American Robin

识别特征

The eastern subspecies of the American robin (T. m. migratorius) is 23 to 28 cm (9.1 to 11.0 in) long with a wingspan ranging from 31 to 41 cm (12 to 16 in), with similar size ranges across all subspecies. The species averages about 77 g (2.7 oz) in weight, with males ranging from 72 to 94 g (2.5 to 3.3 oz) and females ranging from 59 to 91 g (2.1 to 3.2 oz). Among standard measurements, the wing chord is 11.5 to 14.5 cm (4.5 to 5.7 in), the culmen is 1.8 to 2.2 cm (0.71 to 0.87 in) and the tarsus is 2.9 to 3.3 cm (1.1 to 1.3 in). The head varies from jet black to gray, with white eye arcs and white supercilia. The throat is white with black streaks, and the belly and undertail coverts are white. The American robin has a brown back and a reddish-orange breast, varying from a rich red maroon to peachy orange. The bill is mainly yellow with a variably dark tip, the dusky area becoming more extensive in winter, and the legs and feet are brown.<p>The sexes are similar, but females tend to be duller in color than males, with a brown tint to the head, brown upperparts, and less-bright underparts. However, some birds cannot be accurately sexed on the sole basis of plumage. Juveniles are paler in color than adult males and have dark spots on their breasts and whitish wing coverts. First-year birds are not easily distinguishable from adults, but they tend to be duller, and a small percentage retain a few juvenile wing coverts or other feathers.

分类信息

This species was first described in 1766 by Carl Linnaeus in the twelfth edition of his Systema Naturae as Turdus migratorius. The binomial name derives from two Latin words: turdus, "thrush", and migratorius from migrare "to migrate". The term robin for this species has been recorded since at least 1703. There are about 65 species of medium to large thrushes in the genus Turdus, characterized by rounded heads, longish pointed wings, and usually melodious songs.<p>A study of the mitochondrial cytochrome b gene indicates that the American robin is not part of the Central/South American clade of Turdus thrushes; instead it shows genetic similarities to the Kurrichane thrush (T. libonyanus) and the olive thrush (T. olivaceus), both African species. This conflicts with a 2007 DNA study of 60 of 65 Turdus species, which places the American robin's closest relative as the rufous-collared thrush (T. rufitorques) of Central America. Though having distinct plumage, the two species are similar in vocalization and behavior. Beyond this, it lies in a small group of four species of otherwise Central American distribution, suggesting it recently spread northwards into North America.<p>Seven subspecies of American robin are recognized. These subspecies intergrade with each other and are only weakly defined.

学名

Turdus migratorius

命名信息

Linnaeus, 1766

目

Passeriformes

科

Turdidae

属

Turdus

分布与栖息地

The American robin breeds throughout most of North America, from Alaska and Canada southward to northern Florida and Mexico. While robins occasionally overwinter in the northern part of the United States and southern Canada, most migrate to winter south of Canada from Florida and the Gulf Coast to central Mexico, as well as along the Pacific Coast. Most depart south by the end of August and begin to return north in February and March (exact dates vary with latitude and climate). The distance by which robins migrate varies significantly depending on their initial habitat; a study found that individual robins tagged in Alaska are known to travel as much as 3.5x further across seasons than robins tagged in Massachusetts.<p>This species is actually a rare vagrant to western Europe, where the majority of records, more than 20, have been in Great Britain. In the autumn of 2003, migration was displaced eastwards leading to massive movements through the eastern U.S., and presumably this is what led to no fewer than three American robins being found in Great Britain, with two attempting to overwinter in 2003–2004, although one was taken by a Eurasian sparrowhawk. A sighting occurred in Great Britain in January 2007. This species has also occurred as a vagrant to Greenland, Jamaica, Hispaniola, Puerto Rico and Belize. Vagrants to Europe, where identified to subspecies, are the eastern subspecies (T. m. migratorius), but the Greenland birds also included the Newfoundland subspecies (T. m. nigrideus), and some of the southern overshots may have been the southern subspecies (T. m. achrusterus).<p>The American robin's breeding habitat is woodland and more open farmland and urban areas. It becomes less common as a breeder in the southernmost part of the Deep South of the United States and there prefers large shade trees on lawns. Its winter habitat is similar but includes more open areas.<p>The American robin is a known reservoir (carrier) for West Nile virus spread by Culex mosquitoes. While crows and jays are often the first noticed deaths in an area with West Nile virus, the American robin is suspected to be a key host and holds a larger responsibility for the transmission of the virus to humans. This is because, while crows and jays die quickly from the virus, the American robin survives the virus longer, hence spreading it to more mosquitoes, which then transmit the virus to humans and other species.<p>A successful West Nile virus vaccine has been administered to six 3-5 week old American robins. A DNA vaccine injected intramuscularly resulted in a 400-fold decrease in average viral load that would likely make robins noninfectious and unable to spread disease. An oral bait is the preferred method of distribution of the vaccine as it would be easier and cheaper than intramuscular injection, but more research would be needed as the existing formulation did not work orally.

