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American Robin

Turdus migratorius

Order:
Passeriformes
Family:
Turdidae
Sections

Appearance

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American Robin is the largest thrush in North America, with an overall length of 25 cm, and an average body mass of 77 g. The Definitive Alternate (adult) male has deep grayish to dark-brown upperparts with a blackish head, white crescents above and below eye, and white tips on outer rectrices (most eastern populations); rich rufous underparts with white undertail coverts; and a white throat, streaked with black. The bill is conspicuously yellow. The adult female is similar but the has a paler gray crown and mantle, as well as a paler breast and significantly more white on the ventrum (Rifai 2007). The throats of females are less striped, with fewer, thinner stripes covering a smaller area (Rifai 2007).

Adult plumages are similar throughout the year, but males have darker breasts, less white on the ventrum, and darker crowns in spring than in autumn (Rifai 2007). Juveniles are somewhat similar to adults, but are distinguished by black spotting on the underparts, pale spotting on the upperparts including the wing coverts, an entirely white throat, and paler head with less well defined white markings, although often with a buffy whitish supercilium (Ridgway 1907).

Most western birds are paler and duller than eastern and northwestern counterparts (see Systematics: Geographic Variation).

Similar Species

American Robin is unmistakable over most of its range, but is similar to Rufous-backed Robin (Turdus rufopalliatus); Rufous-backed Robin is common and widespread in western Mexico, and is a rare but regular nonbreeding visitor to the southwestern United States. Rufous-backed Robin is similar to a pale American Robin with cinnamon underparts and a grayish head, wings, and tail, but has a rufous wash on the back and wing coverts, no white around the eye, and a more extensively streaked throat. Where their ranges overlap, the American Robin favors higher altitudes and pines. American Robin may show a pale supercilium, usually associated with pale individuals, and these have been confused with a rare visitor to North America, the Eyebrowed Thrush (T. obscurus) of Asia, which has a sharply defined supercilium, gray throat, and olive-brown back.

Detailed Description

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Singing adult male in Definitive Basic Plumage.

© Etienne Artigau, Quebec, Canada, 24 April 2011

American Robins have 10 functional primaries (the outermost, p10, is reduced in length), 9 secondaries (including 3 tertials), and 12 rectrices. Geographic variation in appearance is slight to moderate. The following molt and plumage descriptions pertain to the widespread eastern North American subspecies, T. m. migratorius; see Systematics: Subspecies for variation in appearance of the seven recognized subspecies in North America and Mexico. No geographic or sex-specific variation in molt strategies has been reported; however, some variation in the average timing and extent of molt likely occurs with latitude of breeding, due to variable environmental and migratory constraints, day-length regimes, and breeding seasonality.

Plumages

The following is based primarily on published plumage descriptions (Dwight 1900c, Ridgway 1907, Roberts 1955, Oberholser 1974c, Cramp 1988, Clement 2000), and age-related criteria (Tyler 1949a, Pyle 1997c). Sexes show similar appearances in all plumages. Definitive Plumage is assumed at Second Basic Plumage.

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Nestling at approximately 8 days in age; note brown downy feathers on head and back, sheathed feathers on back and wing.

© Eric Cormier, Georgia, United States, 26 April 2015
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Fledgling robin. Note speckled underparts and upperparts, buffy shaft streaks and tips to great, median, and lesser secondary coverts.

© Etienne Artigau, Quebec, Canada, 3 August 2011

Natal down

Present primarily April–July, in the nest. Down on head, back, and wings. Down whitish at first, becoming creamy, then gray.

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Immature male in Formative Plumage. Note blackish head and brownish gray upperparts. Similar to Definitive Basic Plumage male, but somewhat duller brown above and with paler head. Aged by retained juvenile outer greater coverts that are browner and more worn, with pale tips.

© Evan Lipton, Massachusetts, United States, 18 April 2016
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Adult male in Definitive Basic Plumage. Note blackish head, uniform slate gray upperwing coverts with silvery edges. Male similar to female, but is blacker on the head, with darker gray upperparts and more rufous on the underparts.

