Swainson's Thrush - Catharus ustulatus

Swainson's Thrush has a partial preformative molt but no prealternate molts. Age can usually be determined reliably through examination of the primary and greater coverts, but some intermediates may become more difficult to identify by spring and should be considered M-FCF (AHY) unless multiple characteristics indicate a particular age. Sex can generally be determined only by brood patch / cloacal protuberance during the breeding season.

Swainson's Thrush can generally be distinguished from the other Catharus thrushes by its buffy eye ring and cheek, and its uniformaly olive-brown back and tail, but beware the potential for confusion with western populations of Veery that have quite similar upperparts.

Quick tips

• Look at the greater coverts - on FCF (HY/SY) birds, up to a few innermost ones (often two) are generally longer and uniform in colour, while the remainder are retained juvenile feathers and often show buffy-white shaft streaks, although these may be less evident by spring; the absence of such streaks should therefore not be used as evidence of DCB (AHY/ASY).
• Examine the short outermost primary (p10) - on FCF (HY/SY) birds it is broad, rounded, and similar in length to the primary coverts (1 mm longer to 6 mm shorter), while on DCB (AHY/ASY) birds it is narrow, pointed, and 4-9 mm shorter than the primary coverts.
• Consider the shape of the rectrices - they are narrow and relatively pointed on FCF (HY/SY) birds, but broad and relatively rounded on DCB (AHY/ASY) birds.

Species account prepared by McGill Bird Observatory (2016). Last updated by Marcel Gahbauer (Mar 2022)