Systematics

Family Scolopacidae, subfamily Scolopacinae, tribe Calidridini (Am. Ornithol. Union 1998).

Subtle geographic variation in size and coloration, but with extensive overlap between subspecies (see below). Geographic studies of wing and bill length (see Table 1) and plumage variation (Roselaar 1983, Tomkovich 1990, Engelmoer and Roselaar 1998) argue that there are at least 5 subspecies (see below), which according to genetic studies (Baker et al. 1994), have geographically separated during the last 100,000 yr, some within the last 30,000 yr, with evidence of morphological change during the last 100 yr (Engelmoer and Roselaar 1998).

Five subspecies recognized, following Engelmoer and Roselaar 1998 and Roselaar 1983 . Divergence of Red Knot subspecies and other populations of shorebirds that breed north of the Jul 5° isotherm is thought to be the result of isolation in 3 cold re-fugia during the last glaciation (Larsen 1957). Gen-etic studies aimed at elucidating the phylogeography of Red Knot populations confirm that evolution of subspecies in knots was quite recent (Baker et al. 1994), albeit on a different scale from that envisioned by Larsen (1957). According to Larsen, refugia were in Europe and w. Asia, Beringia, and middle North America. A small area of n. Greenland also remained unglaciated. As glaciers receded, ranges of the differentiated knot subspecies expanded, in some cases to a degree where distributional boundaries today are unclear (e.g., C. c. rufa and C. c. islandica).

C. c. canutus (Linnaeus, 1758): Breeds in n.-central Siberia (centered around Taymyr Peninsula; Engelmoer and Roselaar 1998). Winters principally on w. African coasts of Mauritania and Guinea-Bissau. Small numbers, probably canutus, also winter in South Africa (Underhill and Summers 1992). Darkest subspecies; tends to have long bill and medium-length wings (Tomkovich 1992). Nominate canutus is entirely deep rufous below, including vent and under tail-coverts; black marks on upperparts heavy, rufous marks deeply colored but rather small, and rounded on tips of scapulars.

C. c. rufa (Wilson, 1813): Breeding range not known in detail; best summarized by Godfrey (1992). Breeding evidently centers in Canada north of Arctic Circle in northern district of Keewatin and in middle-arctic islands of southern district of Franklin, mostly west of 85° and east of 110°W. Confirmed breeding in 1999 and 2000 on Southampton I. Banding (Harrington and Leddy 1982, Harrington et al. 1988) shows that rufa spends boreal winter in s. South America, where Morrison and Ross (1989) found the species most abundant south of 40°S, especially in ne. Tierra del Fuego, but also numbering in low thousands near equatorial coastlines of Brazil (unclear whether these were rufa or roselaari, however; see below). Measurements overlap widely with canutus and islandica (Tomkovich 1992). C. c. rufa is palest subspecies, showing mainly white vent, lower flanks, and under tail-coverts, and hardly any rufous on upperparts; black marks above are restricted and narrow, upperparts appear silvery gray, rufous restricted to some on scapulars in male, hardly any in females; deep-rufous forehead, cheeks, foreneck, and chest contrast markedly with silvery crown, hindneck, and mantle (Tomkovich 1992). Baker et al. (1994) suggested that rufa and rogersi (see below) have become genetically separable within the last 30,000 yr—i.e., coinciding with the last two glaciations of the Pleistocene (Pielou 1991).

C. c. islandica (Linnaeus, 1767): Breeds in e. Canada on middle- and high-arctic islands principally east of 100°W, including the Queen Elizabeth Is. (Godfrey 1992). Also breeds on Ellesmere I. and in Greenland. Banding studies (Morrison 1975) show that islandica migrates from e. Canada and Greenland to Europe, where it winters principally on coasts of the United Kingdom and, to a lesser extent, other countries sharing coastlines of the North Sea, and the coast of France. Relatively short-billed and long-winged according to Roselaar (1983) when compared with rufa . Coloration close to nominate canutus, but rufous on underparts less intense, more yellowish on hindneck, and black marks above distinctly narrower; rufous on scapular tips shows as large, paired squarish dots. Formerly considered part of nominate canutus .

C. c. rogersi (Mathews, 1913): Breeds in New Siberian Is., Russia (Engelmoer and Roselaar 1998). Winters principally in Australasian region, especially New Zealand and Australia. Shorter bill and wings than rufa (Tomkovich 1992); appears less grayish and slightly more rufous above than rufa, with the dorsal black spots more prominent than in rufa, especially on mantle and scapulars (Roselaar 1983). Vent and lower belly light-colored as on rufa, but often marked with black. Formerly considered part of nominate canutus .

C. c. roselaari Tomkovich, 1990: Breeding range not well known, but in North America probably centers on Alaska’s Seward Peninsula (R. Gill pers. comm.), possibly extending westward to Chukchi Peninsula and Wrangel I., Russia. Wintering zones poorly known, but may include small numbers on Pacific Coasts of U.S. and Mexico (Roselaar 1983, Tomkovich 1990), west coast of Florida (Harrington et al. 1988), Texas coast (BAH), and possibly small numbers on tropical Atlantic coasts of South America north of the Equator (see Morrison and Ross 1989). Roselaar (1983) and Tomkovich (1990) suggested that most roselaari winter on west coasts of North, Central, and South America. Longer-winged than the other races, but bill length overlaps extensively. Alternate plumage dorsal coloration is similar to that of nominate canutus, but darker with slightly more variegated pattern; ventral coloration more similar to that of rufa than to that of rogersi, especially with respect to amount of white plumage on vent and lower belly (Tomkovich 1990, 1992).

Molecular genetics study using mitochondrial DNA indicates that knots are one of the oldest lineages in the clade of calidridine sandpipers, having diverged from approximately 4.6–6.1 million years ago (Baker 1992); on the basis of genetic dis-tances, they are among the most divergent of those species sampled within genus Calidris . Red and Great knots are thought to be a species pair resulting from isolation in the Tertiary (Larsen 1957). The downy young of knots (see Appearance, below) have “powder puff” characteristics, considered primitive by Fjeldså (1977), suggesting knots as transitional between Surfbirds (Aphriza virgata) and more typical calidrines.

Hybridization

None reported.