© Ian Davies, Massachusetts, United States, 31 March 2010
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Immature male in Formative Plumage. Note buffy tips on retained juvenile median coverts.

© Alex Lamoreaux, Pennsylvania, United States, 21 January 2016
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Some individuls are difficult to age and sex; proceed with caution, especially in the field. The solid orange underparts and blackish head of this bird point to male, and the even, same-age wing coverts indicate an adult.

© Brian Sullivan, California, United States, 2 April 2014

Juvenile (First Basic) Plumage

Present primarily May–August. Somewhat similar to Definitive Basic Plumage but crown duller, not as black, sex for sex; forehead and crown with pale shaft streaks, becoming more rufous proximally; white eye-crescents narrower; buff to whitish supercilium often present; back feathers and scapulars often tipped with white shaft streaks; upperwing greater and median coverts with terminal wedge-shaped spots or streaks of pale rusty, buff, or whitish; white spots on outer rectrices average smaller by subspecies; chin and throat white, bordered by black submustachial stripe or series of black spots; white mustacial stripe spotted black; rest of underparts cinnamon-rufous, ochraceous tawny, or buffy ochraceous (sometimes the breast much paler, occasionally whitish), conspicuously marked with black spots on sides of throat, breast, and sides, and black bars on belly and flanks. Much individual variation in the amount of rufous on the underparts; some juveniles are as bright on the sides of the breast as in definitive basic plumage, while others have little or no rufous. Sexes alike, although males may have fewer pale shafts on the crown, larger and blacker spots on the breast, and upperparts may average darker than in females (Bartel 1987, Pyle 1997c).

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Adult male in flight.

© Jay McGowan, New York, United States, 17 March 2016
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Immature female in Formative Plumage. Note the grayish head and side of neck, and retained juvenile median coverts with pale tips.

© PMDE ESTEVES, British Columbia, Canada, 24 February 2016
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Adult female in Definitive Basic Plumage. Note gray head, uniform gray upperwing coverts. Female similar to male but is grayer on the head, with paler gray upperparts and paler rufous underparts.

© Alexia S.(wkingfisher), California, United States, 28 January 2016
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Immature female in Formative Plumage. Note the worn, retained juvenile greater and median coverts.

© Alex Lamoreaux, Pennsylvania, United States, 21 January 2016
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Females average less colorful overall, especially below. In the West, females can be particularly drab.

© Brian Sullivan, Oklahoma, United States, 23 October 2011
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Leucistic individual showing pale gray head and upperparts, paler rufous below.

© John Skene, Indiana, United States, 14 April 2016
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Leucistic individual showing nearly entirely white head and upperparts, and white underparts.

© Ian Davies, Massachusetts, United States, 19 March 2010

Formative Plumage

"First Basic" or "Basic I" plumage of Humphrey and Parkes 1959 and later authors; see revision by Howell et al. 2003. Present primarily September–August. In both sexes, Formative Plumage averages brighter than Juvenile Plumage (and lacks distinct upperpart and underpart spotting) but is duller than Definitive Basic Plumage. Similar to Definitive Basic Plumage of each sex but duller brown above and with paler head. Most reliably distinguished by molt limits among upperwing median and greater coverts, the retained juvenile outer coverts more worn, paler, and with buff to buffy white tips, contrasting with replaced formative inner coverts fresher, darker gray, and with smaller or no pale tips; 1–2 tertials sometimes replaced, contrasting with older retained juvenile tertials and secondaries; and by the retained juvenile outer primaries and rectrices that are thinner, more tapered and rounded at tip, paler brown, and relatively more worn, the white patches on the outer rectrices smaller by subspecies. Plumage differences by sex as in Definitive Basic Plumage but crown and breast duller within each sex; accurate sex determination by plumage should be performed in combination with age and subspecies (see Systematics: Geographic Variation) determination, and some Formative individuals may not be reliably sexed by plumage alone.

