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Swainson's Thrush Life History


ForestsSwainson’s Thrushes breed mainly in coniferous forests, except in coastal California where they are found primarily in deciduous streamside woodlands, alder or willow thickets, and occasionally in coastal scrub. These birds range from sea level up to about 8,500 feet in elevation. In coastal California, where their habitat may depend on the presence of fog, they tend to stay below about 500 feet. During migration, Swainson’s Thrushes occupy a wide variety of habitats, seeking mainly areas with dense undergrowth. Look for migrants especially in forests, canyon bottoms, young woodland, swamp forests, lake edges, and parks. Winter habitat includes primary and old second-growth tropical forest and forest-pasture edges.Back to top


InsectsSwainson’s Thrushes eat largely insects and arthropods during the breeding season; they also eat fruits, particularly in fall and winter. They tend to reject yellow fruits and favor red ones, going after elderberries, blackberries, raspberries, twinberries, huckleberries, and other wild fruits including those of brier, false Solomon’s seal, and sumac. Insect prey items include beetles, caterpillars, flies, grasshoppers, and bugs. Swainson’s Thrushes also feed on ants—a dietary item more commonly associated with some woodpeckers and unusual among temperate songbirds. Nestlings are fed mostly insects, including especially caterpillars, beetles, moths, and flies.Back to top


Nest Placement

ShrubSwainson’s Thrushes nest in shady sites in the forest understory—especially in thickets of deciduous shrubs or conifer saplings, mostly 3–10 feet off the ground. They build their nests on plants such as willow, fir, spruce, blackberry, alder, aspen, birch, maple, oak, briers, gooseberry, rose, and sumac.

Nest Description

The nest is a compact, open cup, 1.5-4 inches high, with outside and inside diameters of about 3.5-6 inches and 2-3.3 inches respectively and a depth of 1.0-2.5 inches. It’s constructed of fine twigs, stems, grass, moss, bark shreds, and decayed leaves, and lined inside with skeletonized leaves, rootlets, lichens, or moss. The female builds the nest by herself over a period of about four days. Like other thrushes, she probably shapes the nest by snuggling low into the cup and thrusting with breast and feet. She builds a new nest each season.

Nesting Facts

Clutch Size:1-5 eggs
Egg Length:0.8-1.0 in (2-2.6 cm)
Egg Width:0.6-0.7 in (1.5-1.8 cm)
Incubation Period:10-14 days
Nestling Period:10-14 days
Egg Description:Blue to greenish blue speckled with reddish or brown.
Condition at Hatching:Blind, partially covered with natal down, eyes closed.
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Foliage GleanerSwainson’s Thrushes feed at higher levels than their relatives. They move in short hops along branches looking for food, gleaning from leaves of broad-leaved and coniferous trees. Going after insects, they also lunge, hover, and flycatch. Swainson’s Thrushes often perch on low twigs or branches to survey the litter below, then dive for prey. On the forest floor, they take long, springy hops from one hunting stop to the next. In addition to the male’s haunting song, a peeping flight call, and other vocalizations, Swainson’s Thrushes communicate aggression and other attitudes with a variety of silent body poses and displays, such as wing-flitting, leaf-tossing, and foot-quivering. On migration stopovers, Swainson’s Thrushes may join multispecies foraging flocks. On breeding grounds, mating begins with the male chasing a fleeing female. As the courtship warms up, the pair progresses to slow flights and perching together.Back to top


Low Concern

Swainson’s Thrush is a common species whose population held fairly steady between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 120 million and rates them 10 out of 20 on the Continental Concern Score. This species' short breeding season may render it sensitive to disturbance on nesting grounds. Problems on breeding grounds include grazing, development, human activity, and the invasion of nonnative plants. During spring and fall migration, significant numbers of Swainson’s Thrushes die from collisions with windows, radio and cell-phone towers, and tall buildings. (For more on the dangers of lights to migrating birds, visit the Fatal Light Awareness Program.) Studies of bird deaths at communications towers in Minnesota, Illinois, and West Virginia revealed that Swainson’s Thrushes were killed in greater numbers than any other bird species.

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Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Mack, Diane Evans and Wang Yong. (2000). Swainson's Thrush (Catharus ustulatus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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