Thrushes

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Thrushes

Thrushes are a diverse group of about 305 species of common, medium-sized, perching, song birds ranging from 4.5-13 in (11-33 cm) in body length in the family Turdidae. Thrushes occur world-wide in a wide range of habitats, but mostly in forests .

Some species of thrushes are common in parks and gardens containing shrubs and trees not intensively treated with insecticides . Examples of these familiar species of thrushes include robins , bluebirds , and the European song thrush and blackbird.

Biology of thrushes

The generalized body plan of thrushes includes relatively short wings with rounded tips, a longish, weakly forked or rounded tail, stout legs and feet, and a slender beak. Coloration ranges from all-black, through various combinations of brown, blue, red, and white. The juveniles of most species have spotted breasts, as do the adults of some species.

Many thrushes are accomplished singers, with relatively loud, melodious songs that carry over a rather long distance. The rich songs of thrushes provide a pleasing component of the ambience of spring and early summer in the temperate zones of the world, when these migratory birds are actively establishing and defending their breeding territories.

Most species of thrushes occur in forested or shrubby habitats; others occur in grasslands , tundra , and semi-desert. A wide range of food is eaten by thrushes. Most species feed upon small invertebrates (insects , caterpillars, and earthworms) of diverse types, especially when these birds are raising young, which require a high-protein food. Some species feed on berries during at least part of the year.

Most thrushes, usually the female, build mud-lined, cup-shaped nests of twigs, herbaceous stems, or leaves. The nests are usually located in relatively protected places in trees or shrubs, or on the ground. The young birds are naked and helpless for the first weeks of their life and are fed and tended by both adults. Most species of thrushes raise several broods each year, using the same or different nests each time.

Species of thrushes

Robins are among the world's better known thrushes. The American robin (Turdus migratorius) is probably the native bird with which North Americans are most commonly familiar. The American robin has a brick-red breast and slate-grey back and is very widespread, breeding from the northern limit of trees and tall shrubs, through to southern Mexico. The American robin utilizes a wide range of natural habitats, and it also breeds in parks and gardens. As is implied by the scientific name of the species, the American robin is migratory, spending the non-breeding season in the more southern regions of its breeding range, as far south as Guatemala. The varied thrush (Ixoreus naevius) is a robin-like bird of mature and old-growth conifer forests of western North America .

The European robin (Erithacus rubecula) is the original robin red-breast, after which other, superficially similar species of thrushes were named, such as the American robin. The European robin is common in much of Europe and western Russia, breeding in open forests, shrubby habitats, hedgerows, and parks and gardens.

Another common thrush of Europe and North Africa is the European blackbird (Turdus merula). This species occurs in a wide range of forest types, and also in parks and gardens.

Bluebirds are a familiar group of thrushes in North America. The eastern bluebird (Sialia sialis) occurs in open, shrubby habitats of various types in eastern and central North America and south to Nicaragua. Male eastern bluebirds have a blue back and a red breast, while the color of the female is more subdued. The western bluebird (S. mexicana) and mountain bluebird (S. currucoides) are found in western North America.

Five species of thrushes occur in the forests of North America. These thrushes have a basic coloration of grey-brown to brown-red backs, with a white, spotted breast. All of these birds have pleasing, flute-like songs. These species include the wood thrush (Hylocichla mustelina), hermit thrush (H. guttata), olive-backed thrush (H. ustulata), gray-cheeked thrush (H. minima), and veery (H. fuscescens). Numbers of some of the more southern populations of these forest thrushes appear to be declining substantially, in part because of excessive nest parasitism by the brown-headed cowbird (Molothrus ater). The breeding range of the cowbird has expanded tremendously because of fragmentation of forests by human activities, especially the conversion of forests to agricultural and residential land-use. The cowbird poses a risk for many species of birds, in addition to forest thrushes.

The wheatear (Oenanthe oenanthe) is an arctic species of thrush, breeding as far north as the limits of land in both North America and Eurasia.

Thrushes and people

Because species of thrushes are among the more familiar and well appreciated native birds, they are an important component of the aesthetic environment. This is true of both natural habitats and managed habitats, such as gardens and parks. As such, the activities and songs of a number of species of thrushes provide people with a meaningful link to the more natural aspects of the human experience.

The European blackbird and European song thrush (Turdus philomelos) were introduced to New Zealand and

Australia by British colonists. This was done as part of a larger attempt to make their new, foreign surroundings more familiar in the context of west European culture.

In some places, populations of thrushes have suffered badly as a result of poisoning caused by their exposure to insecticides used in agriculture or for other purposes. For example, during the 1950s and 1960s, populations of American robins declined greatly in places where the insecticide DDT was used to kill the beetle vectors that were spreading Dutch elm disease. The latter is an introduced pathogen that is still killing native elm trees over large areas, including large and valuable trees in cities and suburbs. The disappearance of robins and their prominent, melodious songs was an important component of the so-called "silent spring" that became a metaphor for the ecological damage associated with some types of pesticide uses. As such, the health of robin populations became a very important indicator of the broader health of the urban and suburban environment.