Definitive Basic Plumage

Present primarily September–August.

Male. Head primarily blackish, the feathers veiled broadly with pale rufous gray proximally and gray distally and laterally when fresh, overall becoming blacker in appearance with wear; supraloral streak present before eye, narrow, short, whitish to pale rufous proximally; upper eyelid (primarily on distal half) and lower eyelid bordered (broadly) by white crescent. Sides of neck and remaining upperparts slate gray becoming paler on the rump and uppertail coverts, the upper back feathers (just below nape) with blackish centers, becoming more prominent when worn. Rectrices blackish with brownish tint, the outermost rectrix (r6) broadly tipped white and narrowly edged paler on outer web, the next two adjacent rectrices (r5–r4) narrowly tipped white. Upperwing lesser and median coverts slate gray, occasionally with darker centers becoming more visible with wear; greater coverts with outer web entirely pale silvery gray, becoming palest on edge of outer web; greater and median coverts often with white tips when fresh, varying in extent individually and with wear; alula, primary coverts, and remiges brownish black, margined or edged slate gray on outer webs, the edging becoming whitish on middle portion of exposed primaries and broader on secondaries; outer web of innermost tertial entirely gray, often narrowly tipped white when fresh. Chin white; throat white streaked with black or black with variable amounts of white streaking down center; breast through lower belly rufous, becoming gray on rear flanks, and with some blackish feathers on uppermost side in front of folded wing; rufous feathers (particularly on breast and sides) usually with broad dusky to whitish margins when fresh, wearing to more uniform rufous when worn; center of lowermost belly, rear-most flanks, and undertail coverts white, the central undertail coverts spotted or streaked gray; femoral feathers white with gray bases, appearing barred gray and white; underwing coverts and axillars pale rufous. In the darkest males, the back is extensively black, rufous may extend onto the throat, and some upperwing coverts may be tipped rufous.

Female. Similar to male but paler overall, especially on head, the crown largely grayish due to broader feather margins; upperparts average more brownish (less gray); breast and remainder of underparts paler rufous due to broader whitish feather margins in fresh or worn plumage. Accurate sex determination by plumage best accomplished in combination with subspecies and age determination (see Formative Plumage, above).

Definitive Basic Plumage separated from Formative Plumage by having wing and tail feathers uniform in quality and freshness: upperwing coverts, tertials, and inner secondaries uniform in wear, fresher, with narrower and more-distinct pale tips if present; basic outer primaries and rectrices broader, more squared and truncate, darker, and relatively fresher, the white patches to the outer rectrices averaging larger by subspecies (Pyle 1997c).

Aberrant plumages

Albinism and melanism have both been reported frequently (Tyler 1949a, Pitzrick 1983, Rogge and Rogge 1984, Isaacs 1985, Laird 1987, Johnson 1988d). Leucism is also known to occur (e.g., Academy of Natural Sciences of Drexel University, specimen no. 35218).

Molts

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Figure 2. Annual cycle of molt, breeding, and migration.

Thick lines show peak activity and thin lines show off-peak.

General

Molt and plumage terminology used here follows Humphrey and Parkes 1959, as modified by Howell et al. 2003 and Howell et al. 2004. American Robin exhibits a Complex Basic Strategy (cf. Howell et al. 2003, Howell 2010b), including complete prebasic molts and a partial preformative molt but no prealternate molts (Dwight 1900c; Oberholser 1974c; Cramp 1988; Pyle 1997c; Pyle 1997d; Figure 2).

Prejuvenile (First Prebasic) Molt

Complete, primarily May–July in North America, in the nest. In newly hatched chicks, capital and alar feather tracts show dark feathers through skin. Little information is available on the timing or sequence of pennaceous feather irruption and development. Duration of Prejuvenile Molt among individuals probably lasts 9–12 d, and is presumably completed or near-completed by fledging at day 10–16.

