- North-West Atlantic Ocean species (NWARMS)
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Breeding
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Nesting range in North America is in northwestern and northern Alaska, and Canadian arctic islands east to Ellesmere and south to southern Victoria and Southhampton islands, probably also on Adelaide Peninsula and Mansel Island; nesting also occurs in the northern Palearctic.
During the boreal winter, the range in the New World extends mainly from coastal regions of southern California, Gulf Coast and Massachusetts south to Tierra del Fuego; generally rare north of southern South America; major South American nonbreeding areas are Tierra del Fuego and Patagonian coast of Argentina, especially Bahia Lomas (Morrison and Ross 1989). New World red knots principally occupy two areas: about 100,000 birds along Atlantic coast of southern Argentina, about 10,000 along Florida Gulf Coast, with no evidence of interchange between the 2 groups (Harrington et al. 1988). In the Old World, most red knots are in southern Europe, southern Asia, Africa, and the Australasian region during the boreal winter.
Nonbreeders occasionally summer in the winter range.
Delaware Bay is the most important spring migration stopover in the eastern United States (Clark et al. 1993, Botton et al. 1994).
Length: 27 cm
Weight: 148 grams
- Urban, E.K., C.H. Fry & S. Keith (1986). The Birds of Africa, Volume II. Academic Press, London.
Habitat and Ecology
Comments: Primarily seacoasts on tidal flats and beaches, less frequently in marshes and flooded fields (AOU 1983). On sandy or pebbly beaches, especially at river mouths; feeds on mudflats, loafs and sleeps on salinas and salt-pond dikes (Costa Rica, Stiles and Skutch 1989). Nests on ground in barren or stony tundra and in well-vegetated moist tundra.
Water temperature and chemistry ranges based on 14 samples.
Depth range (m): 0 - 0
Temperature range (°C): 9.226 - 13.104
Nitrate (umol/L): 1.865 - 7.963
Salinity (PPS): 32.515 - 35.399
Oxygen (ml/l): 6.089 - 6.688
Phosphate (umol/l): 0.256 - 0.562
Silicate (umol/l): 1.647 - 4.330
Temperature range (°C): 9.226 - 13.104
Nitrate (umol/L): 1.865 - 7.963
Salinity (PPS): 32.515 - 35.399
Oxygen (ml/l): 6.089 - 6.688
Phosphate (umol/l): 0.256 - 0.562
Silicate (umol/l): 1.647 - 4.330
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Red knots migrate long distances between nesting areas in mid- and high arctic latitudes and southern nonbreeding habitats as far north as the coastal United States (low numbers) and southward to southern South America, and to southern Asia, Africa, and Australasian region. Subspecies rufa migrates from nesting areas in the central Canadian Arctic to wintering grounds at the southern tip of South America.. Subspecies islandica breeds in the northeastern Canadian High Arctic and Greenland and migrates to wintering areas in Europe. Subspecies roselaari breeds in Alaska and on Wrangel Island and is thought to comprise the population wintering in Florida and on coastlines of the Gulf of Mexico, the Caribbean, and northern South America (Piersma and Davidson 1992, Harrington 2001).
Red knots migrate in large flocks northward through the contiguous United States mainly April-June, southward July-October (Bent 1927). Arrival in breeding areas occurs in late May or early June; most have departed breeding areas by mid-August. The species is more abundant in migration along the U.S. Atlantic coast than on the Pacific coast. Knots that visit Delaware Bay in spring come mostly from South America, and these have strong fidelity to migration stopover sites; those that winter in Florida are underrepresented during migration in New Jersey and Massachusetts. Migration through Costa Rica occurs late August-October and mainly mid-March to late April (Stiles and Skutch 1989). This species typically makes long flights between stops (Hayman et al. 1986). See Piersma and Davidson (1992) for information on knot migration.
Comments: Eats mainly mollusks, eggs of crab and horseshoe crab, insects, some seeds and small fishes; pecks and snatches at sand or mud, or probes. Horseshoe crab eggs are an important source of food for north-bound migrants at Delaware Bay (Botton et al. 1994).
Comments: Global population estimated to be 1,291,000 individuals (Rose and Scott 1997); North American portion is thought to be on the order of 400,000 (Morrison et al. 2001).
See also information for subspecies rufa.
Nonbreeding: usually in compact flocks.
Life History and Behavior
Comments: See Robert et al. (1989).
