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American Robin

Turdus migratorius

Order:
Passeriformes
Family:
Turdidae
Sections

Breeding

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Phenology

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Adult gathering nest material.

© David Wade, Colorado, United States, 21 April 2016
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Figure 2. Annual cycle of molt, breeding, and migration.

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

Pair formation

Males usually arrive at breeding sites a few days before females (Howell 1942). When individuals arrive, testes contain developing spermatocytes and ovarian follicles are enlarged (Kemper and Taylor 1981). Mates appear to be chosen at least partially based on plumage (See Behavior: Sexual Behavior; also Rowe and Weatherhead 2011).

Nest-building

Female constructs the nest, usually in 5–7 d for the first nests of the season, but sometimes taking as long as 2 wk, especially if it is too wet or so dry that she has to wait for rain to produce mud. If nest is destroyed, female can build a new nest in 2–3 d (Kendeigh 1952, Young 1955). Later nests can be built in 1 d, but this is unusual (Howell 1942). Testes by then contain developing and/or mature sperm (Kemper and Taylor 1981).

First/later broods

Figure 2. Egg-laying dates (of first egg/clutch) in Madison, WI: 12 Apr–22 Jul (Young 1955); Ithaca, NY: 6 Apr–24 Jul (Howell 1942); n. Maine: 10 May–6 Jul (Knupp et al. 1977); Churchill, Manitoba: 28 May–26 Jun (J. V. Briskie, unpubl. data); Pacific Northwest (Idaho, Oregon, Washington, Montana): 5 May–20 Jul (RS). Peak egg-laying dates (50% of nests, n = 19) for Pacific Northwest 5 Jun–4 Jul (RS); peak egg-laying dates not available for other regions.

In Ithaca, NY, female lays 1 egg/d, for 3 or more commonly 4 d. Female incubates eggs for approximately 13 d (range 12 to 14) after laying the last egg (Martin 1973e, Howell 1942), although may begin before laying the last egg (see Incubation, below). Hatching takes 24 h, and nestlings usually spend 13 d in the nest before fledging. Second brood can fledge 5 wk after the first. Most cases of third nests in a season follow nest failure, but robins regularly rear 2 broods/season; 41% of 39 pairs remained on the same territory for the second brood (Young 1951).

According to data for > 8,500 nests from the Cornell Laboratory of Ornithology Nest Record Card Program, most robins begin to feed their first brood in the last 10 d of Apr in the Southeast, mid-May in New England, and late May and early Jun in both the Rocky Mtns. and central Alaska (James and Shugart 1974). If day length were the single determinant, birds would be expected to nest later at higher latitudes. In general, they do so in the eastern states, where the breeding season is delayed 3 d/degree of increasing latitude (see also Kessel 1953b for the European Starling in the same area), but robins breed in Colorado Springs, CO, at 39°N latitude at the same time as those in Fairbanks, AK, at 65°N latitude. Nor can mean daily temperature be the sole determinant, because nesting begins at higher temperatures in the western states than in the eastern ones and at successively lower temperatures farther north in the eastern states: 27°C for central Colorado, 16°C for southeastern states, 13–16°C for northeastern states and the Great Lakes region.

As with size variation, a combination of variables, including temperature and humidity, predicts nesting time better than does either temperature or latitude. This combination is undoubtedly a correlate of more direct cues to the birds, such as the availability of soft invertebrates near the surface of the soil. The model of James and Shugart (James and Shugart 1974) predicts that robins should nest earlier in the Maritime Provinces of Canada than inland in Maine, which is farther south, and they do (Howard 1967). However, the model does not predict nest dates in British Columbia well (Kemper and Taylor 1981).

Torti and Dunn (Torti and Dunn 2005) examined 50 yr of nesting data to determine the effects of climate change on clutch initiation date and clutch size. They found no overall significant effect of temperature; however, the mean laying date shifted slightly later in the season in more recent years, and robins breeding at high elevations tend to breed later.

