Grayer overall than most of its North American relatives, Swainson’s Thrush (7 inches) is most easily separated from a similar species, the Gray-cheeked Thrush, by its buff-brown cheeks and conspicuous eye-rings. Other field marks include a spotted breast, pink legs, and a medium-length bill. Male and female Swainson’s Thrushes are similar to one another in all seasons. The Swainson’s Thrush breeds in Alaska and across a wide swath of central and southern Canada. Smaller numbers are found south of the Canadian border, particularly along the Pacific coast and at higher elevations in the Appalachians and the Rocky Mountains. Swainson’s Thrush winters in southern Mexico and Central America south to Argentina. In summer, Swainson’s Thrush breeds primarily in evergreen forests dominated by spruce and fir trees. During the winter, this species inhabits wet tropical forests. On migration, Swainson’s Thrush may be found in a variety of habitats with dense undergrowth available for foraging and cover. Many North American birders never travel far south enough to see Swainson’s Thrush in winter. This species is much easier to observe in summer and on migration, although it is more often heard than seen due to its preference for habitats with thick vegetation. Swainson’s Thrush may be observed foraging food while hopping along the forest floor or through the branches of trees. Swainson’s Thrush is most active during the day, but, like many migratory songbirds, this species migrates at night.
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Breeding
Regularity: Regularly occurring
Type of Residency: Breeding
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Nesting range extends from western and central Alaska across all of Canada (north to north-central Yukon, southern Northwest Territories (Great Bear Lake), northern Manitoba, nnorthern Ontario, north-central Quebec to about 54°N, central Labrador, and northern Newfoundland), and south through Pacific coast states to southern California, south through the Rocky Mountains to Arizona and northern New Mexico, south in the Great Plains and Great Lakes regions to eastern Montana, Black Hills of South Dakota, southern Saskatchewan, and northern Minnesota, and south in eastern North America to northern Pennsylvania, New England, and disjunctly to Virginia (Mack and Yong 2000). Range during the northern winter is mainly in Mexico and northern South America (east of the Andes in Colombia, Venezuela, Ecuador, eastern Peru, northern and eastern Bolivia, and northwestern Argentina, with a few records from western Amazonian Brazil and coastal southwestern Peru) (Ridgely and Tudor 1989); also occurs in smaller numbers in Central America (Mack and Yong 2000).
Length: 18 cm
Weight: 31 grams
Habitat and Ecology
Comments: Breeding habitat includes dense vegetation in coniferous forests, mixed hardwood-conifer forests (e.g., across Canada and northern New England, predominantly hardwood forests (e.g., in Northeast), riparian woodland and thickets of willow or alder (e.g., California and other western states at south end of range), aspen forests (e.g. southwest part of range), and sometimes coastal scrub (California) (Mack and Yong 2000). Depending on the location, this species may be associated with young, mature, or old growth (see Mack and Wong 2000). Range-wide, nesting occurs at elevations from sea level to 2,600 meters or higher. Nests usually are in small trees, close to the trunk, often 2 meters or less above ground; often in conifers, sometimes deciduous trees or shrubs (e.g., willow).
During migration, this species uses a wide range of wooded and shrubby habitats, generally with thick undergrowth.
During the boreal winter, Swainson's thrushes inhabit a wide range of conditions that may vary with region, including primary forest, mature selva forest, tropical semideciduous forest, humid to semihumid evergreen and semideciduous forest (including pine-oak, coniferous, tropical deciduous, and cloud forest), secondary growth, and forest-pasture edges, and human-made openings with ornamental shrubs (see Mack and Yong 2000).
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Abundant migrant in Costa Rica, mid-September to November and April-late May (Stiles and Skutch 1989). Most common migrant thrush in Colombia; transient and winter resident in South America early October-late April (Hilty and Brown 1986).
Comments: Eats insects and other invertebrates, small fruits, seeds (Terres 1980). Very frugivorous in migration and during northern winter, sometimes concentrates in large numbers near fruiting trees and shrubs (Hilty and Brown 1986). In Costa Rica, eats many fruits and arillate seeds, relatively few insects and other invertebrates; may forage along edge of army ant swarms (Stiles and Skutch 1989).
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: > 300
Comments: This species is represented by a large number of occurrences (subpopulations).
Comments: Total adult population size is unknown but certainly exceeds 1,000,000. Rich et al. (2004) estimated population size at 100,000,000.
Nonbreeding: solitary or in loose flocks in migration (Stiles and Skutch 1989, Rappole and Warner 1980).
Life History and Behavior
Comments: May sing day and night in Alaska.
Lifespan, longevity, and ageing
Clutch size usually is 3-4. Incubation, by female, lasts 10-14 days. Young are tended by both parents, leave nest at 10-14 days.
Molecular Biology and Genetics
Barcode data: Catharus ustulatus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Catharus ustulatus
Public Records: 31
Specimens with Barcodes: 44
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5B - Secure
Rounded National Status Rank: N5B - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Wide nesting range in North America; numerous subpopulations; large population size; slow rate of decline over the past several decades; major threat is habitat loss, degradation, and fragmentation in breeding range and winter range.
Global Short Term Trend: Relatively stable (=10% change)
Comments: Breeding Bird Survey (BBS) data for 1980-2007 indicate a range-wide statistically significant decline of 0.8% per year, primarily reflecting a decline in Canada (no significant trend in the United States). Time frame for short-term trend (three generations) is roughly 18 years; over that period BBS data indicate very little change in abundance (number of birds per route).
Global Long Term Trend: Increase of 10-25% to decline of 30%
Comments: Declines in distribution have been noted in California (see Mack and Yong 2000) and Massachusetts (Veit and Petersen 1993).