Preformative Molt

"First Prebasic" or "Prebasic I" Molt of Humphrey and Parkes 1959 and some later authors; see revision by Howell et al. 2003. Partial, primarily July–October (Figure 2), on or near the breeding grounds. Includes some to all of the upperwing median coverts, no (in 10–15% of individuals) to 9 inner greater coverts, and sometimes (20–25% of individuals) 1–2 tertials, but no other secondaries, primaries, primary coverts, or rectrices.

Definitive Prebasic Molt

Complete, primarily July–September (Figure 2), on or near breeding grounds, although more study is needed on the relationship between breeding territories and molting grounds. Primaries are replaced distally (p1 to p10); secondaries likely replaced proximally from s1 and proximally and distally from the central or innermost tertial (s8 or s9), as typical of passerines; and rectrices probably replaced distally (r1 to r6) on each side of tail, with some variation in sequence possible.

Bare Parts

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Close-up showing bright yellow bill seen on some individuals.

© John Hanna, Alaska, United States, 14 May 2016

Bill and gape

Mouth rich yellow and gape flanges pale yellow in nestlings; mouth lining light cadmium. In adults, bill is yellow, often with darker tip; gape also yellow.

Iris

Dark brown.

Legs and feet

Brown.

Linear Measurements

Throughout its range, male American Robins are larger than females in the length of the wing, tail, and middle toe, but not in the length or depth of the bill. The following measurements are from specimens in museums collected during the breeding season (Aldrich and James 1991). Sample sizes range from 10 to 50 unless otherwise noted.

Bill length and depth

Median bill length in adult males (culmen, from the depression between cranium and maxilla to tip of maxilla) ranges from 22.4 mm in boreal forests of Canada and Alaska and 22.6 mm in coastal plain of Gulf of Mexico to 24.6 mm in Wyoming Basin and 26.0 mm in Baja California. Median maxilla height (depth of upper bill at distal end of depression around nostril) ranges from 4.3 to 4.8 mm, <0.5 mm continent wide. Sexes not significantly different in either measurement.

Wing length

Median wing length in adult males ranges from 124.7 mm in the southeastern U.S. and from New York to Wisconsin to 135.7 mm in the Oregon and Montana Rockies. Median wing length in females has a similar pattern of geographic variation but is significantly shorter: median wing length 119.1 mm in the Gulf coastal plain and 130.9 mm in eastern Washington and western Idaho (n = 6). In Kentucky mean wing length for males is 130.7 mm ± 3.8 SD (n = 72) and for females is 123.6 mm ± 3.7 SD (n = 75; ENV).

Tarsus length

Median tarsal length in males ranges from 33.0 mm in coastal plain to 35.5 mm in Wyoming Basin (n = 4) and 35.6 mm in Newfoundland. Median tarsal length in females ranges from 33.0 mm in the Southern Appalachians to 35.3 mm in the northern Rocky Mountains.

Longest toe length

Median middle toe length in males ranges from 19.7 mm in mainland Mexico to 22.7 mm in the northern Wyoming Basin (n = 4). Females range from 19.7 mm in coastal plain to 21.8 mm (n = 3) in the Brooks Range of northern Alaska.

Mass

In Pennsylvania, mean body mass was 77.3 g ± 0.36 SD (n = 401) for males and females throughout year (Clench and Leberman 1978). In Kentucky, body mass of males: 74.9 g ± 4.4 SD (n = 72); of females: 75.5 g ± 5.0 SD (n = 75; ENV).

During the breeding season in Enterprise, Oregon, mean body mass was 84.8 g ± 1.5 SE for males (n = 4) and 75.0 g ± 2.4 SE for females (n = 2; RS). In Ithaca, New York, average female body mass in winter, 83.6 g ± 6.4 SD (n = 26), 2.6 g less than average for males in winter; average mass for 21 males in breeding season, 77.4 g (Howell 1942).

Recommended Citation

Vanderhoff, Natasha, Peter Pyle, Michael A. Patten, Rex Sallabanks and Frances C. James. 2016. American Robin (Turdus migratorius), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/bna.462