Meet the Swainson’s Thrush (Catharus ustulatus), a charming songbird slightly smaller than a robin. These tweeters come in two color morphs – olive-backed and russet-backed – making them a bit more difficult to identify, especially considering how many similar species there are.
Here is all you need to know about them to make your life a bit easier.
Identification
Swainson’s Thrushes are medium-sized songbirds measuring between 6.3 to 7.5 inches long with a wingspan of 11.4 to 12.2 inches. They are slightly smaller than robins but have a similar body shape with fairly slim bodies, rounded bellies, round heads, fairly long wings, and medium-length tails.
Russet-backed morph
Due to the length of the wings and tail, the bird may appear to have a long back half. They have dark eyes, short dark bills, and dull pink legs.
Male and female Swainson’s Thrushes look identical. However, there are two color morphs called the olive-backed and the russet-backed. The olive-backed morph has brownish-olive uppersides and head, their underside is white with brownish spotting on the throat and chest which becomes smudged and more olive-toned on their bellies. They have a distinct pale, almost white eye ring.
The russet-backed morph has a similar plumage pattern with the main difference residing in coloration. They have medium brown upperparts with a rusty hue to them, pale brown flanks, and brown spots on their throat and chest which become paler and less defined further down on the belly. The pale eye-ring is slightly less conspicuous.
Vocalizations
The song of Swainson’s Thrush varies slightly from bird to bird, but all of them share similar characteristics. It is a series of reedy, upward-spiraling flute-like notes that can generally be described as whip-poor-will-a-will-e-zee-zee-zee. Males sing it to defend their territories and nests and to attract females.
They also have various one- or two-noted calls. Overall, the calls of russet-backed Swainson’s Thruses tend to be more liquid, whereas olive-backs have sharper calls.
Birds expressing alarm or trying to distract intruders emit a sharp whit or whit-burr. Migrating birds give a hollow peep sound. They also give thin, single-noted high-pitched whines, drawn-out metallic peeer, and a sound similar to water dropping onto a hard surface.
Food
The diet of Swainson’s Thrushes includes both plant and animal matter. Their specific dietary choices depend on the season and what is currently available.
During the breeding season, they seem to prefer insects and other invertebrates, including beetles, ants, bees, wasps, true bugs, grasshoppers, caterpillars, flies, crickets, moths, spiders, and others.
However, during the fall and winter, they go for berries and soft fruit. They seem to prefer red ones and dislike yellow ones. Their favorite ones include elderberries, raspberries, huckleberries, blackberries, twinberries, sumac, and other wild fruits.
Swainson’s Thrushes forage on various levels, from the ground to bushes to trees. If they forage on the ground, they hop from one spot to the next, inspecting the ground for insects and other invertebrates.
They may also perch on branches and perches close to the ground to survey the surroundings and then pounce on unsuspecting prey.
While foraging in the foliage, they take short hops along branches stopping to insect every once in a while. They glean food from the branches and leaves of both deciduous and coniferous trees. May also hover briefly to snatch insects from foliage or dart out to catch them mid-air.
Nesting and Eggs
Swainson’s Thrushes are presumed to be monogamous for the duration of the breeding season. Males arrive on the breeding grounds first and establish and defend their territories by singing.
They chase off any intruders, including females. The pair bond starts forming once a female chooses to stay in the male’s territory.
Olive-backed morph
At first, the male chases the female and sings to her, with the chasing de-escalating into slow flights and perching together over time. After about 3-4 days, they will have bonded.
Swainson’s Thrushes nest in concealed places on a horizontal branch in the forest understory around 3-10 feet above the ground.
In the east and north, they prefer conifers, whereas in the west, they prefer deciduous trees or shrubs.
Females build the nest themselves, which is a compact cup 1.5-4 inches high and 3.5-6 inches across. She weaves it of stems, fine twigs, decayed leaves, grass, bark shreds, and sometimes mud and lines it with rootlets, hair, lichens, moss, and other soft materials.
This thrush has only one brood in a year but may attempt a second, albeit a smaller one, if the first one fails early in the season. They lay 1-5, usually 4 eggs in a clutch.