Length of period when a local population of robins has young in the nest (the period that contains 90% of nests with young) varies from 80 d in the eastern and central states to 60 d in New England, 50 d in the western mountains, and 27 d in central Alaska (James and Shugart 1974). First nests are not completed until June in Newfoundland and Fort Yukon, AK (Tyler 1949a).

At the peak of egg-laying (first brood), males testes are fully spermatogenic and females have enlarging follicles and/or have ovulated at least once. In sw. British Columbia, testes reached maximum mass throughout May; fully ripe ovarian follicles were observed most frequently in early May. Initial declines in testicular weight began in early June, although testes were fully spermatogenic throughout the month. By the latter half of June, ovulatory activity in females rapidly declined. In July, gonads of both sexes became inactive (Kemper and Taylor 1981). However, there are several records of robins nesting in fall and winter (Sep: Nebraska, Tennessee, Ohio, Michigan, Illinois, Alaska, and Québec; Oct: Massachusetts and Manitoba; Nov: West Virginia; Jan: Ohio; Gardali and White 2003). Although these constitute a small percentage of all nest records examined (< 0.1%), recent research in Missouri indicates that the majority of Oct nests were successful (8 of 10 nests fledged young; Gardali and White 2003).

Nest Site

Selection process

Male may visit the nest site before nest construction and bring nesting material to his mate, but the female selects the site and builds the nest (Kendeigh 1952).

Microhabitat

In NY State, first nests of the season are likely to be low in a protected evergreen tree, later ones higher in a deciduous tree; of 244 nests in Ithaca, NY, half were < 3 m high (Howell 1942).

Following data (range, n) are from the Pacific Northwest (Idaho, Oregon, Washington, Montana; RS): mean nest height, 3.6 m ± 0.2 SE (0.5–32.0, 257 nests); mean height of nest trees, 7.9 m ± 0.5 SE (0.7–43, 253 nest trees); mean diameter at breast height of nest trees, 12.7 cm ± 0.9 SE (0.8–70, 248 nest trees); mean number of branches supporting nests, 2.8 ± 0.1 SE (1–6, 244 nests); mean diameter of supporting branches, 1.7 cm ± 0.1 SE (0.8–15.2, 244 nests); compass direction of nests around tree centers not significantly different from random with mean distance from main trunk 0.4 m ± 0.1 SE (0–6, 246 nests); mean foliage cover directly over nest 68.7% ± 2.3 SE (0–100%, 208 nests); and mean foliage side cover estimated from all 4 cardinal directions 50.8% ± 2.1 (0–100%, 234 nests).

In riparian habitats of central Nevada's Toiyabe Mtns., robins build nests in semi-open habitats with little vegetation; prefer to nest in single-leaf pinyon (Pinus monophylla) over quaking aspen (Populus tremuloides), despite higher abundance of aspen (Warkentin et al. 2003). Moreover, they do not switch from evergreen to deciduous trees later in the season as seen in New York. Nests also show specific orientation (south, southeastern or eastern) that may allow robins to take advantage of warm morning sun and avoid hot afternoon sun (Warkentin et al. 2003).

Site characteristics

Can be from ground to tree tops but usually saddled on a firm support and sheltered from rain, often just below the layer with the largest volume of foliage (Savard and Falls 1981). Nests in western prairies may be on the ground or in thickets (Mearns 1879); in British Columbia, in the broken tops of tree stumps and in road banks (Campbell et al. 1997b); in Alaska on buildings, on cliffs north of the tree limit, and in many areas on human-made structures such as roof gutters (Howell 1942).

