Bird Bio: Swainson’s Thrush

Bird Bio: Swainson’s Thrush
By: Robert Frey, KBO Biologist and Banding Project Leader

One of the most commonly heard, although seldom seen, birds of its range is the sedately plumed and melodic songster Swainson’s Thrush. It was named for William John Swainson, a much-accomplished English (and later in life a New Zealander) ornithologist, malacologist, entomologist, and artist. Mr. Swainson has had nine bird species named for him (Swainson’s Francolin, Hawk, Toucan, Fire-eye, Antcatcher, Flycatcher, Thrush, Warbler, and Sparrow).

The western-breeding Catharus ustulatus ustulatus group has a more russet color tone to its upperparts plumage. The boreal- and eastern-breeding C. u. swainsoni group is more brownish-olive. All have pale buffy “spectacles” and sing a wonderful ascending-note, flute-like song.

Swainson’s Thrushes nest across the boreal regions of North America, throughout much of the intermountain west, and along the Pacific Northwest coast.

They are associated with deciduous woodlands and riparian habitats in our region, specifically with a dense shrub layer; a habitat affinity shared by the Wrentit. They are also common in mixed conifer/deciduous forests. Western populations winter in Mexico, while boreal and eastern populations winter southward to Amazonia and further into Argentina’s southern lowlands – some traveler!

Although this species is numerous, with an estimated population of 100,000,000, there is evidence of Pacific Northwest populations declining since 1966. There is also evidence that the Swainson’s Thrush is particularly vulnerable to building strike mortalities, especially during migration.

Interestingly, the root word of Mr. Swainson’s family name, swain, is an Old English term for a male lover or admirer, or a country boy. We can’t say that this suits William John very well, but it may just be a wonderful occurrence of word evolutionary convergence for the sweet-singing son of
swain thrush!

This article can be seen in the Summer 2011 Newsletter.

Sources: Altman, B. 2000. Conservation strategy for landbirds in lowlands and valleys of western Oregon and Washington. PIF; Gruson, E. S. 1972. Words for birds: A lexicon of North American birds with biographical notes. Quadrangle Books, Inc., New York, New York; Marshall et al, eds. 2003. Birds of Oregon: A general reference. Oregon State University Press, Corvallis, Oregon; Rich et al. 2004. Partners in Flight North American Landbird Conservation Plan. Cornell Lab of Ornithology, Ithaca, New York.