Swainson’s Thrush eggs are pale blue to greenish blue speckled with brown or rust-colored spots, measuring 0.8-1 inches long and 0.6-0.7 inches wide. Females incubate the eggs for 9-14 days while the male provides her with food. Both parents feed their offspring.
The young fledge, leave the nest, and gain independence around 10-14 days after hatching.
Current Situation
Swainson’s Thrushes range throughout North and Central America and parts of western South America. They mostly breed in Alaska and Canada, along the western coast of the United States, parts of the northwestern United States, and the most northeastern United States.
Migration takes them over the rest of the United States to Central and South America for the winter.
Swainson’s Thrushes inhabit forests with lots of undergrowth. They breed at an altitude from sea level to 8,500 feet and tend to favor areas with complete canopy cover and higher tree density.
In the western regions of North America, they can be found in riparian woodland forests and conifer forests. In contrast, in the eastern regions, they live in a combination of hardwood and coniferous forests.
During migration, their habitat range becomes more varied and includes canyon bottoms, swamp forests, forest edges, parks, and other areas with dense undergrowth.
Swainson’s Thrush is listed as a species of least concern on the IUCN Red List. They are common and seem to have a steady population. Main threats include disruptions to nesting, collision with man-made objects, and habitat loss and fragmentation.
Facts About Swainson’s Thrushes
- Swainson’s Thrush has six recognized subspecies that are divided into two groups – the russet-backed and the olive-backed thrushes or the coastal and the inland forms respectively. In North America, russet-backs can mainly be seen along the west coast whereas the olive-backed ones in the north and east. The former winters in Central America whereas the latter in South America.
- Swainson’s Thrushes typically live for around one to two years in the wild. The oldest individual on record lived to be at least 12 years and 1 month old.
- Another name for a Swainson’s Thrush is the mosquito thrush for its habit of snatching insects mid-air.
- Although Swainson’s Thrushes usually sing in an ascending pitch, then during territorial disputes males may invert that so that the melody spirals downward instead. If this does not end the conflict, then it can escalate to chasing and even physical altercations.
Similar Species
Swainson’s Thrushes look similar to many other thrush species, including the Hermit Thrush, Veery, Bicknell’s Thrush, Gray-cheeked Thrush, and Wood Thrush. Here are the three most similar species and how to tell them apart.
Hermit Thrush
Hermit Thrushes have a fairly similar range in North America, but there are some differences. Adults are brown above and pale below with brown spots on the throat and smudgy ones on the chest.
They are more similar to the russet-backed form of the Swainson’s Thrush but can be distinguished by their distinct white instead of buffy eye-ring and bright cinnamon instead of simple brown tail.
Veery
Veerys breed across the northern United States and southern Canada and migrate to South America for the winter.
They are bright cinnamon above and whitish below with pale cinnamon throat, dark spotting on the throat, and faint and very smudgy spotting on the chest.
Veerys are more similar to the russet-backed form. However, they are warmer and have a more reddish plumage, a much fainter eye-ring, and less obvious spotting on the chest.
Frequently Asked Questions
What is another name for Swainson’s Thrush?
Another name for Swainson’s Thrush would be the mosquito thrush.
What is the difference between a Hermit Thrush and a Swainson’s Thrush?
Hermit Thrushes have a thin white eye-ring instead of a buffy one and a reddish cinnamon tail instead of a plain brown one like the Swainson’s Thrush has.
What is the difference between Wood Thrush and Swainson’s Thrush?
Wood Thrushes are larger than Swainson’s Thrushes, they have a distinct white eye-ring instead of a buffy one, and very dark, almost black spotting that doesn’t fade like the Swainson’s spotting does.
What is the difference between a thrasher and a thrush?
Thrashers are from the Mimidae family whereas thrushes are from the Turdidae family. Thrushes are generally smaller with plump bodies and rounded wings whereas thrashers tend to be larger and more slender with longer tails.
What do Swainson’s thrush eat?
Swainson’s Thrushes eat various insects, other invertebrates, and soft fruit and berries.
