American robin, Turdus migratorius

Taxonomy

Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Sarcopterygii - Tetrapoda - Amniota - Sauropsida - Sauria - Archosauria - Dinosauria - Saurischia - Theropoda - Coelurosauria - Aves - Neognathae - Passeriformes - Turdidae - Turdus - Turdus migratorius

Turdus migratorius

The American robin is a member of Turdidae (thrushes) family. Thrushes belong to order Passeriformes (passerine birds or perching birds). Of the 10,000 or so extant species of birds, over half (~5,300) are perching birds.

Several subspecies of Turdus migratorius are recognized. Turdus migratorius migratorius has the largest range occupying most of the northern half of the United States and Canada (except the Maritime Provinces).

Brief facts

• Description

  The American robin is the most familiar perching bird and the largest thrush in North America. It has a mean total length of 25 cm (9.8 inches) and weighs ~77 g. Mean wing length of birds from the eastern and north-central United States is approx. 12.5 cm (~9 inches). Males are larger than females in most measurements. Mature birds have cinnamon-red to brick-red belly and chest, gray to gray-brown back and wings, dark heads, white throats streaked with black, white marks above and below the eyes, and a yellow bill. Female birds' plumage is paler less conspicuous. Juveniles are similar but paler than mature birds with dark spotting on the underparts, pale spotting on the upperparts and wing coverts, entirely white throat, and less defined white markings around the eye.

• Distribution

  American robins are the most widespread North American thrush. They are found throughout North America except for extreme northern Alaska, Canada, and Greenland. The smallest robins inhabit warm, humid eastern United States, and the largest occur in the high, cool, and dry Rocky Mountains, northern Great Plains, and northern deserts. Territory of North America south of boundary between United States and Canada and north of the boundary between the United States and Mexico represents year-round range of American robins. In southern Florida, Louisiana, and Texas, and in a portion of the southwest desert American robins overwinter but do not breed.

• Ecology and habitat

  American robins inhabit many diverse environments preferring areas of open ground or short grass for foraging, with woodland or a few scattered trees and shrubs nearby for nesting and roosting. In all kinds of environment they tend to select habitats that are close to or within of areas populated by humans in either agricultural or urban settings. For nesting, food and water availability appears to be a primary requirement because areas without trees and with little other vegetation can be inhabited with nest built on or very close to the ground.

• Migrations

  Large complex seasonal migrations of American robins occur over most of North America. Spring migrations generally begin with aggregations of large wintering roosts. These aggregations start to move northward toward breeding sites. Fall migrations of the American robin begin with individual birds becoming more gregarious around early August. Birds, however, may not leave until couple of months later.

• Diet

  American robins are generalists. They eat fruits representing over 50 genera of plants most of them from the family Rosaceae (especially, from genus Prunus) as well as invertebrates representing over 100 families (worms, larvae, beetles, butterflies, etc.). Killing and eating of small vertebrates such as juvenile reptiles (lizards and snakes) was documented. It was found that proportion of fruit (by volume) in the diet was much higher in the fall and winter than in the spring.

• Predators and diseases

  Common nest predators include squirrels, jays, snakes, and falcons. Adults are killed by avian predators such as sharp-shinned hawk (Accipter striatus), Cooper's hawk (Accipiter cooperii), and northern goshawk (Accipiter gentiles), poisoning, and infectious disease. In suburban areas, house cats can be a major predator. Insecticides has also been shown to have negative effects on American robin populations. Major diseases that are known to cause mortality in American robins include Yersinia tuberculosis, avian pox, and an unidentified protozoan. Body parasites such as lice, flies, ticks and mites, and internal parasites such as worms are common. The American robin can host tick Ixodes dammini and serve as a reservoir for Lyme disease caused by pathogen spirochete Borrelia burgdorferi.

• Longevity and mortality

  Potential longevity of the species (the maximum life span that can be attained by an individual of the species) for American robin is at least 13 years and, perhaps as much as 20 years. Average longevity in captivity is about 5.1 years.
  Potential natural longevity is the maximum life span that can be attained in nature. The best estimates of this can be obtained from the greatest ages attained by banded wild birds. For American robin this value is at least 9 years. The turnover period is the time required for birds hatched in the same season to shrink to statistical zero. For robins, the turnover is about 6 years.
  Estimated average natural longevity of robins that survive their first November is about 1.7 years. The mortality rate for birds that pass their first November is slightly more than 50% per annum.

Developmental stages (life cycle)