Mean forest canopy cover at 235 nest locations in the Pacific Northwest: 27.2% ± 2.3 SE (range 0–100%; RS). No relationships with slope or aspect. In the interior Pacific Northwest (Idaho, w. Montana, ne. Oregon), nests found in 19 different plant species, including conifers and deciduous shrubs; most notably, grand fir (21%), Douglas-fir (19%), ponderosa pine (12%), black hawthorn (Crataegus douglasii; 10%), and Engelmann spruce (Picea engelmannii; 8%). In sw. Washington, nests found in 6 plant species: Douglas-fir (69%), western hemlock (13%), red alder (Alnus rubra; 9%), balsam poplar (Populus balsamifera; 3%), vine maple (Acer circinatum; 3%), and big-leaf maple (Acer macrophyllum; 3%; RS). In subalpine fir forests of the Blue Mtns., ne. Oregon, following severe wildfire, robins frequently nest directly on the top of exposed broken-top snags (RS).

Nest

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Nests typically are bulky with a substantial amount of mud in the nest wall, an unkempt grassy exterior, and lined on the inside with finer materials.

© Aaron Boone, Wisconsin, United States, 3 May 2016
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American Robin nest with prominent mud wall, lined with finer materials.

© Deb Pritchard, Wisconsin, United States, 27 April 2016
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Figure 6. Nest and eggs of the American Robin.

Taken from the Illustrations of the Nests and Eggs of Ohio, 1879-1886. Drawings by G. E. Jones, N. E. Jones, and E. J. Schultz.

Construction process and composition matter

Working from inside, female constructs the outer wall with dead grass and twigs, pressing from inside with the wrist of her wing (Howe 1898 cited in Tyler 1949a), sometimes adding white paper, feathers, rootlets, or moss to outside; then carries mud from worm castings in bill and kneads it by rotating body in the hollow of the cup (Howell 1942). Finally, female lines the nest with fine pieces of dead grass. Dry weight of a nest in Illinois was 205 g, of which 35% was originally mud (Klimstra and Stieglitz 1957).

Robins nesting in temperate rain forests of the Pacific Northwest often put the nest on a platform of twigs (Tyler 1949a). In Canada, nests from northern sites are larger and heavier with thicker nest walls and a deeper interior cup than farther south (Crossman et al. 2011). Nests in city parks in Kentucky often contain plastic bags and other man-made materials (ENV).

Dimensions

Data from 5 geographic regions provided in Table 2 .

Microclimate

No data.

Maintenance or reuse of nest

Once constructed, nest is not maintained and may be destroyed by wind and rain. Old nests may be reused with or without a new lining (Howell 1942); a new nest may be built on top of an old one on a man-made structure, but more commonly a new nest is constructed for each brood. In Kentucky new nests may be constructed in the same tree in separate years (ENV); in Kansas, an individual was documented reusing the same nest site in consecutive years as well (Applegate et al. 2000). In New Brunswick, an old robin nest was reused by a red squirrel (Tamiasciurus hudsonicus) for caching truffles (Vernes and Poirier 2007). Eastern Kingbirds (Tyrannus tyrannus) in se. Oregon frequently reuse robin nests (Cancellieri and Murphy 2013).

Nonbreeding nests

No evidence of nonbreeding nests.

Eggs

Shape

Subelliptical to oval.

Size

In Ithaca, NY, mean length × breadth = 28.4 × 20.7 mm (n = 30; Howell 1942); in s. Baja California, 30.3 × 20.5 (n = 19; Tyler 1949a); in Churchill, Manitoba, 29.9 × 21.4 (n = 22; J. V. Briskie unpubl. data). Runt eggs (substantially smaller) often occur.

Mass

Average fresh weight of 30 eggs in Ithaca, NY: 6.3 g. Estimated weight for adult females without reproductive tissue is 74.8 g, thus 1 egg = 8.4% of adult female mass (Howell 1942). In n. Maine, mean weight of 18 eggs also 6.3 g (Knupp et al. 1977). In Ohio, reproductive vigor of female and her egg quality change seasonally and are optimal when mean monthly temperature is 15.5–21°C. On either side of this environmental window, the female lays smaller and lighter-weight eggs (Kendeigh 1942).