This species appears to have undergone a slow long-term decline. Breeding Bird Survey (BBS) data for 1966-2007 indicate a range-wide statistically significant decline of 0.6% per year. The same rate of decline applies to both the United States and Canada, but the trend is significant only for Canada.
Degree of Threat: Medium
Comments: Primary threat is habitat loss, degradation, and fragmentation affecting portions of the breeding range and wintering range (see review by Mack and Yong 2000).
Global Protection: Very many (>40) occurrences appropriately protected and managed
Swainson's thrush (Catharus ustulatus), also called olive-backed thrush, is a medium-sized thrush. It is a member of Catharus genus and is typical of it in terms of its subdued coloration and beautiful voice. Swainson's thrush was named after William Swainson, an English ornithologist.
The breeding habitat of Swainson's thrush is coniferous woods with dense undergrowth across Canada, Alaska, and the northern United States; also, deciduous wooded areas on the Pacific coast of North America.
These birds migrate to southern Mexico and as far south as Argentina. The coastal subspecies migrate down the Pacific coast of North America and winter from Mexico to Costa Rica, whereas the continental birds migrate eastwards within North America (a substantial detour) and then travel southwards via Florida to winter from Panama to Bolivia. Swainson's thrush is a very rare vagrant to western Europe. It has also occurred as a vagrant in northeast Asia.
This species may be displaced by the hermit thrush where their ranges overlap. Possibly, the latter species adapts more readily to human encroachment upon its habitat. At least in the winter quarters, Swainson's thrush tends to keep away from areas of human construction and other activity.
This species is 16–20 cm (6.3–7.9 in) in length. The wingspan averages at 30 cm (12 in) and the wing chord is 8.7–10.5 cm (3.4–4.1 in). The bill measures 1.5–1.9 cm (0.59–0.75 in) in length and the tarsus is 2.5 to 3.1 cm (0.98 to 1.22 in) long. This species' body mass can range from 23 to 45 g (0.81 to 1.59 oz). This thrush has the white-dark-white underwing pattern characteristic of Catharus thrushes. Adults are brown on the upperparts. The underparts are white with brown on the flanks; the breast is lighter brown with darker spots. They have pink legs and a light brown eye ring. Birds in the east are more olive-brown on the upperparts; western birds are more reddish-brown. This bird's song is a hurried series of flute-like tones spiralling upwards.
They forage on the forest floor, also in trees. Swainson's thrushes mainly eat insects, fruits and berries. They make a cup nest on a horizontal tree branch.
Four subspecies are recognised, Cathartus ustulatus alame, C. u. swainsoni, C. u. ustulatus and C. u. oedicus. Subspecies Cathartus ustulatus alame and C. u. swainsoni summer east of the British Columbian Coast Mountains, the Cascades and the Sierra Nevada, and C. u. ustulatus and C. u. oedicus summer west of these ranges. There is a small area of overlap in the Coast Mountains. Recent molecular systematics work confirms that these two pairs of subspecies form two genetically distinct clades, referred to as the continental and coastal clades, which diverged during the Late Pleistocene era, probably about 10,000 years ago as the last ice age came to its end and habitats shifted across North America.
The genetic differences between the subspecies, and the circuitous migratory route of the continental birds, strongly suggest that these species underwent a rapid range expansion following the end of the last ice age, with populations originally summering in the south-east of North America expanding their ranges northwards and westwards as the ice retreated. Details of the molecular genetic analysis support the hypothesis of rapid expansion of both coastal and continental populations. The current migratory routes of the continental birds, especially the western populations, are not optimal in ecological terms, and presumably represent an inherited, historical route pattern that has not yet adapted to the birds' modern population locations.
These results notwithstanding, analysis of mtDNA cytochrome b and NADH dehydrogenase subunit 2 as well as nuclear β-fibrinogen intron 7 sequence data shows that Swainson's thrush is the most ancient North American species of its genus; it is not closely related to other Catharus and the outward similarities with the other North American species are due to convergent evolution.
- BirdLife International (2012). "Catharus ustulatus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- Brazil, Mark (2009) Birds of East Asia ISBN 978-0-7136-7040-0 page 402
- Thrushes by Peter Clement. Princeton University Press (2001), ISBN 978-0-691-08852-5
- Out of the wide range of fruit eaten by this bird, those of Cymbopetalum mayanum (Annonaceae) and especially Trophis racemosa (Moraceae) are well-liked whenever available in the winter quarters. However, they are generally not taken from feeders or disturbed habitat: Foster (2007)
- Ruegg & Smith (2002)
- Winker & Pruett (2006)
- Foster, Mercedes S. (2007): The potential of fruiting trees to enhance converted habitats for migrating birds in southern Mexico. Bird Conservation International 17(1): 45-61. doi:10.1017/S0959270906000554 PDF fulltext
- Ruegg, K. C., & Smith, T.B. (2002). Not as the crow flies: a historical explanation for circuitous migration in Swainson's thrush (Catharus ustulatus). Proc. R. Soc. B 269(1498) 1375-1381. doi:10.1098/rspb.2002.2032 PDF fulltext
- Winker, Kevin & Pruett, Christin L. (2006): Seasonal migration, speciation, and morphological convergence in the avian genus Catharus (Turdidae). Auk 123(4): 1052-1068. [Article in English with Spanish abstract] DOI: 10.1642/0004-8038(2006)123[1052:SMSAMC]2.0.CO;2 PDF fulltext
Names and Taxonomy
Comments: Formerly placed in genus HYLOCICHLA (AOU 1983). Composed of two groups: SWAINSONI (Olive-backed Thrush) and USTULATUS (Russet-backed Thrush) (AOU 1998).