American robin

The American robin is a migratory bird of the true thrush genus and Turdidae, the wider thrush family. It is named after the European robin because of its reddish-orange breast, though the two species are not closely related, with the European robin belonging to the Old World flycatcher family. The American robin is widely distributed throughout North America, wintering from southern Canada to central Mexico and along the Pacific coast.
According to the Partners in Flight database, the American robin is the most abundant landbird in North America, ahead of red-winged blackbirds, introduced European starlings, mourning doves and house finches. It has seven subspecies.
The species is active mostly during the day and assembles in large flocks at night. Its diet consists of invertebrates, fruits, and berries. It is one of the earliest bird species to lay its eggs, beginning to breed shortly after returning to its summer range from its winter range. The robin's nest consists of long coarse grass, twigs, paper, and feathers, and is smeared with mud and often cushioned with grass or other soft materials. It is among the earliest birds to sing at dawn, and its song consists of several discrete units that are repeated.
The adult's main predator is the domestic cat; other predators include hawks and snakes. When feeding in flocks, it can be vigilant, watching other birds for reactions to predators. Brown-headed cowbirds lay their eggs in robin nests, but the robins usually reject the egg.

Taxonomy

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: ', "thrush", and ' from ' "to migrate". The term ' for this species has been recorded since at least 1703.
A 2020 genetic study has shown that the American robin is closest to the rufous-collared thrush of Central America, confirming a 2007 study which also placed this as its closest relative. Though having distinct plumage, the two species are similar in vocalization and behavior. Beyond this, it lies in a group of other Central American thrushes, suggesting a recent spread northwards into North America; the 2007 study suggested rufous-backed thrush as the next closest relative, with both studies giving the next-closest relatives beyond this trio as the species pair of black thrush and sooty thrush, also of Central America.
These results contrast markedly with two older studies of the mitochondrial cytochrome b gene which had suggested, though only with weak support, that the American robin might be more closely related to the Kurrichane thrush and the olive thrush, both African species, rather than other American thrushes.

Subspecies

Seven subspecies are accepted. These, except for the isolated T. m. confinis, intergrade with each other and are only weakly defined.

T. m. nigrideus breeds from coastal northern Quebec to Labrador and Newfoundland and winters from southern Newfoundland south through most of the eastern U.S. states to southern Louisiana, southern Mississippi, and northern Georgia. It is uniformly darker or blackish on the head, with a dark gray back. The underparts are slightly richer red than those of the nominate subspecies.
T. m. migratorius, the nominate subspecies, breeds in the U.S. and Canada, other than down the West Coast, to the edge of the tundra from Alaska and northern Canada east to New England and then south to Maryland, northwestern Virginia, and North Carolina. It winters in southern coastal Alaska, southern Canada, most of the U.S., Bermuda, the Bahamas and eastern Mexico.
T. m. achrusterus breeds from southern Oklahoma east to Maryland and western Virginia and south to northern Florida and the Gulf Coast states. It winters through much of the southern part of the breeding range. It is marginally smaller than the eastern subspecies. The black feathers of the forehead and crown have pale gray tips. The underparts are paler than those of the eastern subspecies.
T. m. caurinus breeds in southeastern Alaska through coastal British Columbia to Washington and northwestern Oregon. It winters from southwestern British Columbia south to central and southern California and east to northern Idaho. It is slightly smaller than the eastern subspecies and very dark-headed. The white on the tips of the outer two tail feathers is restricted.
T. m. propinquus breeds from southeastern British Columbia, southern Alberta, and southwestern Saskatchewan south to southern California and northern Baja California. It winters throughout much of the southern breeding range and south to Baja California. It is the same size as, or slightly larger than, the eastern subspecies, but paler and tinged more heavily brownish-gray. It has very little white on the tip of the outermost tail feathers. Some birds, probably females, lack almost any red below. Males are usually darker and may show pale or whitish sides to the head.
T. m. phillipsi is resident in Mexico south to central Oaxaca. It is slightly smaller than the western subspecies, but has a larger bill; the male's underparts are less brick-red than the eastern subspecies and have a rustier tone.
T. m. confinis breeds above in the Sierra de la Laguna mountains of southern Baja California. This isolated non-migratory subspecies is particularly distinctive. It is relatively small, and the palest subspecies, with uniform pale gray-brown on the head, face, and upperparts, and pale buffy orange underparts. It usually lacks any white spots to the tips of the outer tail feathers, which have white edges. It has sometimes been classed as a separate species, but both the American Ornithologists' Union and the IOC World Bird List regard it as only a subspecies, albeit in a different group from the other six subspecies.
Description

The eastern subspecies is long with a wingspan ranging from, with similar size ranges across all subspecies. The species averages about in weight, with males ranging from and females ranging from. Among standard measurements, the wing chord is, the culmen is and the tarsus is. 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 adult 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.
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, with first-year males resembling adult females, and a small percentage retain a few juvenile wing coverts or other feathers.

Distribution and habitat

The species 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. The distance by which they migrate varies significantly depending on their initial habitat; a study found that individual robins tagged in Alaska are known to travel as much as 3.5 times farther across seasons than robins tagged in Massachusetts.
The species is a rare vagrant to western Europe, where the majority of records have been in Great Britain, where 29 had been recorded up to the end of 2022. The species has occurred as a vagrant to Greenland, Sweden, Jamaica, Hispaniola, Puerto Rico and Belize. Vagrants to Europe, where identified to subspecies, are the eastern subspecies, but the Greenland birds included the Newfoundland subspecies, and some of the southern overshots may have been the southern subspecies.
The 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.

Diseases

The species is a known reservoir 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.
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.

Behavior

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, males defend a breeding territory and are less social.