Thrushes seen only occasionally in North America include

White-throated robin (Turdus assimillis). A southwestern stray. Normally a resident of the tropical mountains , this bird has been seen in southern Texas during particularly harsh winters.
Clay-colored robin (Turdus grayi). A southwestern stray. Normally resides from eastern Mexico to northern Columbia, this bird has become a frequent visitor to southern Texas (especially in winter) in recent years.
Redwing (Turdus illacus). An eastern stray. Normally residing in Europe and northern Asia , this bird has been observed several times in North America (mostly in winter).
Dusky thrush (Turdus naumanni). An Alaskan stray. Normally a resident of Asia, this bird has been observed in Alaska on several occasions.
Eyebrowed thrush (Turdus obscurus). An Alaskan stray. Native of Asia. Seen as a rare migrant in the western Aleutian Islands. Has also been observed on the Pribilofs, St. Lawrence Island, and the Alaskan mainland.
Fieldfare (Turdus pilaris). An eastern stray. Common in Europe and parts of northern Asia, this bird is sometimes seen in eastern Canada and the northeastern United States. There have also been sightings in Alaska.
Red-legged thrush (Turdus plumbeus). A native of the West Indies, this bird was once seen in Miami, Florida.
Rufous-backed robin (Turdus rufopalliatus). A southwestern stray. A resident of Mexico, this bird occasionally strays north to southern Arizona. Sightings have also occurred in Texas, New Mexico, and California.

Status of North American thrushes

Eastern bluebird (Sialia sialis) and Western bluebird (Sialia mexicana). Have suffered from the felling of dead trees and the removal of dead branches, which increases competition with other species such as House sparrows and European starlings for nesting cavities. Nest boxes are now used to maintain populations; this has proven more successful with the Eastern Bluebird, but the provision of nesting boxes for Western Bluebirds does not appear to have kept pace with the loss of natural sites. In recent decades, the numbers of Western bluebirds have declined over much of this bird's range. It is estimated that at one point, the Eastern bluebird population had declined by 90% since 1900; today the population seems to be increasing. Rarely, cowbirds may lay eggs in this bird's nests, with the result that fewer young of their own are hatched.
Mountain bluebird (Sialia currucoides). The population of this species has suffered drastic decline since 1900. This bird competes with flickers, swallows, house sparrows, and starlings for nesting locations. But today their numbers appear stable.
Townsend's solitaire (Myadestes townsendi). Rarely, cowbirds may parasitize.
Wood thrush (Hylocichla mustelina). Serious population decline in recent years. May be losing winter habitat in tropics. Cowbirds may parasitize.
Veery (Catharus fuscescens). Brown-headed Cowbirds may parasitize. Surveys suggest that this bird's numbers are declining.
Swainson's thrush (Catharus ustulatus). This bird no longer breeds along the Pacific Coast as it once did, although the overall population appears stable. It may be vulnerable to loss of breeding grounds. Rarely, cowbirds may parasitize.
Gray-cheeked thrush (Catharus minimus). The southern breeding populations may be in decline.
Bicknell's thrush (Catharus bicknelli). The Bicknell's thrush of the Northeast, which winters mostly on the island of Hispaniola in the West Indies, is currently being watched by conservationists. Although the Bicknell's Thrush looks and sounds very much like the Gray-cheeked Thrush, it is now considered to be a separate species. Unlike most Gray-cheeked thrushes, which breed in northern spruce forests and in thickets of willow and alder on the tundra, the Bicknell's thrush breeds in stunted conifers on the tops of mountains and in dense second-growth woods containing many young conifers.
Hermit thrush (Catharus guttatus). Numbers appear to be holding up. Because it winters farther north than other brown thrushes, it less threatened by ecological damage to the tropics. Rarely, cowbirds may parasitize.
Varied thrush (Ixoreus naevius). Although still common, this bird may be vulnerable to loss of habitat due to cutting of forests of the Northwest.
American robin (Turdus migratorius). Rarely, cowbirds may parasitize. Has expanded into Great plains and drier lowlands with the planting of trees and the extension of irrigation (creating nesting sites and moist grassland for foraging). Although this bird was once widely hunted for food, it is today abundant and widespread.
Northern wheatear (Oenanthe oenanthe). The population in North America appears stable, but this bird may be increasingly seeking out breeding grounds in northeastern Canada.
Bluethroat (Luscinia svecica). This small Alaskan population is probably stable, and possibly even increasing. Widespread and common in Eurasia.