Systematics

Editor's Note: Analysis of mitochondrial and nuclear DNA sequences in members of the shorebird tribe Tringini suggests that the genus Catoptrophorus is embedded within Tringa and should be merged into it. Thus the 47th Supplement to the American Ornithologists' Union's Checklist of North American Birds now recognizes Willet as Tringa semipalmata. Future revisions of this account will reflect this change.

Two disjunct groups of breeding populations that differ in size (wing length, bill length and thickness, leg length, and body mass), plumage (especially Alternate plumage), vocalizations, breeding ecology, and to a large extent, winter ranges. These 2 groups are recognized as separate subspecies, C. s. semipalmatus and C. s. inornatus, referred to as Eastern and Western willet, respectively (see below). Both plumage and size appear to be more variable among Western Willets. For example, considerable variation in color, spotting, and barring within single breeding population in s. Alberta (CLG-T); wide variation in plumage pattern and size noted among large sample of Western Willet specimens at Academy of Natural Sciences in Philadelphia (K. Russell pers. comm.). No studies of genetic differences among populations.

Two subspecies recognized (Ridgway 1919, Am. Ornithol. Union 1957, Blake 1977). Reliable diagnosis requires measurements based on individuals of known age and sex. Identification to race in the field sometimes possible (see Wilds 1983, Hess 1998, and Sibley 2000). Western Willet larger sex for sex, although much overlap exists with Eastern Willet. Plumage differences most apparent in Alternate plumage, birds in Basic or Juvenal plumage differing more subtly.

Vocalizations differ, but of little use away from breeding areas. Vocalizations highly uniform among Eastern Willets across a broad geographic range (Douglas 1996). Western Willet vocalizations have not been studied as extensively, but duration of “ pill-will-willet,” or PWW, Call (see Sounds: vocalizations, below) significantly greater in 1 California population than in Utah populations that have been studied (Douglas 1996, Douglas and Conner 1999). Eastern and Western willets share same vocal repertoire, but “song” or self-advertisement call (i.e., PWW Call) of males differs statistically in both acoustical frequency and temporal characteristics (Douglas 1996). Eastern Willets discriminate between Eastern and Western songs, suggesting behaviorally facilitated reproductive isolation (Douglas 1998).

C. s. inornatus (Brewster, 1887) Western Willet: Breeds interior wetlands of Great Plains and Great Basin in w. North America; winters primarily along Pacific coast of North America south to s. South America (Chile) but also found along Atlantic Coast (Carolinas southward), Gulf coast, and more sparingly in Caribbean and coast of n. South America (e.g., Haverschmidt and Mees 1994); autumn migrants occur along coast of much of northeastern North America; casual to Alaska. Larger; wing length (chord) 193–220 mm, exposed culmen 54.3–65.0 mm (discrimination improved if age and sex known; see Appearance: measurements, below); bill relatively slender; generally paler, grayer than Eastern; Alternate plumage typically with relatively sparse spotting and barring, although some individuals may be heavily marked, with central rectrices varying from vaguely barred to fully barred to tail tip; Basic plumage with relatively pale whitish underparts and gray wash on breast often divided by white. Possible differences from nominate semipalmatus in wing pattern (breadth of white stripe) needs study.

C. s. semipalmatus (Gmelin, 1789) Eastern Willet: Breeds in coastal wetlands along Atlantic and Gulf coasts of North America and throughout much of West Indies; winters along Atlantic Coast of U.S. (as far north as Virginia but mostly south of there; e.g., Florida [Stevenson and Anderson 1994]), Gulf coast of the Caribbean, rarely Pacific coast of Middle America, and coastal Caribbean and Atlantic South America south to s. Brazil; casual in n. Manitoba, s. Ontario, s. Quebec, and Newfoundland; accidental to Bermuda and Europe. Smaller; wing length 174–200 mm, exposed culmen 50.0–59.0 mm (see Appearance: measurements, below); bill relatively more stout than inornatus; darker and browner overall, especially upperparts, being gray-brown above; Alternate plumage heavily marked with bars and spots and with tail usually prominently barred (but generally not reaching tail tip as on inornatus); Basic plumage browner than inornatus, with breast more solidly washed grayish brown.

Monotypic genus. Among sandpipers (Scolopacidae), Willet classified in subfamily Scolopacinae, tribe Tringini, along with genera Tringa, Heteroscelus, Actitis, and Xenus; sometimes all species of tribe Tringini merged into genus Tringa (Am. Ornithol. Union 1998; see also Chu 1995).