Lifespan, longevity, and ageing
Lays clutch of usually 4 eggs, June-July. Incubation lasts about 20-25 days, by both sexes. Young are tended mostly by male (female leaves before fledging), leave nest soon after hatching, can fly at about 18 days (Terres 1980).
Molecular Biology and Genetics
Barcode data: Calidris canutus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
-- end --
Download FASTA File
Statistics of barcoding coverage: Calidris canutus
Public Records: 9
Specimens with Barcodes: 27
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N3B - Vulnerable
Rounded National Status Rank: N3N,N4B : N3N: Vulnerable - Nonbreeding, N4B: Apparently Secure - Breeding
NatureServe Conservation Status
Rounded Global Status Rank: G4 - Apparently Secure
Status in Egypt
Regular passage visitor.
Global Short Term Trend: Relatively stable to decline of 30%
Global Long Term Trend: Relatively stable to decline of 50%
Comments: Population trend estimates at Delaware Bay and eastern Canadian migration stopover sites for subspecies rufa have been consistently negative over the past several decades, though some of the decline data were not statistically significant (Howe et al. 1989, Clark et al. 1993, Morrison et al. 1994, Morrison, Aubry et al. 2001).
Recent population surveys showed a dramatic decline of the population that winters primarily in South America (main wintering areas on the coasts of Patagonia and Tierra del Fuego, Argentina and Chile, corresponding with subspecies rufa, which comprises a portion of the North American nesting population) (González et al. 2004, Morrison et al. 2004). Totals in 2003 were about 30,000 compared to 67,500 in the mid-1980s. Numbers at the principal wintering site, Bahia Lomas, fell by approximately 50%, from 45,300 in 2000 to 22,000-25,000 in 2002-2003. Numbers at peripheral sites on the coast of Patagonia declined dramatically, decreasing 98% compared to numbers in the mid-1980s. The declines at core sites did not result from a shift of birds within the known wintering (or other) areas, but reflected a general population decline, with most birds now restricted to key sites in Tierra del Fuego (Morrison et al. 2004). These data do not include red knot populations that nest: (1) in the northeastern Canadian arctic (i.e., Queen Elizabeth Islands, Ellesmere Island) or Greenland, which winter in the Old World (C. c. islandica), (2) in northwestern Alaska and Wrangel Island (subspecies roselaari; winter range poorly documented, may include the Pacific coasts of North, Central, and South America, the northern tropical Atlantic coast of South America, the Texas coast, and Florida), or (3) in the Palearctic.
Subspecies roselaari breeds in Alaska and is presumed to include those knots that winter on the Pacific coast of the U.S. and Mexico (Niles et al. 2007). Two other red knot wintering populations of uncertain subspecific status exist in the Western Hemisphere: one in the southeastern United States (about 7,000 birds) and one on the north coast of Brazil (about 7,500 birds); these populations apparently have not suffered the same catastrophic decline as has occurred in the rufa population that winters in Tierra del Fuego (Niles et al. 2007).
Calidris c. islandica populations increased from the late 1970s until 2000; steep decrease since 2000 (Delany and Scott 2002).
Use of Massachusetts Bay as a migration stop evidently has declined from the historical situation (Harrington 2001).
Degree of Threat: High
Comments: Increased commercial harvest of horseshoe crabs (for use as bait in eel and conch fisheries; especially in the Delaware Bay region in the 1990s; Walls et al. 2002, Morrison et al. 2004), a reduction in horseshoe crab populations, and a consequent reduction in red knot food resources (horseshoe crab eggs), body condition during spring migration, and annual survival (Baker et al. 2004) are major concerns for population that migrate along the U.S. Atlantic coast (González et al. 2006, Niles et al. 2007).
Actions to conserve horseshoe crabs have included reduced harvest quotas, more efficient use of crabs as bait, closure of the harvest in certain seasons and places, and the designation of a sanctuary off the mouth of Delaware Bay (Niles et al. 2007). The latest information is that the crab population may have stabilized, but there is no evidence of recovery (Niles et al. 2007).
Relevance to Humans and Ecosystems
Stewardship Overview: See information for subspecies rufa.
The red knot (Calidris canutus) (just knot in Europe) 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. Six subspecies are recognised.
Their diet varies according to season; arthropods and larvae are the preferred food items at the breeding grounds, while various hard-shelled molluscs are consumed at other feeding sites at other times. North American breeders migrate to coastal areas in Europe and South America, while the Eurasian populations winter in Africa, Papua New Guinea, Australia, and New Zealand. This species forms enormous flocks when not breeding.
