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Catharus ustulatus (Nuttall, 1840)
Swainson's Thrush
Family: Turdidae

Species account author: Jamie Fenneman

Distribution of Catharus ustulatus in British Columbia.
(Click on the map to view a larger version.)

Source: Distribution map provided by Jamie Fenneman for E-Fauna BC

Adult
Back, scapulars, rump, upperwings, and tail rich olive-brown reddish-brown with a slightly stronger reddish tinge on the tail (‘Russet-backed’ subspecies group) or duller olive-brown and often tinged with grey (’Olive-backed’ subspecies group). The underparts are whitish to creamy-white, usually with a buffy wash across the breast, with variable brown to almost blackish spots across the breast and a brownish to olive-grey wash on the sides and flanks. There is a broad buffy stripe across the base of the flight feathers on the underwing that is visible in flight. The head is dull olive-brown to richer reddish-brown (depending on subspecies group), with buffy lores and a buff eye ring that create the impression of pale ‘spectacles’. The ear coverts are finely streaked with buff, and the throat is buff to buffy white. The malar area is buffy, with the buff colour extending around the rear edge of the ear coverts, and there is a line dark spots along the lower edge of the malar area (usually appearing as a dark malar stripe). The iris is dark, the short, slender, pointed bill is black with a flesh-coloured base to the lower mandible, and the legs and feet are flesh-pink.

First-winter immature
This plumage is acquired in late summer and is retained through fall migration. It is very similar to the plumage of the adults, but is distinguished by the small buffy tips to the greater upperwing coverts that form a relatively inconspicuous pale wing bar.

Juvenile
Birds retain this plumage into the late summer of their first year, but molt prior to fall migration. It is generally similar to the plumage of the adult, but the head, upperparts, and upperwing coverts are finely but heavily spotted and streaked with buff and the underparts have heavier and more extensive dark spotting (extending onto the belly).

Measurements
Total Length: 17-17.5 cm
Mass: 25.5-38 g

Source: Mack and Yong (2000); Sibley (2000)

Manitoba Museum of Man and Nature's Glossary of Ornithology Terms

Identification

The identification of Catharus thrushes in North America can be relatively complicated, particularly given the tendency for many members of this genus to be secretive and skulky during migration, rarely affording reasonable views. There are several characteristics, however, that should allow the Swainson’s Thrush to be differentiated from other species in B.C. if seen well.

Throughout its distribution in the province, this species overlaps in range with the Hermit Thrush. Hermit Thrush tends to be less skulky than Swainson’s Thrush, often foraging out in the open on lawns and other open areas (Swainson’s Thrush is much more closely tied to dense thickets). When on the ground, the Hermit Thrush characteristically cocks its tail up and regularly flicks its wings; both of these behaviours are absent or infrequent in Swainson’s Thrush and can assist with identification. When seen well, the relatively brighter, redder tail and uppertail coverts of Hermit Thrush that contrast noticeably with the browner upperparts is a good mark for identification, although some coastal Swainson’s Thrushes can show a slightly redder tail and care should be used in that region. In addition, Hermit Thrush has heavier and blacker spotting on the throat and underparts, particularly when compared to coastal Swainson’s Thrushes, and lacks the bold buffy ‘spectacles’ of Swainson’s Thrush (although it does have buffy lores and a thin whitish eye ring). The typical call note of Hermit Thrush (a low, dry chup) is very different from the liquid puip of Swainson’s Thrush.

In southern B.C. and some areas of central B.C., Swainson’s Thrush occurs alongside the Veery and can sometimes be difficult to distinguish from that species. Many observers can be led astray by the relatively heavy-spotted western subspecies of Veery that is found in B.C. and is very different from the almost unspotted eastern subspecies; western Veeries are much more similar to Swainson’s Thrush (especially ‘Russet-backed’ coastal birds) than eastern individuals. The Veery is nonetheless considerably brighter and more rufous-toned than even the brightest Swainson’s Thrushes, with reduced and browner (less blackish) spotting on the breast and a plainer face pattern with almost no eye ring (although the lores are still buffy). The underparts of the Veery are also cleaner and whiter than Swainson’s Thrush, with a paler and less extensive brown or olive wash on the sides and flanks.

In northern B.C., the Gray-cheeked Thrush breeds at elevations above Swainson’s Thrush, but there is some overlap and the two species overlap widely in elevation during migration. Gray-cheeked Thrush is noticeably colder grey-brown on the head and upperparts, and has a strong grey wash to the ear coverts. As well, it lacks the buffy ‘spectacles’ that are so prominent on Swainson’s Thrush and therefore has a much plainer, greyer face pattern. Immature Gray-cheeked Thrushes are slightly brighter than adults, but still have this plainer, greyer face pattern. Additionally, the breast of the Gray-cheeked Thrush is more heavily spotted than any other Catharus thrush in North America, including Swainson’s Thrush.