In Nevada, the effect of cattle grazing and anthropogenic alterations to riparian habitat on egg mass was examined. Mean egg mass was not significantly different among three canyons in the Toiyabe Mtns., but the most degraded canyon site had eggs with the lowest mean weight (6.6 g, n = 13), as compared to intermediate (6.9 g, n = 6) and least degraded sites (7.2 g, n =10, Warkentin et al. 2004a).

Color

Darker eggs are Nile blue and lighter ones deep bluish glaucous, using Ridgway's (Ridgway 1912) color scheme; rarely spotted or white. Typically sky blue and unmarked, can become glossy with incubation. English and Montgomerie (English and Montgomerie 2011) tested whether intensity of egg color was a signal of female quality, predicting more vividly colored eggs garnered more care from males. Provisioning was significantly higher in vivid egg treatments and males that saw vivid eggs fed 3 d-old nestlings three times as much as those that saw paler eggs (English and Montgomerie 2011).

Surface texture

Texture changes from smooth to leathery during incubation (Howell 1942).

Eggshell thickness

No information on thickness. Following data are empty shell weights based on clutch means; ranges are for individual eggs. T. m. migratorius: 0.36 g (range 0.23–0.46), n = 24 clutches (91 eggs); T. m. achrusterus: 0.35 g (range 0.26–0.45), n = 24 (94); T. m. caurinus: 0.38 g (range 0.30–0.43), n = 24 (19); T. m. propinquus: 0.36 g (range 0.26–0.45), n = 24 (84; Western Foundation of Vertebrate Zoology).

Clutch size

See Demography and Populations: Measures of Breeding Activity.

Egg-laying

Unusual among songbirds in laying eggs in late morning, or even early afternoon, rather than around sunrise (Weatherhead et al. 1991a, Scott 1993e and references therein). Females able to remain active immediately before egg-laying and are therefore not restricted to laying early in the morning. May nevertheless use sunrise as a cue to time egg-laying, as egg-laying times were significantly correlated with the time of sunrise in robins studied by Weatherhead et al. (Weatherhead et al. 1991a).

First egg laid 3–4 d after nest completion (range 1–8 d, n = 8; Kendeigh 1952); 1 egg/d, late in the morning (average of 10:00 for 7 nests [Howell 1942]; average of 11:32 for 37 eggs [Weatherhead et al. 1991a]). Single eggs not replaced if lost. Male remains close to the female and copulates daily until the clutch is complete.

Incubation

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Incubating American Robin.

© Kent Warner, New York, United States, 20 April 2016

Incubation patch

As is typical for passerines during the breeding season, female has a vascularized brood patch on her abdomen from which her body heat is transferred to eggs during incubation.

Onset of broodiness and incubation in relation to laying

Incubation may begin after the second egg is laid (Schantz 1939), perhaps by application of only partial heat (Kendeigh 1952). Temperature monitoring of nests in the Sierra Nevada Mtns. of California confirm partial heating; female sits on the nest during the night after the first egg is laid, but maintains a minimal temperature, and full incubation does not begin until the second egg is laid (Morton and Pereyra 2010).

Daytime nest attentiveness is interrupted only by foraging bouts; on the first day of egg-laying female was away from the nest 90% of the time, compared to 0% on day 4 when the clutch was complete (Morton and Pereyra 2010). In Illinois, while over half of 128 females (57.8 %) began incubation before clutch completion, some waited until the day of clutch completion (22.7%) or even the day after clutch completion (19.5%; Rowe and Weatherhead 2009). Females delaying incubation nested earlier and although their eggs took longer to hatch, the numbers of young hatched and fledged did not differ from those of females incubating earlier. If predation is low, delayed incubation may allow for more foraging time (and energy) for the female, as well as providing a benefit for nestlings whose hatching may coincide with the availability of more resources (Rowe and Weatherhead 2009).

Incubation period

Period from laying of last egg to hatching of last egg is reported variously as 12–13 d (Kendeigh 1952) and 12–14 d (Howell 1942).

