The Red knot is a medium-sized shorebird that makes one of the longest yearly migrations of any bird. It's a bulky but very active bird with short dark legs and a medium thin dark bill. The winter or basic, plumage becomes uniformly pale grey and is similar between the sexes. The alternate, or breeding, plumage is mottled grey on top with a cinnamon face, throat and breast, and light-colored rear belly. The alternate plumage of females is similar to that of the male except it is slightly lighter and the eye-line is less distinct. The large size, white wing bar, and grey rump and tail make it easy to identify the Red knot in flight.
Red knots breed in the Arctic Cordillera in the far north of Canada, Europe, and Russia. North American breeders migrate to Europe and South America, while the Eurasian populations winter in Africa, Papua New Guinea, Australia, and New Zealand. Red knots breed in the moist tundra usually near water, streams or ponds, and often near the coasts. On the wintering grounds, these birds can be found in coastal areas, saltmarshes, estuaries, lagoons, bays, harbors, and sandy beaches.
Red knots are highly gregarious and form enormous flocks when not breeding. These are diurnal birds that spend most of their time wading in order to find food. While feeding in mudflats during the winter and migration Red knots are tactile feeders, probing for unseen prey in the mud. Their feeding techniques include the use of shallow probes into the mud while pacing along the shore. When the tide is ebbing, they tend to peck at the surface and in soft mud they may probe and plough forward with the bill inserted to about 1 cm (0.39 in) in depth. When foraging singly, Red knots rarely call, but when flying in a flock they make a low monosyllabic 'knutt' and when migrating they utter a disyllabic 'knuup-knuup'.
Red knots are carnivores. On the breeding grounds, they eat mostly spiders, arthropods, and larvae, and on the wintering and migratory grounds they eat a variety of hard-shelled prey such as mollusks, snails and small crabs; these are ingested whole and crushed by a muscular stomach.
Red knots are territorial and serially monogamous; they form pair bonds that remain together only for a single breeding season that occurs between June and August. Males arrive before females after migration and begin defending territories. As soon as males arrive, they begin displaying and aggressively defending their territory from other males. The courtship displays include circling high with quivering wing beats and tumbling to the ground with the wings held upward. During the display, the male performs a fluty 'poor-me' song. Red knot nest solitary on the ground, near water, and usually inland. The nest is a shallow scrape lined with leaves, lichens, and moss. Males construct 3 to 5 nest scrapes in their territories prior to the arrival of the females. The female lays 3 or 4 eggs that are ground colored, light olive to deep olive buff, with a slight gloss. Both parents incubate the eggs, sharing the duties equally. The off duty parent forages in flocks with others of the same species. The incubation period usually lasts around 22 days. The chicks are precocial (fully-developed) at hatching, covered in downy cryptic feathers. The young and the parents move away from the nest within a day of hatching and begin foraging with their parents. The female leaves before the chicks fledge while the male stays on. After the young have fledged, the male begins his migration south and the young make their first migration on their own. Fledgling occurs at 18-20 days old and maturity is generally reached by the 2 or 3 years of age.
In the late 19th century, large numbers of Red knots were hunted commercially for sport and food as they migrated through North America. At present important threats include habitat degradation, loss of key food supplies, and threats posed by climate change and sea-level rise. These birds also suffer from human disturbances, residential development, and recreational activities on their non-breeding grounds which destroy their foraging areas.
According to the IUCN Red List, the total Red knot population size is around 891,000-979,000 individuals. The European population consists of 15,000-30,000 pairs, which is around 30,000-60,000 mature individuals and the population overwintering in Australia and the Americas is around 110,000 individuals. Overall, currently, Red knots are classified as Near Threatened (NT) on the IUCN Red List and their numbers today are decreasing.