Vocalizations

The familiar and beautiful song of coastal birds (‘Russet-backed’ subspecies group) is a spiraling, ascending series of fluid, slurred, flute-like notes preceded by several short whistled notes: po po tu tu tu tureel tureel tiree tree tree. The song of interior birds (‘Olive-backed’ subspecies group) is similar, but the spiraling, ascending, slurred phrases are composed of only a single syllable, and there is usually only one introductory note (sometimes no introductory note): po rer reer reeer re-e-e-e-e-e. Calls include a low, liquid puip or quip and a rough, nasal, braying or laughing chatter that is usually preceded by a single note qui-brrrrrr. Also gives a clear, level, emphatic heep or queev flight call, especially during migration. ‘Russet-backed’ birds along the coast give a burry, descending vreeew that is not given by interior ‘Olive-backed’ birds.

Source: Mack and Yong (2000); Sibley (2000)

Bird calls (and videos) from Cornell's Lab of Ornithology

Breeding Ecology

Courtship
Males arrive on the breeding grounds earlier than females and defend territories from nearby males. Pair bonds form immediately after the arrival of females, coinciding with the peak in song activity of the male. The male often engages in courtship chases during the formation of pair bonds.

Nest
Nest building begins 2-3 weeks after arrival on the breeding grounds, with most nest-building occurring in B.C. in late May or the first half of June. The female constructs the nest alone over a period of ~4 days. The nest is generally situated within a low shrub, small deciduous tree, or in the dense boughs of a conifer sapling, although some nests are placed at mid levels in the forest understory or even within the canopy; nest heights range from ground level to 24 m, with most nests at heights of 1-2.5 m. The nest is generally placed near the trunk and is usually well hidden by surrounding vegetation. The nest is placed atop a horizontal branch or lodged in the fork or crotch of a branch, although some nests are placed on the ground among tree roots. The nest itself is a compact cup (9.5-15.5 cm across and 4.0-10.5 cm deep) of grasses, plant stems, leaves, moss, strips of bark, rootlets, mud, and small twigs and is lined with skeletonized leaves, rootlets, lichens, and moss.

Eggs
A clutch of (1) 3-4 (5) eggs is laid in late May or during the first half of June and is incubated for 10-14 days by the female before hatching. This species is double-brooded along the southern coast of the province, and in this region a second clutch is sometimes laid in July. The smooth, glossy eggs are pale blue to greenish-blue with variable amounts of reddish-brown to purplish-brown or pale lilac speckles, spots, and blotches; the markings are often concentrated toward the larger end of the egg, although some eggs are uniformly marked (often quite densely). Eggs occur in B.C. between late May and early August. This species is a relatively infrequent host for Brown-headed Cowbird nest parasitism, although parasitism is widespread in B.C.

Young
The young are fully altricial and downy with dark brown down; the mouth is orange and the gape flanges are pale yellow. The nestling period is 10-14 days, during which time the young are fed and tended by both parents until fledging (brooded only by female). The period of parental care following fledging is unknown, but based on other thrush species may be ~20-30 days, after which time the young become fully independent. Nestlings and dependent fledglings have been observed in B.C. between mid-June and late August (most between late June and mid-July).

Source: Baicich and Harrison (1997); Campbell et al. (1997); Mack and Yong (2000)

Foraging Ecology

This species feeds on adult and larval insects and berries throughout the year, although breeding birds and spring migrants consume a greater proportion of insects while fall migrants consume more berries and small fruits. In coastal B.C., this species consumes large amounts of salmonberries during the breeding season in June, often competing with American Robins for the same berry crop. The few winter records for B.C. have primarily been of birds foraging for berries along with flocks of American Robins. Most foraging activity takes place on the ground or in shrubs and low levels of trees, although this species is more likely to ascend into the canopy to forage than other Catharus thrushes. Most food is captured by picking and gleaning from the foliage and twigs or from the ground, although it will also pursue aerial insects in short flights (does this more frequently than other Catharus thrushes). It commonly perches in low foliage and scans the ground for prey, then descends to the ground to capture the prey.

Source: Mack and Yong (2000)

The Swainson’s Thrush breeds in a wide variety of forested habitats, particularly pure coniferous forests and mixed woodlands, and is particularly abundant in young second-growth stands with a dense understory of shrubs. It is found at low to moderate (sometimes high) elevations across southern parts of the province, but is primarily confined to low elevations farther north. This species occurs commonly in coastal forests of Western Redcedar, Western Hemlock, Sitka Spruce, Douglas-fir, Red Alder, and Bigleaf Maple as well as in mixed forests of Douglas-fir, Lodgepole Pine, spruce, Subalpine Fir, Paper Birch, and Trembling Aspen in the interior. In drier regions of the interior, it also breeds in deciduous stands with scattered coniferous trees as well as riparian stands of Black Cottonwood, but is otherwise uncommon in pure deciduous woodlands. Migrants occur in similar forested habitats as well as riparian thickets, upland brushy areas, aspen copses, and residential parks and gardens. The presence of dense shrubs appears to be an important habitat component for this species throughout the year.

