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COSEWIC Assessment and Status Report on the Red Knot in Canada

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COSEWIC
Executive Summary

Red Knot
Calidris Canutus

rufa subspecies (Calidris canutus rufa)
roselaari type (Calidris canutus roselaari type)
islandica subspecies (Calidris canutus islandica)

Species Information

The Red Knot (Calidris canutus) is a medium-sized shorebird with a typical “sandpiper” profile: long bill and smallish head, long tapered wings giving the body an elongated streamlined profile, and longish legs. In breeding plumage, knots are highly distinctive, with face, neck, breast and much of the underparts coloured a rufous chestnut red. Feathers on the upperparts are dark brown or black with rufous and grey, giving the back a spangled appearance. In winter plumage, knots are much plainer, with white underparts and pale grey back. Six subspecies are currently recognized worldwide, all of which form distinct biogeographical populations differing in distribution and scheduling of the annual cycle. Subspecies occurring in Canada include C. c. rufa, C. c. roselaari, and C. c. islandica.

Distribution

C. c. rufa breeds in the central Canadian Arctic and winters in Tierra del Fuego at the southern tip of South America. C. c. roselaari, which for the purposes of this report is divided into three subpopulations, includes a Pacific population that winters in California and northwest Mexico and breeds in northern Alaska, passing through western Canada on migration, and two populations wintering in Florida/SE US and Maranhão, Brazil, respectively, that likely breed in central and western parts of the Canadian Arctic. The Florida and Maranhão populations clearly form separate biogeographic populations from the Pacific roselaari and the southern South American rufa populations; their taxonomic status is currently under revision. C. c. islandica breeds in the northeastern Canadian High Arctic (and in Greenland) and winters in areas on the European seaboard.

Habitat

In the Arctic, knots nest on barren habitats such as windswept ridges, slopes, or plateaus, often with less than 5% vegetation. On migration and wintering areas, knots use coastal areas with extensive sandflats (sometimes mudflats), where the birds feed on bivalves and other invertebrates. They are also known to use peat banks, salt marshes, brackish lagoons, mangrove areas, mussel beds, and in South America, restingas, which are rocky intertidal platforms with a rich invertebrate fauna.

Biology

Knots are monogamous, with pairs usually laying a single clutch of four eggs, in the latter half of June, with the eggs hatching around mid-July. Females depart soon thereafter, leaving the males to accompany the young until they can fly. Breeding success varies considerably from year to year, depending on weather and the abundance of predators, which itself varies over a 3-4 year cycle depending on the abundance of lemmings.

Population Sizes and Trends

The current population size for C. c. rufa is 13 500 – 15 000 adult birds based on counts from the wintering areas in Tierra del Fuego and Patagonia. Surveys from the wintering grounds suggest that the population has decreased by 70% since 1982. Numbers at the major wintering sites in Tierra del Fuego remained fairly steady until 2000, but have since declined dramatically. Few knots now remain at “peripheral” sites along the coast of Patagonia, which held significant numbers in the 1980s. Similar declines have been observed throughout the migration range of rufa, confirming an actual population decline rather than a redistribution of the birds to different areas.

The current population size for C. c. roselaari knots wintering in Florida/SE US is approximately 3375 adult birds. This group has declined by about 70% in the last 15 years. Less information is available for the Maranhão population, which may have declined by about 7% over the past 20 years to about 5700 adults. Available evidence suggests the Pacific population of roselaari has also declined by about 60% in the last 15-20 years, with a current population size of 1500-3000 adults. The overall decline for the combined population is 47%.

Current C. c. islandica populations wintering in Europe now number about 202 500 adults. This represents a decline of about 17% since the late 1990s.

Limiting Factors and Threats

The single most important threat to rufa and roselaari knots wintering in Florida/SE US and Maranhão, Brazil has been the overfishing of horseshoe crabs (Limulus polyphemus) in Delaware Bay, leading to a decimation in numbers of horseshoe crab eggs, the most important food used during the final spring stopover. Degradation of habitats in areas such as San Francisco Bay and Grays Harbor, WA has likely affected the Pacific coast populations of roselaari, while overfishing of shellfish on major wintering areas in the Dutch Wadden Sea have affected C. c. islandica wintering in Europe.

Other possible threats include decreased habitat availability during migration in eastern North America (providing few alternative sites for the birds to use), disturbance, increased risk from severe weather events (e.g., hurricanes) during migration, oil and chemical pollution in North and South America, climate change effects including sea level rise and changing conditions on the Arctic breeding grounds, and increased levels of predation from rebounding predator (e.g., falcon) populations.

Special Significance of the Species

Red Knots have long been regarded as a “flagship” species for shorebird conservation, because of their enormously long, inter-continental migrations and their vulnerability owing to concentration in large numbers (involving a large proportion of the population) at a limited number of key sites. Philosophically, they are a wildlife species shared by many nations, crossing many international boundaries, and are symbolic of the need for international cooperation for their successful conservation. Conservation of sites used by knots will also benefit many other shorebird species.

Existing Protection

Red Knots are protected under the Migratory Birds Convention Act (1917, updated in 1994). A formal status assessment in the US resulted in their being listed as a “candidate species,” indicating they qualified for endangered species status. Knots are listed as Threatened in New Jersey and as of Special Concern in Georgia. They have been added to Appendix I of the Convention on Migratory Species (“Bonn” Convention), which lists species threatened with extinction. NatureServe lists the rufa subspecies of Red Knots globally as G4T1, or critically imperiled globally at the subspecies level: national status is N1N, or critically imperiled in its non-breeding range in the US, and N1B and N1N, or critically imperiled in both breeding and non-breeding range in Canada.