• Embryo
  • Before laying The embryo is located inside the bird; preparation of egg to laying (shell formation).
  • After laying Embryo development in the egg takes 12-14 days.
• Hatching Each chick takes about 24 hours to hatch and breaks free of the egg by pipping a ring of fractures around the circumference of the egg with its egg tooth.
• After hatching
  • Nestling Young bird remaining in the nest. Hatchlings are altricial. Hatchling' mass ranges from 4.1 – 6.7 grams (mean=5.5 g). The slit between the eyelids is open when the chick hatches, but are held closed intil the fifth day when they open for some periods of time. By the seventh day the eyes are opened most of the time. Around this time sense of instinctive fear that may manifest in squeals also develops. At hatching the young can raise their heads for food only for a second or two. Nestlings are fed regurgitated food for the first 3-4 days after hatching. After that, parents bring a variety of soft invertebrates and fruits. After approximately seven days, nestlings develop homeothermy. By this time they weigh 36-59 gramm.
  • Fledgling Young birds that left the nest and are still dependent on their parents. The earliest age at which young leave the nest is 10 days. At this age they weigh about 62 gramm. Fledglings wander off for a short distance from the nest and are fed by the parents for a period of at least three weeks.
  • Subadult Immature bird. At about four weeks of age, juvenile birds can fly and feed independently. They are of adult proportions and weigh approx. 70-80 gramm.
  • Mature adult Birds with mature reproductive organs, capable of breeding at about 1 year of age. As a rule, individual birds return each spring to the same nesting territory each year.
    • Before pairing During courtship male singing plays a prominent role. During each day there are two outstanding periods of song. The robin is one of the first birds to begin singing in the morning before the sun rise as early as 3 AM (late May, eastern U.S.). Singing intensity subsides around noon and increases once again in the evening twilight following sunset. Thus, the American robin has the longest period of musical activity of the common songbirds. In the courtship both voice and display are important. While displaying the male spreads and elevayes his tail, shakes his wings, and inflates its throat. Both display and mating usally occur on the ground. A pair of robins usually remains mated for the duration of the entire nesting period.
    • Pairing
    • Nesting Throughout its range American robins are one of the earliest passeriform birds to begin nesting. The period lasts from early April to late July. Nesting density varies with roughly 3-4 pairs nests per acre. Robins usually share their nesting territory with other species such as mourning doves, blue jays, catbirds, finches, chipping and song sparrows, cardinals, etc. Robins will usually fight with other individuals of the species which enter their territory. The females are usually more vigorous than the males in the defense of the nest proper. The defense consists of dashing, chirping loudly, snapping the bill and erecting feathers.
      • Nest site choosing Both birds work together in selecting the site for the nest. Robins have remarkably plastic nesting site requirements. The nest is sometimes on the ground, or it may be as high as 80 feet above the ground. Majority of nests are built 2-10 ft. above ground, usually against a tree trunk. During the first nesting, birds prefer evergreens and after first brood, deciduous trees are preferred.
      • Nest building In most cases, only female builds the nest. The building of the nest can be divided into three stages: (1) foundation (outer wall of the nest composed of long coarse twigs and grass stems; (2) forming the mud layer (mud is incorporated into the outer frame, at the same time, grass is meshed into the hardening mud); (3) lining the nest with finer grass material. Nest is bowl-shaped; usually is greater in breadth than in height. Outside diameter is 13-14 mm; inside diameter is 8-10 mm.
      • Egg laying American robins lay 3-4 eggs at approx. rate 1 egg/day around 10 A.M. Maximum number of eggs is 5. Up to three consecutive clutches within one breeding are possible. Eggs are approx. 28.5 mm (~1+ inch) in length and weigh about 6.3 grams.
      • Incubation Incubation starts when the female begins to sit on her eggs without interruption, and ends when the young robin breaks free of the egg shell. Incubation takes 12-14 days. The female incubates for periods of about 40 minutes, after which she stands on the rim of the nest, turns eggs, and flies off for a break.
      • Hatching &
        raising offspring Eggs generally hatch in the order they were laid over a period of 2 – 3 days. Female American robins carry off egg shell fragments after chicks hatched and may eat them. Female American robins brood young for approximately 7 days after hatching until nestlings develop homeothermy. After that female stays on the nest at night or bad weather. Nestlings are fed regurgitated food for the first four days after hatching. Both parents feed nestlings, delivering 6 – 7 feedings each hour to a single nestling, totaling 35 – 40 total feedings a day to each nestling. Robins feed their young about 3.2 pounds of food during the 2 weeks while in the nest. During the nesting period, adults take care of nest sanitation by eating, or later, carrying away fecal sacs produced by the nestlings. Female American robins follows the fledglings at first, later only the male does. The female will begin a second nest at which time the male leads the juvenile birds to a communal roost site.

Photo gallery

 
 
 
 
 
 
 
 
 
 
 

Video

American robin foraging

References

• Dewey, T. and C. Middlebrook. 2001. "Turdus migratorius" (On-line), Animal Diversity Web. Accessed August 27, 2011 http://animaldiversity.ummz.umich.edu/site/accounts/information/Turdus_migratorius.html.
• Trost RE and Malecki RA. Population Trends in Atlantic Flyway Canada Geese: Implications for Management Wildlife Society Bulletin Vol. 13, No. 4 (Winter, 1985), pp. 502-508.
• Howell JC. Notes on the Nesting Habits of the American Robin (Turdus migratorius L.). American Midland Naturalist. Vol. 28, No. 3 (Nov., 1942), pp. 529-603.
• FARNER DS. Age groups and longevity in the American robin. The Wilson Bulletin, Vol. 57, No. 1 (Mar., 1945), pp. 56-74. (.pdf)
• Gowaty PA, Plissner JH. Association of male and female American robing (Turdus migratorious) during the breeding season: paternity assurance by sexual accesss or mate-guarding. (.pdf)
• Wheelwright NT. The Diet of American Robins: An Analysis of U.S. Biological Survey Records. The Auk. Vol. 103, No. 4 (Oct., 1986), pp. 710-725.
• Species Profile: American Robin (.pdf)
• Aldrich JW James FC. Ecogeographic Variation in the American Robin (Turdus migratorius). The Auk. Vol. 108, No. 2 (Apr., 1991), pp. 230-249