Parental behavior

Male may bring food to incubating female, but this is unusual (Kendeigh 1952). Female incubates with eggs against her brood patch for bouts of about 40 min, stands on rim and turns eggs, flies off for a break (Howell 1942). In Ohio, incubating female leaves nest 25 min before sunrise; spends 75–80% of daytime incubating early nests when temperatures are cool, 65–70% in Jun and Jul, averaging 32 attentive periods/d (Kendeigh 1952).

Hardiness of eggs

No information.

Hatching

Preliminary events and vocalizations

Young not known to vocalize before hatching.

Shell-breaking and emergence

Eggs tend to hatch in their order of laying over a period of 2–3 d (Kendeigh 1952). Single chick takes about 24 h to hatch, pipping the egg with its egg tooth by making a ring of fractures above the greatest circumference of the egg (Howell 1942).

Parental assistance and disposal of eggshells

Female carries the eggshell off and may eat it (Howell 1942).

Young Birds

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At approximately 8 days-old, nestling has downy feathers on head and back, and sheathed feathers on back and wings.

© Eric Cormier, Georgia, United States, 26 April 2015

Condition at hatching

Hatchlings are colorful, with translucent Baryta yellow skin, through which can be seen a greenish gall bladder, purplish-red liver, and orange yolk; bill orange-pink, mouth lining light cadmium (Howell 1942). Down whitish at first, becoming creamy, then gray; ventral surface is bare; white egg tooth may be retained until fledging. Average wing length of 9 hatchlings in Ithaca, NY, 8.8 mm (range 7.5–9.5), tarsus length 9.0 (range 7.5–9.5). Mass at hatching 5.5 g (range 4.1–6.7). Eyes open on day 5 (Howell 1942).

Growth and development

Some sectors of nests receive more feedings than others because parents generally arrive at a predictable location on the nest rim; nestlings therefore compete with one another for food by “jockeying” for position within nests (McRae et al. 1993). Degree of nestling movement is positively correlated with variation in the predictability of parental arrival locations on the nest rim. Nestlings move more in broods suffering brood reduction (McRae et al. 1993).

Robin nestlings compete by begging. Parents are more likely to feed a nestling that starts begging earlier, extends its neck higher, and holds its beak closer to the parent's beak. Nestlings prevented from feeding by being removed from nests for 1 or 3 h increased their begging intensity relative to nest-mates (Smith and Montgomerie 1991a). Begging intensity also depends on the begging intensity of siblings. Presumably, therefore, increased begging influences the probability of receiving food (Smith and Montgomerie 1991a).

Parental Care

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Adult robin tending to nestlings.

© Paul Bourdin, New York, United States, 13 May 2016

Brooding

Female broods young for the first few days until they develop homeothermy and protects them from inclement weather, but does not usually remain on the nest at night after the first week (Kendeigh 1952).

Feeding

Young are fed regurgitated food for the first 4 d after hatching (Tyler 1949a). Food consists of soft invertebrates such as beetle grubs and parts of earthworms, but may be 30% plant material (Howell 1942). Older young can regurgitate pits of cherries. Both parents feed nestlings, delivering 6–7 feedings/h, each one to a single nestling, so that each nestling gets 35–40 feedings/d (Kendeigh 1952); parents can bring about 200 g of food/d to the nest, or 1.45 kg of food in 14 d (Hamilton 1935). In broods where males provide more care than females, largest chick is fed primarily by the male, smallest chick primarily by the female; when male provides less care than female, opposite pattern exists (Slagsvold 1997a). Feeding grounds may be shared with other adult pairs of birds (Howell 1942).

Nest sanitation

With each feeding, nestling produces a fecal sac, which is consumed by the parent when young are <1 wk old. As nestlings get older, a smaller proportion of fecal sacs are eaten and more are carried away from the nest (> 30.5 m; Howell 1942)—perhaps because the cost to the parent of consuming fecal sacs increases as the size and number of sacs produced by nestlings increase (Hurd et al. 1991).

