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Range
 Breeds
from western and central Alaska, central Yukon, and western
and southern Mackenzie across the Prairie provinces north of
the grasslands, and east into Labrador and Newfoundland; in
the west, south to southern California; in the east, to
southern New York, New Hampshire, and West Virginia. Winters
primarily from southern Mexico south to Brazil, Peru, and
Argentina.
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Status
On the coast, a fairly common
to common migrant and summer visitant in the Georgia
Depression Ecoprovince; uncommon to fairly common on Western
Vancouver Island, the mainland coast, and the Queen
Charlotte Islands of the Coast and Mountains Ecoprovince.
Casual in winter in the Georgia Depression.
In the interior, a fairly
common to common migrant and summer visitant in the Southern
Interior and Southern Interior Mountains ecoprovinces,
becoming uncommon to fairly common further north. Accidental
in winter in the Southern Interior.
Breeds.
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Status
Change
No change.
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Nonbreeding
 The
Swainson's Thrush is widely distributed throughout the
province, including offshore islands. Information is lacking
regarding this thrush's occurrence in the mountainous areas
of the Southern Mainland Coast, the western Chilcotin
Plateau, the Blackwater region, the lower Nechako and
McGregor river basins, and the Rocky Mountain Trench
northward between Mackenzie and Lower Post.
While some of these gaps may
reflect the lack of suitable habitat, others suggest the
need for further biological exploration.
In migration along the coast,
the Swainson's Thrush has been reported from sea level to
about 800 m elevation. In the southern portions of the
interior, it usually occupies elevations between 450 and
1,200 m; further north the species is rarely found above 800
m.
 Since
the Swainson's Thrush is a characteristic summer bird in
much of the province, there is considerable overlap between
the wide variety of habitats it occupies during the
nonbreeding and breeding periods. In the Coast and
Mountains, it is most numerous along marine and freshwater
shorelines where dense thickets of salal, salmonberry, or
devil's club produce a supply of fruit close to the abundant
invertebrates of the beaches. It frequently forages along
the foreshore close to cover; in riparian forests of alder,
willow, or cottonwood; in mixed stands of western redcedar,
thimbleberry, and crab apple that surround lakes or beaver
ponds; as well as the edges of forest openings, fields,
sewage ponds, creeksides, roadsides, and muskeg edges. On
the west coast of Vancouver Island, where the Swainson's
Thrush is particularly widespread, it prefers 30- to 35- and
50- to 60 year-old forests of western hemlock, amabilis fir,
Douglas-fir, western redcedar, and Sitka spruce, with red
alder in the wet areas (Bryant et al. 1993).
In wetter parts of the
interior, the Swainson's Thrush occurs in the widespread
coniferous forests of lodgepole pine, Douglas-fir, Engelmann
spruce, white spruce, western larch, and subalpine fir. In
drier areas, it occupies deciduous woodland with scattered
conifers, as well as thickets of black hawthorn, choke
cherry, and saskatoon that occur in the swales and gullies
of grassland slopes. It coexists with the Veery in riparian
cottonwood stands with a dense shrub understorey. In the
north, the Swainson's Thrush occurs in mixed deciduous
woodlands, in forests of white spruce mixed with aspen,
birch, or willow, or where black spruce and tamarack
predominate, and where berry-producing shrubs are
widespread.
The Swainson's Thrush coexists
with other closely related thrushes in British Columbia. In
the southern interior, where it shares habitat with the
Veery, the Swainson's Thrush forages higher above the
ground, and prefers habitat with less undergrowth than that
preferred by the Leery On the Queen Charlotte Islands, where
it shares habitat and perhaps the same food sources with the
Hermit Thrush, the spring migration of the Swainson's Thrush
reaches the islands later than that of the Hermit Thrush.
Thus, although the same resource base may be used by the 2
species, the periods of peak demand are separated (Sealy
1974).