Taxonomy, systematics, and evolution
This Red Knot was first described by Linnaeus in the landmark 1758 tenth edition of his Systema Naturae as Tringa canutus. One theory is that it gets its name and species epithet from King Canute, Knot being another form of Canute; the name would refer to the knot's foraging along the tide line and the story of Canute and the tide. Another etymology is that the name is onomatopoeic, based on the bird's grunting call note.
|Population relatedness and divergence|
The diversification events may be associated with the Wisconsinan (Weichselian) glaciation 18,000 to 22,000 years ago; the opening of the ice-free corridor in North America 12,000 to 14,000 years ago; and the Holocene climatic optimum 7,000 to 9,000 years ago.
The red knot and the great knot were originally the only two species placed in the genus Calidris, but many other species of sandpiper were subsequently added. A 2004 study found that the genus was polyphyletic and that the closest relative of the two knot species is the surfbird (currently Aphriza virgata).
- C. c. roselaari – (Tomkovich, 1990) – (largest)
- C. c. rufa – (Wilson, 1813)
- C. c. canutus – (Linnaeus, 1758)
- C. c. islandica – (Linnaeus, 1767)
- C. c. rogersi – (Mathews, 1913)
- C. c. piersmai – (Tomkovich, 2001) – (smallest)
Studies based on mitochondrial sequence divergence and models of paleoclimatic changes during the glacial cycles suggest that canutus is the most basal population, separating about 20,000 years ago (95% confidence interval: 60,000–4,000 years ago) with two distinct lineages of the American and Siberian breeders emerging about 12,000 years ago (with a 95% confidence interval: 45,000–3,500 years ago).
Distribution and migration
In the breeding season, the red knot has a circumpolar distribution in the high Arctic, then migrates to coasts around the world from 50° N to 58° S. The red knot has one of the longest migrations of any bird. Every year it travels more than 9,000 mi (14,000 km) from the Arctic to the southern tip of South America. The exact migration routes and wintering grounds of individual subspecies are still somewhat uncertain. The nominate race C. c. canutus breeds in the Taymyr Peninsula and possibly Yakutia and migrates to the Western Europe and then down to western and southern Africa. C. c. rogersi breeds in the Chukchi Peninsula in eastern Siberia, and winters in eastern Australia and New Zealand. Small and declining numbers of rogersi (but possibly of the later described piersmai) winter in the mudflats in the Gulf of Mannar and on the eastern coast of India. The recently split race C. c. piersmai breeds in the New Siberian Islands and winters in north-western Australia. C. c. roselaari breeds in Wrangel Island in Siberia and north-western Alaska, and it apparently winters in Florida, Panama and Venezuela. C. c. rufa breeds in the Canadian low Arctic, and winters South America, and C. c. islandica breeds in the Canadian high Arctic as well as Greenland, and winters in Western Europe.
Birds wintering in west Africa were found to restrict their daily foraging to a range of just 2–16 km2 (0.77–6.18 sq mi) of intertidal area and roosted a single site for several months. In temperate regions such as the Wadden Sea they have been found to change roost sites each week and their feeding range may be as much as 800 km2 (310 sq mi) during the course of a week.
B95, also known as Moonbird, is a noted individual of the subspecies C. c. rufa. A male, he has become famous amongst conservationists for his extreme longevity — he was aged at least 20 as of his last sighting in May 2014.
Description and anatomy
An adult red knot is the second largest Calidris sandpiper, measuring 23–26 cm (9.1–10.2 in) long with a 47–53 cm (19–21 in) wingspan. The body shape is typical for the genus, with a small head and eyes, a short neck and a slightly tapering bill that is no longer than its head. It has 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-coloured 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. Canutus, islandica and piersmai are the "darker" subspecies. Subspecies rogersi has a lighter belly than either roselaari or piersmai, and rufa is the lightest in overall plumage. The transition from alternate to basic plumages begins at the breeding site but is most pronounced during the southwards migration. The molt to alternate plumage begins just prior to the northwards migration to the breeding grounds, but is mostly during the migration period.
The large size, white wing bar and grey rump and tail make it easy to identify in flight. When feeding the short dark green legs give it a characteristic 'low-slung' appearance. When foraging singly, they rarely call, but when flying in a flock they make a low monosyllabic knutt and when migrating they utter a disyllabic knuup-knuup. They breed in the moist tundra during June to August. The display song of the male is a fluty poor-me. The display includes circling high with quivering wing beats and tumbling to the ground with the wings held upward. Both sexes incubate the eggs, but the female leaves parental care to the male once the eggs have hatched.