Carrying of young

None.

Cooperative Breeding

None.

Brood Parasitism

Recognizes and rejects Brown-headed Cowbird (Molothrus ater) eggs, puncturing them and throwing them out of the nest (Friedmann 1929), even north of the geographic range of the cowbird (Briskie et al. 1992). A few cases are known in which a pair of robins reared a cowbird (Lowther 1981, Wolfe 1994).

In Colorado, robins rejected all cowbird egg models placed in nests, but had similar reactions to models of female cowbirds and models of house sparrows (Cruz and Cooper 2001). Underwood and Sealy (Underwood and Sealy 2006) experimentally examined the role of cowbirds' egg shape on nest rejection in robins by adding a variety of differently shaped objects to robin nests. Object shape was a significant predictor of rejection; robins more readily rejected odd-shaped objects such as cubes and cylinders vs. egg-shaped objects (pointed, rounded, spherical). Among egg-shaped objects, a higher proportion of pointed eggs were ejected; rounded and sphere eggs were ejected at similar proportions as control eggs (Underwood and Sealy 2006). Recent work suggests that the larger bill size of robins allows them to grasp-eject (grasping the entire width of the egg with their beaks) most cowbird eggs, rather than puncturing them. In Manitoba, video-recorded robins grasp-ejected all cowbird eggs presented to the nest (12 out of 12; Rasmussen et al. 2009). Robins will switch from grasp-ejection to pinch-ejection (grasping the end of the egg with its bill) when presented with larger egg models (Rasmussen et al. 2010).

Intraspecific brood amalgamation is known to occur occasionally when 2 females share a nest simultaneously and produce 6–8 eggs (Howell 1942). Although robins sometimes lay eggs in the nests of other species, they are generally not raised -- although House Wrens and other species have been raised by robins in a few robin nests (Howell 1942). One record in Iowa of robin and Northern Cardinal (Cardinalis cardinalis) using the same nest at the same time; both laid eggs and both brooded eggs, but once the robins hatched the cardinals left the nest and their eggs were abandoned (Govoni et al. 2009).

Fledgling Stage

Departure From Nest

Chicks begin to lose weight on day 9 or 10 of development, fledge on about day 13 (range 9–16; Howell 1942). Nestmates leave the nest within a 24-h period, wander off a short distance, and are followed and fed by parents (Weatherhead and McCrae 1990). When the brood is partially fledged, young remaining in the nest are fed primarily by the female (Slagsvold 1997b).

Growth: Mass, Proportions, Structures

No data.

Association With Parents

After fledging of the complete brood, first the female and then the male follow the young and provide food as they wander about within 150 m of the nest for at least 3 wk (Weatherhead and McCrae 1990). When a female is on a second nest, the male may take fledged young to a communal roost at night (Brewster 1906 cited in Tyler 1949a, Hirth et al. 1969).

Ability To Get Around, Feed, And Care For Self

At fledging, young birds cannot maintain level flight and spend next 10–15 d in cover before becoming independent (Young 1955). At 13 d of age, captive hand-reared nestlings develop a distinct period of high activity at dusk, referred to by Eiserer (Eiserer 1979, Eiserer 1980a) as “roost-time restlessness.” At the age of 4 wk, juveniles are able to manage independently.

Immature Stage

Young remain on breeding grounds for up to 4 mo. In Sep, after adults have undergone annual molt in Jul and Aug (Wheelwright 1986), young gather in mixed flocks with adults (Young 1955), following them to feeding areas with fruit, loafing areas, and roosts (Hirth et al. 1969), and eventually migrating with them to wintering grounds.

Recommended Citation

Vanderhoff, N., P. Pyle, M. A. Patten, R. Sallabanks, and F. 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, NY, USA. https://doi.org/10.2173/bna.462