On the south coast, the spring
migration begins in April, or occasionally in very late
March. In early May, numbers increase tenfold. Migration in
the Georgia Depression reaches a peak towards the end of
May. This peak is a little later further north, reaching the
northern mainland Coast and Mountains and Queen Charlotte
Islands in early June. In the southern portions of the
interior, the first birds may arrive as early as the third
week of April in the east and west Kootenays, but not until
early May in the Okanagan; however, the main movement does
not occur until late May or early June. The timetable for
spring arrival is similar further north, and indicates the
rapidity of the northward movement.
The southward migration is more
protracted than the spring movement. In the northern
ecoprovinces, south to the Central Interior, an autumn
migration is difficult to discern. In the Southern Interior
and Southern Interior Mountains, the autumn migration begins
in early August, with a notable movement occurring between
the third week of August and the second week of September.
Most birds have left the north by the end of August and the
southern regions by the end of September. On the coast, the
autumn departure from the Queen Charlotte Islands and the
Northern Mainland Coast is completed about a month before it
is on the Southern Main land Coast and 2 months before the
Georgia Depression. Throughout much of the coast, migration
begins in late July, is at its height in August, and is
completed in September. Exceptions are the Queen Charlotte
Islands, where there are no records after the end of August,
and the Georgia Depression, where there are a few late
autumn records. Rarely are birds recorded in
winter.
In the interior, the Swainson's
Thrush occurs regularly from 18 April to 1 October; on the
coast, it occurs from 23 March to 12 October.
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Breeding
The Swainson's Thrush
undoubtedly breeds throughout its summer range in the
province. On the coast, however, there are no records of
nesting from northern Vancouver Island, from the south
Moresby Island archipelago, or along the entire mainland
coast between Queen Charlotte Strait and the mouth of the
Skeena River.
In northern British Columbia,
nesting has been documented in the Tatshenshini River
valley, Atlin, the Rabbit River valley near Coal River, and
the vicinity of Fort Nelson. Elsewhere across this vast
area, nesting has been recorded only at Junction and
Telegraph creeks, near the south end of Dease Lake (Swarth
1922), and at a number of locations in the Peace Lowland.
Much remains to be learned about the nesting distribution of
the Swainson's Thrush in northern British
Columbia.
The highest numbers for the
Swainson's Thrush in summer occur in the southern Coast and
Mountains and SubBoreal Interior. An analysis of Breeding
Bird Surveys for the Swainson's Thrush in British Columbia
for the period 1968 through 1993 could not detect a net
change in numbers on either coastal or interior
routes.
On the coast, the Swainson's
Thrush nests from sea level to about 930 m elevation. In
summer, Weber (1975) found the Swainson's Thrush to be the
most abundant songbird on Mount Seymour, north of Vancouver,
between 90 and 370 m, while the Hermit Thrush was the most
abundant species between 740 and 1,050 m elevation (Weber
1975). In the interior, the Swainson's Thrush ranges from
valley bottoms to 1,850 m, but in the Southern Interior, few
Swainson's Thrushes are found below 500 m elevation
(Cannings et al. 1987).
Along the coast, this thrush is
a characteristic nesting species in second-growth forests of
Douglas-fir, Sitka spruce, western redcedar, western
hemlock, and grand fir where there is a dense undergrowth of
salal, thimbleberry, huckleberry, salmonberry, and other
fruiting shrubs. Similar habitats are used in the Southern
Interior, where nesting habitat is usually in relatively
undisturbed Douglas-fir and lodgepole pine forests mixed
with trembling aspen, spruce, and willow. In the northern
interior, the Swainson's Thrush frequents mixed spruce,
paper birch, and trembling aspen forests.
Mixed forest was the most
frequently reported nesting habitat class (39%; n = 146),
followed by deciduous stands (17%), coniferous stands (17%),
rural and suburban areas (12%), and shrublands (9%). Most
nests (84%; n = 244) were associated with undisturbed
forest, followed by disturbed forest and shrubland. Nearly
40% (n = 106) of nests were reported from riparian
situations regardless of the general forest type. In New
York, Dilger (1956) found that, of the 5 species of North
American forest thrushes studied, the Swainson's Thrush was
the most closely associated with undisturbed coniferous
growth.
