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.
| 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) |
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)
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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)
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