Bird Lore: Swainson’s Thrush

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Swainson’s Thrush (Photos by Blair Bernson)
Swainson’s Thrush (Photos by Blair Bernson)

The Swainson’s Thrush is a herald of spring to many people. This neotropic migrant appears in Washington in May and departs by mid- to late-September. It can be found throughout Western Washington, from the Cascade Range to the Olympic Peninsula. This species also occupies the moister woods of mountainous regions in the northeast and southeast of the state.

The ventriloquist of the woods, the Swainson’s Thrush can be found in any of Edmonds’ forested parks. Its presence can be difficult to track because it moves quickly from one perch to another between songs. Its song may reverberate in dense foliage and it sometimes sings quietly, leaving the listener with the impression that the bird is farther away than it really is.

The Swainson’s Thrush eats mostly insects and berries. Insects include ants, beetles, caterpillars, crickets, flies, moths and wasps. The species will also feed on spiders and other invertebrates. Berries and other fruits can be up to one third of its summer diet. Its winter diet in the tropics is not well known but the species is often found there in fruiting trees. This thrush spends a lot of time feeding on the ground, although not as often as do some of the other brown thrushes. It also forages in trees where it may hover briefly to take insects from foliage. It also catches insects in midair.

Swainson's Thrush2 (BB)In spring the male arrives first on its breeding grounds, establishes a territory, and defends it with song. If an intruder enters its territory, it sleeks down its feathers and points its bill upwards. This is considered an aggressive defense display. The female builds her nest on a horizontal branch, usually 2-10 feet above ground. The Swainson’s Thrush often nests in conifers in the east and the north. In the west it often nests in deciduous trees or shrubs. The nest is a bulky, open cup of twigs, bark strips, and other vegetation, sometimes with added mud.

The female incubates her three to four eggs for about two weeks. Both parents feed the nestlings. The young birds leave the nest 10-13 days after hatching.

Conservation status of the Swainson’s Thrush is that of least concern. Nonetheless, it is a common species that has been declining across its range, by about 38 percent over the last 45 years. Because this species has a short breeding season, it is thought that Swainson’s Thrush may be sensitive to disturbance on nesting grounds, such as grazing, development and other human activity, as well as invasions of non-native plants. More so than for other migrating species, large numbers of Swainson’s Thrush die from collisions with tall buildings, windows, and radio and cell phone towers.

The oldest known Swainson’s Thrush was at least 12 years and one month of age when it was re-caught during banding operations in Montana.

You can hear the song of the Swainson’s Thrush here: http://www.xeno-canto.org/325253. Its “pit” and “rrehrr” calls can be heard here: http://www.xeno-canto.org/211332.

— By Carol Riddell

Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.

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