Birds
Swainson's Thrush
Catharus ustulatus · also called Swainsons thrush, olive-backed thrush
A thin, whistled note drifts down from the darkness overhead on a spring night, one voice among countless invisible migrants, evidence that a Swainson’s thrush is passing directly above, entirely hidden, on a journey conducted almost exclusively after sunset.
Overview
Swainson’s thrush, Catharus ustulatus, is a subtly patterned songbird native to coniferous and mixed forest habitat across much of Canada, Alaska, and mountainous parts of the western United States. Its upward-spiraling song, distinctive thin nocturnal flight call, and near-total commitment to migrating after dark make it one of the more acoustically and behaviourally distinctive thrushes passing through North America.
A song built as the mirror image of a relative’s
Where the closely related veery spirals its ethereal song downward, Swainson’s thrush does the exact opposite, climbing in pitch instead, a neat reversal between two close relatives that otherwise share a remarkably similar overall vocal quality.
Status
Least Concern overall, though gradually declining in parts of its range as forest habitat is lost on both its breeding grounds and its Central and South American wintering grounds.
Swainson's Thrush: common questions
How is Swainson's thrush's song different from the veery's?
Swainson's thrush produces an ethereal, flute-like song that spirals upward in pitch, while the closely related veery produces a similarly ethereal song that spirals downward instead, making the direction of the pitch spiral one of the clearest ways to distinguish the two species by ear even though both share a broadly similar overall song quality.
Why does Swainson's thrush migrate mostly at night?
Migrating at night likely offers several advantages, including cooler temperatures that reduce the energy cost of long flights, reduced predation risk from daytime hunting birds, and calmer atmospheric conditions in many regions, allowing this species to travel efficiently under cover of darkness while resting and feeding during the day.
What is the thin call heard overhead during migration at night?
This is Swainson's thrush's distinctive nocturnal flight call, a short, thin, whistled note that migrating birds produce while travelling overhead in darkness, a sound commonly picked up by birders and researchers using audio recording equipment specifically set up to monitor nighttime bird migration.
How can you identify a Swainson's thrush?
Look for a buff-coloured eye-ring and a subtly spotted breast on an overall olive-brown body, features that help distinguish it from closely related thrush species such as the veery and hermit thrush, which show different eye-ring colouration and overall body tone.