their wintering areas in the tropics have become more stabilized, resulting in shorter bill birds (likely due to the fact that stable conditions breed greater ecological success and less variability within species). Consequently, knots struggle to reach their main food sources which include deeply buried molluscs, adding to lesser access to food as well as more expenditure of energy in attempting to attain food.

Late in the fall of 2014, the red knot rufa was listed as a federally threatened species under the United States Endangered Species Act – the second most critical status that can be awarded to a subspecies. This followed a decade of intensive petitioning by environmental groups and a lawsuit against the Department of the Interior for alleged negligence in the protection of endangered species through failure to evaluate and list them. The reasons for the red knot rufa's listing were varied; habitat degradation, loss of key food supplies, and threats posed by climate change and sea level rise were all listed as factors that were considered when the red knot rufa was listed.

  • (Red) Knot – Species text in The Atlas of Southern African Birds
  • Red knot Species Account – Cornell Lab of Ornithology
  • Red Knot – Calidris canutus – USGS Patuxent Bird Identification InfoCenter
  • Red Knot field guide at eNature.com
  • 2000 Arctic Search for the Red Knot – New Jersey Division of Fish and Wildlife
  • The Rufa Red Knot (Calidris canutus rufa) – US Fish and Wildlife Service
  • The Shorebird Project – an international team of biologists who monitor red knots and other shorebirds
  • Red Knot – An Imperiled Migratory Shorebird in New Jersey – New Jersey Division of Fish and Wildlife
  • RedKnot.org: Red Knots & Horseshoe Crabs – links to shorebird recovery sites, movies, events and other info on red knot rufa and horseshoe crabs.