American robin

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: 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.

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.

Seven subspecies of American robin are recognized. These subspecies intergrade with each other and are only weakly defined.

• The eastern robin (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.
• The Newfoundland robin (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 more red than those of the eastern subspecies.
• The southern robin (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 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.
• The northwestern robin (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.
• The western robin (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.
• The San Lucas robin (T. m. confinis) breeds above 1,000 m (3,300 ft) in the highlands of southern Baja California. This subspecies is particularly distinctive, with pale gray-brown underparts. It is relatively small, and the palest subspecies, with uniform pale gray-brown on the head, face and upperparts. It usually lacks any white spots to the tips of the outer tail feathers, which have white edges. It is sometimes classed as a separate species, but the American Ornithologists' Union regards it as only a subspecies, albeit in a different group from the other six subspecies.
• The Mexican robin (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.

Description

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.

The sexes are similar, but the female tends to be duller than the male, 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. The juvenile is paler in color than the adult male and has dark spots on its breast, 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.

Distribution and habitat

This bird 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 Alaska are known to travel as much as 3.5x further across seasons than robins tagged in Massachusetts.

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).

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.

Conservation status

The American robin has an extensive range, estimated at 16,000,000 km² (6,200,000 sq mi), and a large population of about 320 million individuals. The species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations), and is therefore evaluated as least concern. 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.

Birds in central California of the western subspecies (T. m. propinquus) are considered to be still increasing their range, and this is probably the case elsewhere in the U.S. as well.

Disease

The American robin is a known reservoir (carrier) for West Nile virus. 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.

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, the American robin defends a breeding territory and is less social.

Diet

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), 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.

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 discovered that it can find earthworms underground by simply using its listening skills. 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. They are also attracted to freshly turned earth in gardens, where earthworms and grubs are abundant targets. Occasionally, they may visit bird feeders if mealworms or animal-fat suet is offered.

Threats

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.

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 fledging. 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.

Breeding

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.

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. A new nest is built for each brood, and in northern areas the first clutch is usually placed in an evergreen tree or shrub, while later broods are placed in deciduous trees. The American robin does not shy away from nesting close to human habitations and will frequently construct nests under eaves or awnings on human homes when such locations provide adequate shelter. American robins are not cavity nesters, and so will generally not use a bird house, but will take advantage of artificial nesting platforms.

A clutch consists of three to five light blue 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. While the chicks are still young, the mother broods them continuously. When they are older, the mother will brood them only at night or during bad weather.

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. Even after leaving the nest, the juveniles will follow their parents around and beg for food from them.

Juveniles become capable of sustained flight two weeks after fledging.

The adult male and female both are active in protecting and feeding the fledged chicks until they learn to forage on their own. The adult robin gives alarm calls and dives in a threatening manner towards creatures it considers potential predators, such as approaching cats, dogs and humans. The fledglings are able to fly short distances after leaving the nest. The wings of juvenile birds develop rapidly, and it only takes a couple of weeks for them to become proficient at flying. The cryptically colored young birds perch in bushes or trees for protection from predators.

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 2 years.

Vocalization

The male American robin, as with many thrushes, has a complex and almost continuous song. Its song is commonly described as a cheerily 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. The American robin is often among the first songbirds singing 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.

The American robin also sings when storms approach and again when storms have passed. In addition to its song, the American robin 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 American robins exhibit mostly competitive and territorial behavior, they may still band together to drive away a predator.