The Swainson's Thrush has been
recorded breeding in the interior between 31 May and 6
August; on the coast it has been recorded from 30 May to 27
August.
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Nests: 
Most nests were placed in trees
(60%; n = 340), including deciduous trees (30%), conifers
(24%), and snags. Shrub and brush tangles (38%) accounted
for most of the other general nest locations. Nests were
built among branches, saddled on a branch, or lodged in the
fork or crotch of a branch (96%; n = 288). A few nests were
found among tree roots or in shrubs, and 1 nest was found on
a post. The heights for 329 nests ranged from ground level
to 24 m, with 60% between 1 and 2 m.
Nests were cups of grass, moss,
leaves, fine twigs, plant fibres, and rootlets.
Eggs:
Dates for 328 clutches ranged
from 30 May to 7 August, with 51% recorded between 14 and 30
June. Sizes of 313 clutches ranged from 1 to 5 eggs
(1E-30,2E-25,3E-72,4E-172, 5E-14), with 54% having 4 eggs.
The incubation period in British Columbia ranged from 11 to
14 days (n = 4). Harrison (1979) gives the incubation period
as 10 to 13 days.
Nest
Success:
 Of
31 nests found with eggs and followed to a known fate, 5
produced at least 1 fledgling, for a nest success rate of
16%.
Young: Dates for 115 broods
ranged from 13 June to 27 August, with 52% recorded between
29 June and 15 July. Sizes of 74 broods ranged from 1 to 5
young (1Y-9, 2Y-23,3Y-18,4Y-23,5Y-1), with 86% having 2 to 4
young. The nestling period in British Columbia is 11 to 14
days (n = 4). Populations breeding in the Georgia Depression
may have 2 broods a year. Ehrlich et al. (1988) state that
the number of broods produced each year is
uncertain.
Brown-headed Cowbird
Parasitism: In British Columbia, 8% of 395 nests found with
eggs or young were parasitized by the cowbird. There was an
additional record of adults feeding a fledged cowbird. The
parasitism rate both on the coast (n = 250) and in the
interior (n = 145) was 8%. Friedmann et al. (1977) report
this species as an infrequent host for the
cowbird.
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Remarks
Two subspecies of Swainson's
Thrush are found in British Columbia. The "Olive-hacked"
Thrush (C. u. almae) occurs east of the Coast Mountains and
Cascade Mountains, while the "Russet-hacked" Thrush (C. Il.
ustulatus) inhabits coastal forests (Bond 1963).
There are 2 banding reports of
the Swainson's Thrush from British Columbia: a bird banded
at Madison, Wisconsin, on 11 September 1961 was recovered at
Okanagan Landing on 8 April 1963; 1 banded near Hays,
Kansas, on 24 May 1973 was recovered near Grand Forks on 21
August 1973.
There are a number of reports
of the Swainson's Thrush before 23 March and after 12
October, including sightings from Christmas Bird Count
locations where the very similar Hermit Thrush is known to
winter. These include Vancouver 27 December 1955-1 (Weber
and Weber 1975) and Pender Islands 28 December 1965-5
(Stevens and Stevens 1966). See also the following Christmas
Bird Counts: Victoria 23 Dec 1961-1 (Stirling 1962a;
Anderson 1976k),1 Jan 1969-1 (Tatum 1970; Anderson 1976~);
Pender Islands 23 Dec 1978-1 (Anderson 1979; McLardy 1979);
Duncan 15 Dec 1979-1 (Comer 1980); White Rock 28 Dec 1975-1
(Anderson 1976a; Schouten 1974); Vancouver 26 Dec 1975-1
(Anderson 1976a;Kautesk 1976); Nanaimo 31 Dec 1977-1 (van
Kerkoerle 1978). All but 3 records, however, lack convincing
details and have been excluded from the account.
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Located
at:
675 Belleville Street,
Victoria, British Columbia,
CANADA
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Copyright © Royal BC Museum
All rights reserved
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This
information was scanned from The Birds of British Columbia (Campbell et
al.), Volume III, pages 394-401. Volumes I, II and III of The Birds of British
Columbia can be ordered electronically at: 
Nests