Source: Campbell et al. (1997); Mack and Yong (2000)

Global Range

Widespread breeder across northern portions of North America, from Alaska east to Newfoundland and south to the Great Lakes and northern Appalachians. It is also common and widespread throughout western Canada and the United States, south to southern California, Arizona, and New Mexico. It winters from central and southern Mexico south to central South America.

BC Distribution

Breeding
Fairly common to common breeder throughout all of British Columbia, including Vancouver Island, the Queen Charlotte Islands, and all other coastal islands.

Migration
The Swainson’s Thrush is a relatively late spring migrant in B.C., the first migrants usually not appearing until early to mid-May (rarely late April) across southern portions of the province; earlier records (some as early as March) largely refer to misidentified Hermit Thrushes. Peak movements on the south coast and across the southern interior are in late May, while peak movements farther north are in early June. Fall migration begins in late July or early August, and numbers slowly decline throughout the month of August in all areas of the province. Although almost all birds have vacated northern parts of the province by late August, southward migration continues across southern B.C. through the first half of September, with occasional individuals lingering into late September or early October (latest on the south coast).

Casual on the south coast in November and December, and accidental in the southern interior (Shuswap Lake) in December. There are very few winter records of this species anywhere in North America.

Population and Conservation Status

This species is a common breeder throughout all of British Columbia, and is not recognized as a species of conservation concern by either COSEWIC (Committee on the Status of Endangered Wildlife in Canada) or the B.C. CDC (Conservation Data Centre).

Six subspecies of Swainson’s Thrush are recognized, which fall into two distinct, discrete groups that differ in plumage, voice, habitat choice, and distribution and may represent separate species. See ‘Vocalizations’ for notes on differences in songs and calls between these two subspecies groups. Both subspecies groups are found in B.C., with coastal breeders representing the ‘Russet-backed’ or ustulatus group and interior breeders representing the ‘Olive-backed’ or swainsoni group.

The four subspecies that occur in British Columbia are as follows:

Catharus ustulatus ustulatus
The most common and widespread member of the ‘Russet-backed’ subspecies group. This subspecies breeds along the Pacific coast of North America from southeast Alaska to coastal California and winters in Mexico and northern Central America. The head, wings, tail, and upperparts of this subspecies are olive-brown with a distinct rufous or reddish tinge (brightest on the tail, which contrasts slightly with the browner back and wings). The underparts are less heavily spotted than members of the ‘Olive-backed’ group, and have a brownish wash on the sides and flanks (olive wash in ‘Olive-backed’ group).

Catharus ustulatus phillipsi Ramos
This is a member of the ‘Russet-backed’ subspecies group. It breeds only on the Queen Charlotte Islands and winters in Mexico. It is very similar to C.u.ustulatus, but is brighter reddish-brown on the head, wings, tail, and upperparts and is even more lightly-spotted on the breast.

Catharus ustulatus swainsoni (Tschudi)
This is the most widespread member of the ‘Olive-backed’ subspecies group. It breeds from the central and southern interior of British Columbia east throughout the boreal forest to the Atlantic Ocean and winters from Mexico south to northern South America. It differs from ustulatus and other members of the ‘Russet-backed’ subspecies group in its olive-brown head, wings, tail, and upperparts with no contrast between the colour of the tail and the colour of the back. The dark spotting on the underparts is heavier and darker, and there is an olive (rather than brownish) wash on the sides and flanks.

Catharus ustulatus incanus (Godfrey)
This is a member of the ‘Olive-backed’ subspecies group. It breeds in Alaska, the Yukon, northern British Columbia, and northern Alberta and winters in South America. It is similar to C.u.swainsoni but is noticeably greyer on the head, wings, and upperparts and has a slightly brighter, rufous-tinged tail that contrasts with the colour of the back. The buffy areas of the face (lores, eye ring, throat) are paler than swainsoni and the underparts are slightly greyer and have darker and heavier blackish spotting on the breast.

Source: Campbell et al. (1997); Mack and Yong (2000); Sibley (2000)

Origin Status	Provincial Status	BC List (Red Blue List)	COSEWIC
Native	S5B	Yellow	Not Listed

BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Washington Dept. of Fish and Wildlife Predictive Range Maps
Avibase -- the World Bird Database
Birdpedia

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