Systematics

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In the past, genus Calidris was on occasion reserved for present species and C. tenuirostris only.

Body size, bill length (see Table 1), dorsal pattern and color, and ventral color and extent vary in a complex and subtle manner across the Holarctic breeding range of this species (Roselaar 1983, Tomkovich 1990, 1992, 2001, Engelmoer and Roselaar 1998). Breeders in the high Arctic and nw. Russia are wholly reddish below, whereas breeders in the low Arctic and e. Siberia have white through the vent and undertail coverts. Populations in the low Arctic of Canada are grayest above and palest below, whereas those across n. Russia are blackest above and deepest rufous below. In general breeders at more southerly latitudes are smaller than more northerly breeders, although the smallest population is on the New Siberian archipelago with the largest on Wrangel I. and in nearby nw. Alaska.

Six subspecies—following Tomkovich (1992) and Engelmoer and Roselaar (1998), as amended by Tomkovich and Serra (1999) and Tomkovich (2001)—differentiated by the depth and extent of reddish color on the ventrum, darkness of markings on the dorsum, and bill length and body size. Diagnoses below are for individuals in full Alternate (breeding) plumage. Genetic studies suggest that these six allopatric subspecies arose since the last glacial maximum ~20,000 yr ago (95% CI 60,000–4000 ya), with evidence of morphological evolution during the past 100 yr (Engelmoer and Roselaar 1998). About 12,000 yr ago two lineages diverged, one leading to North American breeders and the other to strictly Siberian breeders. Divergence times of these two Siberian subspecies are ~6500 yr ago, and populations of the North American breeding subspecies are estimated to have diverged within the past ~1000 yr. These divergence times suggest that all ancestral populations of knots emerged within the last glacial period of the Pleistocene via an eastward expansion into North America (Buehler and Baker 2005). Races islandica, rogersi and, until recently, roselaari formerly included within nominate canutus.

C. c. canutus (Linnaeus, 1758). Includes Tringa cinerea Brünnich, 1764, and T. calidris Linnaeus, 1766. Breeds in nw. Russia, from the Taimyr Peninsula east to Cape Chekyuskin; winters in w. and s. Africa [type locality = Sweden]. Ventrum uniformly deep rufous; nape reddish gray; on dorsum, black marks heavy but rufous marks small and rounded on scapular tips; bill long and wings intermediate in length (Tomkovich 1992).

C. c. islandica (Linnaeus, 1767). Includes Tringa naevia Gmelin, 1789; T. grisea Gmelin, 1789; and Canutus rufescens Brehm, 1855. Breeds in the high latitudes of Arctic Canada and on Greenland and Svalbard; winters in w. Europe and around the Mediterranean [type locality = Iceland]. Like C. c. canutus, but nape and ventrum paler and yellower (Tomkovich 1992), black marks on dorsum narrower, and rufous marks on scapular tip squared; bill averages shorter but wing averages longer (Roselaar 1983).

C. c. rufa (Wilson, 1813). Breeds in the low latitudes of Arctic Canada; winters from the Gulf of Mexico south to e. South America [type locality = New Jersey]. Like C. c. canutus, but lower flanks, vent, and undertail coverts white, ventral color paler (more soft chestnut, less deep rufous), nape grayish, and black marks on dorsum restricted with rufous marks there nearly absent (imparting a silvery gray appearance).

C. c. rogersi (Mathews, 1913). Includes Tringa lomatina Lichtenstein, 1854. Breeds on the Chukotka Peninsula, Siberia (Tomkovich and Serra 1999); winters in e. Australia and New Zealand [type locality = Shanghai, China]. Similar to C. c. rufa, but dorsum less gray and more rufous with black marks more prominent, nape pale gray (nearly whitish), and ventrum paler (more peach-chestnut) and often marked with black; both the bill and wing average shorter (Tomkovich 1992).

C. c. roselaari Tomkovich, 1990. Breeds on Wrangel I., Siberia, and in nw. Alaska [type locality = Mamontovaya River valley, Wrangel I.]; winters on the Pacific Coast from s. California south to Central America (see Patten et al. 2003). Similar to C. c. canutus dorsally (perhaps slightly darker) and ventrally (but averages less uniform reddish); the largest and longest-billed subspecies, on average (Tomkovich 1990, 1992, Tomkovich and Dondua 2008).

C. c. piersmai Tomkovich, 2001. Breeds in the New Siberian archipelago [type locality = Bolshoy Lyakhovsky Island]; winters in nw. Australia. Similar to C. c. roselaari, but ventrum brick-red, nape reddish, and dorsum heavily marked with black and rufous (Tomkovich 2001, Rogers et al. 2010); the smallest and shortest-billed subspecies, on average.

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SUBSPECIES

Calidris canutus canutus Scientific name definitions

Distribution

CN Siberia, in Taymyr Peninsula and possibly Yakutia; winters in W and S Africa and S Asia.

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SUBSPECIES

Calidris canutus piersmai Scientific name definitions

Distribution

New Siberian Is; winters in NW Australia.

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SUBSPECIES

Calidris canutus rogersi Scientific name definitions

Distribution

Chukotskiy Peninsula and possibly areas farther W; winters in Australasia.

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SUBSPECIES

Calidris canutus roselaari Scientific name definitions

Distribution

Wrangel I (off NE Siberia) and NW Alaska; probably winters on coasts of SE USA (Florida), S Panama and N Venezuela.

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SUBSPECIES

Calidris canutus rufa Scientific name definitions

Distribution

Canadian low Arctic; winters on coasts of NE and S South America.

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SUBSPECIES

Calidris canutus islandica Scientific name definitions

Distribution

islands of Canadian high Arctic and N Greenland; winters in W Europe.

The sandpipers, family Scolopacidae, are a key component of the speciose avian order Charadriiformes (van Tuinen et al. 2004), and genus Calidris is a key component of the sandpiper family. Monophyly of the genus Calidris is disputed routinely, with arguments for some monotypic genera, such as Aphriza (the Surfbird) and Eurynorhynchus (the Spoon-billed Sandpiper), being merged into Calidris (e.g., Jehl 1968, Burton 1971) as well as arguments for other divergent species being in monotypic genera. Molecular phylogenetics suggest that C. canutus is sister to Calidris virgata—they diverged from a common ancestor 11–22 mya (Baker et al. 2007)—rather than to C. tenuirostris, the Great Knot, a species superficially similar in structure. Still, these three species constitute a clade that is the most divergent lineage among the calidridine sandpipers, attesting to this group's antiquity within the Scolopaci (Gibson and Baker 2012).

• Red Knot x Surfbird (hybrid) Calidris canutus x virgata

No information.