Swainson's Thrush (Catharus ustulatus)

Distribution

Breeding: From central Alaska and northern Yukon to south-central Manitoba, southern Ontario, Quebec, Labrador, Newfoundland, and Nova Scotia, south through Maine, Vermont, New Hampshire, northwestern Massachusetts, and New York, to northern Pennsylvania. Ranges south in the Appalachians to West Virginia, in the Rocky Mountains to north-central New Mexico, northern Utah, and the White Mountains of Arizona, and in the Sierra Nevadas to southern California. Also in western edge of South Dakota and western Montana. Distinct population on Pacific slope from British Columbia to southern California.

Winter: Winters from southern Mexico to Peru, Brazil, and Argentina. A few individuals may winter in the West Indies.

Breeding habitat

Primarily coniferous or mixed forest dominated by spruce, fir, white cedar, or tamarack. In western mountains and along Pacific coast, often in dense riparian willows or alders. They may be found in both undisturbed or disturbed woodlands with dense understory, often near canopy gaps produced by fallen trees or other disturbances. In the mountains of the Northeast, they are generally found between 1,000–4,500 feet (304–1,370 meters), higher elevations than the Hermit Thrush and lower elevations than the Bicknell’s Thrush. Where there is overlap at the lower elevations, the Hermit Thrush appears to dominate over the Swainson’s Thrush. In the western mountains they occur up to 9,000 feet (2,740 meters) in the spruce-fir zone and to sea level along the Pacific Coast.

Conservation status

The Swainson’s Thrush has a large range and is very common in many areas, yet it is experiencing steady population declines in regions such as California and the Maritime provinces. It is of conservation importance because of its association with many types of coniferous as well as riparian forests for breeding, and because of its vulnerability to tropical deforestation in South America. Understanding how habitat requirements and sensitivity to fragmentation varies over its large range will be important for conserving future populations.

Description

Male: Rich, brownish-olive above with buffy lores and a buffy eye-ring. Breast slightly buffy with dark spots, brownish-gray sides and flanks. The Pacific Coast forms are reddish-brown above and less distinctly spotted below. The eye-ring, cheeks, and breast distinguish it from the similarly colored Gray-cheeked Thrush.

Female: Same as male.

Juvenile: Deep olive-brown above with darker wings and tail; entire upperparts with buffy tips on the feathers. Strongly washed with buff on the throat, breast, and sides; heavily spotted with black on the breast and sides of throat. Pale buffy eye-ring.

Vocalizations

Song: A slurred series of notes spiraling upward in pitch, rather than tumbling downward like the Veery. It is quite complex and variable and has been characterized phonetically as whip-poor-will-a-will-e-zee-zee-zee with the last notes often running together into a high trill. Often sings at night.

Calls: There are three different calls: a clear, slightly inflected whistled note, feee-ee, an abrupt whistle that sounds very similar to the spring peeper, and a loud, sharp whit. The last call note is the most common.

Foraging strategy

Mostly a ground feeder; also forages by gleaning from foliage and occasionally from branches as well as by hawking insects on the wing. Most frequently hunts from a low branch, hopping from perch to perch searching for prey on the ground or within low branches; swoops to pick up prey items in a similar fashion as the Veery. Young are fed insects and possibly some fruit.

Diet

Eats beetles of all kinds, weevils, ants, wild bees, wasps, caterpillars, spruce bud moths, mosquitoes, crane flies, treehoppers, cicadas, and also spiders, millipedes, snails, sowbugs, earthworms, domestic and wild cherries, blackberries, raspberries, seeds of twinberry, and elderberry. Becomes more frugivorous during late summer, fall, and winter.

Behavior and displays

• Often sings from a high perch, but forages on or near the ground.

• May flick its wings and raise its crest when agitated, but rarely raises and lowers its tail like the Hermit Thrush.

• When performing an agonistic display (a behavior used to threaten another bird) the bird draws its head back, raises its bill at approximately a 45°angle while moving its bill slightly to the side.

Courtship

• No information.

Nesting

Nest site: Usually built in a small fir, spruce, hemlock, vine maple, alder, or willow, on a horizontal branch near the trunk.

Height: Typically 4–7 feet (1.2–2meters) above ground; recorded from 0.5–60 feet (0.2–18 meters).

Nest: Bulky, well-made cup of twigs, mosses, bark, grasses, rootlets, wet leaves; lined with lichens, plant fibers, skeletonized leaves, and sometimes animal hair. Often concealed with outer covering of live green moss. More elaborately and neatly constructed than those of other thrushes. The female builds the nest in about 4 days.

Eggs: 3–5, usually 4. Pale blue, evenly spotted with brown, generally more brown about the larger end. Oval with a smooth shell and very little gloss.

Incubation period: Incubation by the female alone, lasts approximately 12–13 days. Incubation begins after the third egg is laid.

Nestling period: Young are altricial (born naked or with a small amount of down, eyes closed, unable to move or feed themselves). The young are fed by both parents, at first by regurgitation and by bringing them small insects. Gradually the insects become larger and some fruit may be substituted if insect prey is not as abundant. They are brooded by the female for the first few days. The nestling’s eyes open at 2–3 days, the feather plumes erupt from the sheaths at 7–10 days, and the young leave the nest at 10–12 days.

Fledgling period: Fledglings have been observed as late as August 10. Little is known of their habits between fledging and fall migration.

Broods: Single brooded.

Cowbird Parasitism: Occasionally a host to cowbirds, around a dozen documented cases.