This species is the most common migrant Catharus in much of North America. Polytypic (2 ssp. groups: olive-backed and russet-backed). Length 7".
Typically bold, buffy eye ring and supraloral patch of most Swainson’s thrushes distinctive. Adult: in “olive-backed” group, upperparts olive-brown with slightly more reddish uppertail coverts. Strong, usually dark brown, lateral throat stripes contrast with buffy throat and malar stripes; ear surround usually buffy and obvious, but varies in distinctness and color. Chest spots dark brown and round, often somewhat pointed on top, and usually entirely within buffy wash. Sides and flanks olive-gray. Tail similar in color to upperparts in eastern subspecies, more reddish in western races, often contrasting slightly with upperparts. Typically lacks contrasting wing panel. Bill dull yellow, with dark culmen and tip, not contrasting with face color. Juvenile: spotted buff above, dark gray-brown below, with white throat; some older immatures distinguishable by presence of retained juvenal wing coverts with buffy shaft streak.
Six subspecies, some of questionable validity; subspecific identification in field problematic due to slight differences and individual variation. Olive-backed group: widespread swainsoni described; appalachiensis upperparts slightly darker and same color as uppertail coverts; incanus of western Alaska to northern British Columbia and north-central Alberta has upperparts paler and grayer, underparts whiter, and chest spotting nearly black. Russet-backed group: Northwestern coastal ustulatus (southeastern Alaska to northwestern California) and phillipsi (Queen Charlotte Islands) upperparts brown, tinged reddish, with breast washed brownish with indistinct spots, and flanks warm brown; and oedicus of rest of California paler brown above with almost no reddish tinge; eye rings of western subspecies usually thinner, sometimes less buffy.
Russet-backed subspecies is regularly confused with western salicicola Veery, but note differences in breast spotting, flank color, and facial pattern.
Call: russet-backed gives a liquid dwip, olive-backed a sharper quirt; also a rough, nasal chatter introduced by call note. Flight note: clear, spring peeper-like queep. Song: flutelike, similar to Veery in spiraling pattern, but spiraling upward.
Status and Distribution
Common, but in West restricted by limited suitable habitat. Breeding: mostly in deciduous and/or mixed forest; birds in western U.S. primarily nest in riparian habitat with combination of shrubby willow understory and deciduous or coniferous overstory. Migration: olive-backed group are trans-Gulf migrants; russet-backed birds migrate along Pacific coast and California deserts. Peaks on Gulf Coast ±25 April, southern Great Lakes ±15 May; arrival in montane Wyoming breeding areas ±25 May; spring migration continues into early June as far south as Kansas. In fall, most migrate September–mid-October, arrival on Colorado plains ±25 August. Russet-backed winters from western Mexico to Panama; olive-backed birds winter in South America. Vagrant: casual to accidental to northern Alaska and Northwest Territories; casual to Europe.
Like other brown thrushes, forest fragmentation may negatively impact populations.
—From the National Geographic book Complete Birds of North America, 2006