Juvenile birds have distinctive submarginal lines and brown coverts during the first year. In the breeding season the males can be separated with difficulty (<80% accuracy in comparison to molecular methods) based on the more even shade of the red underparts that extend towards the rear of the belly.
The weight varies with subspecies, but ranges between 100 and 200 g (3.5 and 7.1 oz). Red knots can double their weight prior to migration. Like many migratory birds they also reduce the size of their digestive organs prior to migration. The extent of the atrophy is not as pronounced as species like the bar-tailed godwit, probably because there are more opportunities to feed during migration for the red knot. Red knots are also able to change the size of their digestive organs seasonally. The size of the gizzard increases in thickness when feeding on harder foods on the wintering ground and decreases in size while feeding on softer foods in the breeding grounds. These changes can be very rapid, occurring in as little as six days.
Diet and feeding
On the breeding grounds, knots eat mostly spiders, arthropods, and larvae obtained by surface pecking, and on the wintering and migratory grounds they eat a variety of hard-shelled prey such as bivalves, gastropods and small crabs that are ingested whole and crushed by a muscular stomach.
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. The bivalved mollusc Macoma is their preferred prey on European coasts, swallowing them whole and breaking them up in their gizzard. In Delaware Bay, they feed in large numbers on the eggs of horseshoe crabs which spawn just as the birds arrive in mid-summer. 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. Unlike many tactile feeders their visual field is not panoramic (allowing for an almost 360 degree field of view), as during the short breeding season they switch to being visual hunters of mobile, unconcealed prey, which are obtained by pecking. Pecking is also used to obtain some surface foods in the wintering and migratory feeding grounds, such as the eggs of horseshoe crabs.
The red knot is territorial and seasonally monogamous; it is unknown if pairs remain together from season to season. Males and females breeding in Russia have been shown to exhibit site fidelity towards their breeding locales from year to year, but there is no evidence as to whether they exhibit territorial fidelity. 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 red knot nests on the ground, near water, and usually inland. The nest is a shallow scrape lined with leaves, lichens and moss. Males construct three to five nest scrapes in their territories prior to the arrival of the females. The female lays three or more usually four eggs, apparently laid over the course of six days. The eggs measure 43 mm × 30 mm (1.7 in × 1.2 in) in size and are ground coloured, 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 lasting around 22 days. At early stages of incubation the adults are easily flushed from the nest by the presence of humans near the nest, and may not return for several hours after being flushed. However in later stages of incubation they will stay fast on the eggs. Hatching of the clutch is usually synchronised. The chicks are precocial at hatching, covered in downy cryptic feathers. The chicks and the parents move away from the nest within a day of hatching and begin foraging with their parents. The female leaves before the young fledge while the males stay on. After the young have fledged, the male begins his migration south and the young make their first migration on their own.
The red knot has an extensive range, estimated at 100,000–1,000,000 km2 (39,000–386,000 sq mi), and a large population of about 1.1 million individuals. The species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations), and is therefore evaluated as Least Concern. However many local declines have been noted such as the dredging of intertidal flats for edible cockles (Cerastoderma edule) which led to reductions in the wintering of islandica in the Dutch Wadden Sea. The quality of food at migratory stopover sites is a critical factor in their migration strategy.
This is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. This commits signatories to regulate the taking of listed species or their eggs, to establish protected areas to conserve habitats for the listed species, to regulate hunting and to monitor the populations of the birds concerned.
Threats to the subspecies rufa
Towards the end of the 19th century, large numbers of red knot were shot for food as they migrated through North America. It is hypothesized that more recently, the birds have become threatened as a result of commercial harvesting of horseshoe crabs in the Delaware Bay which began in the early 1990s. Delaware Bay is a critical stopover point during spring migration; the birds refuel by eating the eggs laid by these crabs (with little else to eat in the Delaware Bay). If horseshoe crab abundance in the Bay is reduced there may fewer eggs to feed on which could negatively affect knot survival.
In 2003, scientists projected that at its current rate of decline the American subspecies, rufa, might become extinct as early as 2010, but as of April 2011 the subspecies is still extant. In New Jersey, state and local agencies are taking steps to protect these birds by limiting horseshoe crab harvesting and restricting beach access. In Delaware, a two-year ban on the harvesting of horseshoe crabs was enacted but struck down by a judge who cited insufficient evidence to justify the potential disruption to the fishing industry but a male-only harvest has been in place in recent years.
Threatened Status of rufa
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 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.
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