迁徙

Complete migrants

行为

The American robin is active mostly during the day, and on its winter grounds, it assembles in large flocks at night to roost in trees in secluded swamps or dense vegetation. The flocks break up during the day when the birds feed on fruits and berries in smaller groups. During the summer, the American robin defends a breeding territory and is less social.<p>The American robin's diet generally consists of around 40 percent small invertebrates (mainly insects), such as earthworms, beetle grubs, caterpillars, and grasshoppers, and 60 percent wild and cultivated fruits and berries. Their ability to switch to berries allows them to winter much farther north than most other North American thrushes. They will flock to fermented Pyracantha berries, and after eating sufficient quantities will exhibit intoxicated behavior, such as falling over while walking. Robins forage primarily on the ground for soft-bodied invertebrates, and find worms by sight (and sometimes by hearing),: 149  pouncing on them and then pulling them up. Nestlings are fed mainly on earthworms and other soft-bodied animal prey. In some areas, robins, particularly of the northwestern subspecies (T. m. caurinus), will feed on beaches, taking insects and small mollusks. American robins are common pests of fruit orchards in North America. Due to their insectivorous and frugivorous diet they have evolved to lose sucrase. Sucrose is unpalatable to them and can be used by humans as a deterrent.<p>The American robin uses auditory, visual, olfactory and possibly vibrotactile cues to find prey, but vision is the predominant mode of prey detection. It is frequently seen running across lawns picking up earthworms, and its running and stopping behavior is a distinguishing characteristic. In addition to hunting visually, it also has the ability to hunt by hearing. Experiments have shown that it can find earthworms underground by simply using its listening skills.: 149  It typically will take several short hops and then cock its head left, right or forward to detect movement of its prey. In urban areas, robins will gather in numbers soon after lawns are mowed or where sprinklers are in use.<p>Juvenile robins and eggs are preyed upon by squirrels, snakes, and some birds, such as blue jays, California scrub jays, Steller's jays, common grackles, American crows, and common ravens. Adults are primarily taken by Accipiter hawks, cats, and larger snakes (especially rat snakes and gopher snakes). Mammals, such as foxes and dogs, are mainly likely to grab fledgling young robins from the ground, while raccoons often prey upon nests, and small carnivores such as American martens, ring-tailed cats and long-tailed weasels are agile enough to hunt adults. However, the greatest predatory impact (perhaps alongside domestic cats) is probably from raptorial birds. They may be taken by nearly every variety of North American accipitrid, from the smallest, the sharp-shinned hawk, to one of the two largest, the golden eagle, most every North American falcon from the smallest, the American kestrel, to the largest, the gyrfalcon, and almost all owl species from the northern pygmy owl to the snowy owl. Overall, 28 raptorial bird species are known to hunt American robins. Adult robins are most vulnerable when distracted by breeding activities, though they may also be attacked on the ground or even in flight. However, when feeding in flocks, the American robin is able to remain vigilant and watch other flock members for reactions to predators.<p>The American robin is known to be a rejecter of cowbird eggs, so brood parasitism by the brown-headed cowbird is rare. Even when it occurs, the parasite's chick does not normally survive to fledge. In a study of 105 juvenile robins, 77.1% were infected with one or more species of endoparasite, with Syngamus species the most commonly encountered, found in 57.1% of the birds.<p>The American robin begins to breed shortly after returning to its summer range. It is one of the first North American bird species to lay eggs, and normally has two to three broods per breeding season, which lasts from April to July.<p>The nest is most commonly located 1.5–4.5 m (4.9–14.8 ft) above the ground in a dense bush or in a fork between two tree branches, and is built by the female alone. The outer foundation consists of long coarse grass, twigs, paper, and feathers. This is lined with smeared mud and cushioned with fine grass or other soft materials. The American robin builds a new nest for each brood; in northern areas the nest for the first clutch will usually be located in an evergreen tree or shrub, while later broods are raised in deciduous trees. The species is not shy about nesting close to human habitations.<p>A clutch consists of three to five cyan-colored eggs, and is incubated by the female alone. The eggs hatch after 14 days, and the chicks leave the nest a further two weeks later. The altricial chicks are naked and have their eyes closed for the first few days after hatching.<p>The chicks are fed earthworms, insects, and berries. Waste accumulation does not occur in the nest because the adults collect and take it away. Chicks are fed, and then raise tails for elimination of waste, a solid white clump that is collected by a parent prior to flying off. All chicks in the brood leave the nest within two days of each other. Juveniles become capable of sustained flight two weeks after fledging. Chicks become sexually mature at one year of age. Bird banders have found that only 25% of young robins survive their first year. The longest known lifespan of an American robin in the wild is 14 years; the average lifespan is about two years.<p>The male American robin, as with many thrushes, has a complex and almost continuous song. It is commonly described as a cheery carol, made up of discrete units, often repeated, and spliced together into a string with brief pauses in between. The song varies regionally, and its style varies by the time of day. The song period is from late February or early March to late July or early August; some birds, particularly in the east, sing occasionally into September or later. They are often among the first songbirds to sing as dawn rises or hours before, and last as evening sets in. It usually sings from a high perch in a tree. The song of the San Lucas subspecies (T. m. confinis) is weaker than that of the eastern subspecies (T. m. migratorius), and lacks any clear notes.<p>The American robin also sings when storms approach and again when storms have passed. In addition to its song, the species has a number of calls used for communicating specific information, such as when a ground predator approaches and when a nest or another American robin is being directly threatened. Even during nesting season, when they exhibit mostly competitive and territorial behavior, they may still band together to drive away a predator.

保护状况

The American robin has an extensive range, estimated at 16,000,000 km2 (6,200,000 sq mi), and a large population of about 370 million individuals. The western subspecies (T. m. propinquus) in central California is considered to be expanding its range, as is likely the case elsewhere in the United States. It is threatened by climate change and severe weather, but the population trend appears to be stable, and the species does not approach the vulnerable species thresholds under the population trend criterion (&gt;30% decline over ten years or three generations), and therefore International Union for Conservation of Nature evaluated it as least concern.<p>At one point, the bird was killed for its meat, but it is now protected throughout its range in the United States by the Migratory Bird Treaty Act.

种群趋势

stable