Swainson's Thrush

The Swainson's thrush, known scientifically as Catharus ustulatus, is a medium-sized thrush with a modest yet pleasing appearance. It is a member of the genus Catharus, characterized by its understated coloration and enchanting, ascending flute-like voice. Named in honor of the English ornithologist William Swainson, this bird is also referred to as the olive-backed thrush and russet-backed thrush due to the coloration of its plumage.

Identification Tips

Adult Swainson's thrushes exhibit a brown upper body, with eastern birds showing more olive-brown hues and western birds displaying a reddish-brown tint. The underparts are white, with brown flanks and a lighter brown breast adorned with darker spots. They possess pink legs and a subtle brown eye ring. Notably, they feature the white-dark-white underwing pattern typical of Catharus thrushes. The species measures 16–20 cm in length, with a wingspan averaging 30 cm, and weighs between 23 to 45 grams.

Habitat

The preferred breeding habitat of Swainson's thrush is coniferous woods with dense undergrowth, spanning across Canada, Alaska, and the northern United States. They are also found in deciduous wooded areas along the Pacific coast of North America.

Distribution

Swainson's thrushes undertake a remarkable migration to wintering grounds in southern Mexico and as far south as Argentina. Coastal subspecies migrate along the Pacific coast, wintering from Mexico to Costa Rica, while continental birds take a detour eastwards within North America before heading south via Florida to winter from Panama to Bolivia. This species is an occasional rare vagrant to western Europe and northeast Asia.

Behaviour

Swainson's thrushes forage on the forest floor and in trees. They are known to be displaced by hermit thrushes where their ranges overlap, possibly due to the latter's better adaptation to human encroachment. In their winter quarters, they tend to avoid areas with human activity and construction.

Song & Calls

The song of the Swainson's thrush is a series of hurried, flute-like tones that spiral upwards, creating a melodious and distinctive sound that enchants listeners in their natural habitat.

Diet and Feeding

These thrushes primarily feed on insects, fruits, and berries. They exhibit a preference for the fruits of Cymbopetalum mayanum and Trophis racemosa in their winter quarters, although they generally avoid feeders or disturbed habitats.

Breeding

Swainson's thrushes construct a cup-shaped nest on a horizontal tree branch, where they lay their eggs and raise their young.

Similar Species

While similar in appearance to other Catharus thrushes, the Swainson's thrush can be distinguished by its unique song and underwing pattern.

Conservation status

The Swainson's thrush is currently listed as Least Concern by the IUCN, indicating that it is not at immediate risk of widespread decline.

Subspecies

There are four recognized subspecies of Swainson's thrush: C. u. almae, C. u. swainsoni, C. u. ustulatus, and C. u. oedicus. These subspecies are divided into two genetically distinct clades, the coastal and continental, which diverged approximately 10,000 years ago. The subspecies differ in their migratory routes and summering locations, with some favoring east and others west of certain mountain ranges in North America.