American Redstart

Setophaga ruticilla



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Figure 3. Annual cycle of molt, breeding, and migration of the American Redstart.

Figure shows data for American Redstart in the northeastern U.S. Thick lines show peak activity, thin lines off-peak.

Representative breeding habitat of the American Redstart.

A northern hardwood forest at Hubbard Brook in New Hampshire. Dominant trees are sugar maple, American beech and yellow birch, with an understory of shrubs, ferns, and tree seedlings and saplings.

© Sara Kaiser, New Hampshire, United States, 25 May 2012
Figure 7. Illustration of nest and eggs of American Redstart.

Taken from the Illustrations of the Nests and Eggs of Ohio, 1879–1886. Drawings by Miss Genevieve Estelle Jones, Mrs. N. E. Jones and Miss Eliza J. Schultz.

American Redstart clutch.

Size and color of eggs vary; some eggs are nearly whitish, others heavily speckled. Greene County, Pennsylvania, 23 May. Ruler is in cm; photographer Rene Corado.

Female American Redstart brooding chicks on a nest.

Nest is in an American beech sapling. Nest includes spider silk and egg cases, and bark strips from yellow birch and probably white ash.

© Thomas Sherry, New Hampshire, United States, 4 July 1982
Female American Redstart on nest.

Nest is tightly woven open cup, fitted to branches, constructed of variety of natural small fibers. Female alone incubates.

© Charles Henrikson, Wisconsin, United States, 10 June 2016
Male American Redstart at nest.

Both sexes feed chicks, each parent typically making 50% of food-provisioning trips.

© Kelly Preheim, South Dakota, United States, 6 July 2016
American Redstart hatchlings in nest.

Eyes open to narrow slits at 3 days of age, at same time wing-feather papillae appear. Flight-feathers break through sheathes at Day 6, and Juvenile plumage is worn by Day 8.

© Jim Lind, Minnesota, United States, 3 July 2009
Adult female American Redstart with fledgling.

Fledglings typically have substantial subcutaneous fat at time of fledging and weigh about as much as adults. Wings and tail are about half grown at time of fledging.

© Simon Boivin, Quebec, Canada, 4 August 2015
Adult female American Redstart with fledgling.

Attending adults provide most food during first week after fledging, and continue to feed chicks for up to 3 wk. Parents usually divide brood after chicks have left nest; thus each parent feeds only particular fledglings.

© Steeve R. Baker, Quebec, Canada, 10 July 2016
Adult male American Redstart with 2 redstart and 1 Brown-headed Cowbird nestlings (larger chick on right).

The Brown-headed Cowbird can successfully parasitize the American Redstart (e.g., redstarts accept cowbird eggs at some nests and feed cowbird fledglings).

© Melody Walsh, Wisconsin, United States, 21 June 2016
Adult female American Redstart feeding young Brown-headed Cowbird.

By the time Brown-headed Cowbird young are near independence, they may be much larger and heavier than redstart foster parents.

© Mark Benson, Wisconsin, United States, 30 June 2016


Pair Formation

Occurs within hours to a day or so after female arrives at breeding site (Ficken 1963a, TWS), which tends to be a week or so after arrival of older males (mid-May in central New Hampshire).


Begins within few days of arrival of female at breeding grounds, if weather is favorable, but may be delayed by cold or rainy weather (TWS). Many nest starts are abandoned early in season (last week of May in New Hampshire; TWS), presumably because of weather (e.g., rain or wind removing some material from nest site). Female builds new nests relatively quickly later in the season (e.g., in response to starvation of nestlings or nest predation), in part because it often uses material from old nest (TWS).

First/Only Brood Per Season

Figure 3. Begins nesting mid-late April in southernmost breeding range (Louisiana; TWS), late May-early June in New Hampshire. Frequently renests if unsuccessful in earlier nesting attempt; females build up to 6 different nests in a season in effort to fledge a brood (McKellar et al. 2014).

Egg dates 12 May–6 June in Alabama (n = 11; Imhof 1976); 19 May to first week of July in Ohio (Peterjohn 2001); 20 May–13 July in Minnesota (Robbins 1991); 27 May–27 July in Ontario (n = 240; Peck and James 1987). In Hubbard Brook Experimental Forest, New Hampshire, earliest egg date 20 May (back-calculated 22 d from 11 June fledge date) but 24 May is more typical; latest egg date 16 July, and latest fledge date 25 July (TWS).

Earliest nesting dates in North America recorded in Louisiana, with clutch completion dates of 1, 3, 6, 7, 10, 11, and 14 May (TWS, unpublished data).

Second/Later Brood Per Season

Not reported, although might be expected in the southern U.S., where breeding season may be longer than higher latitudes.

Nest Site

Selection Process

Female plays major role in selection of nest site, but male shows female potential sites as part of early courtship (see Behavior: Sexual Behavior). Before selecting site, female tries out many potential sites by settling down into them with her breast and moving around (Ficken 1963a, Ficken 1964). Site characteristics used in selection process not studied rigorously, but several may be inferred:

(1) Protection from predators: Nests constructed within yellow-birch sites at Hubbard Brook, New Hampshire, were well camouflaged and significantly less likely to be depredated than other nests (J. P. Crews and TWS, unpublished data). See also Behavior: Predation.

(2) Ease of adhering nest material (especially cobwebs and small bits of birch bark in New Hampshire) to substrate, as suggested by underuse of striped maple (Acer pensylvanicum) trees for nesting, which are too smooth for nest material to stick, and have a branching pattern that may provide inappropriate nest sites (TWS); several females abandoned attempts to build nest in this tree species, in one case after trying for > 1 wk (TWS). May also avoid aspens (Populus spp.) and some conifers because of smooth bark or inappropriate architecture (Morris and Lemon 1988a).

(3) Stability of site and protection from elements: Most nests are relatively well protected from sun and wind by placement within well-foliated sites or beneath overhanging leaves or stems. See also Site Characteristics.


Typical nest in the northern U.S. is usually surrounded by foliage within well-vegetated sites, generally against the main trunk of live (rarely dead) tree or in leafy woody shrub, essentially always supported by 3 more-or-less vertical stems for attachment of nest material (Ficken 1964). Generally next to central vertical trunk, but occasionally saddled on horizontal branch up to 2 m from main trunk if vertical attachment stems are present (Ficken 1964, Peck and James 1987, TWS). Nests in Ontario were built in 28 species of shrubs and saplings, occasionally in mature trees; 97% were in live plants and 92% were in deciduous rather than coniferous plants (Peck and James 1987). Most frequently chosen plant species there, in decreasing order of use, were maple (Acer spp.), birch (Betula spp.), ash (Fraxinus spp.), hawthorn (Crataegus spp.), alder, and northern white-cedar (Thuja occidentalis). In a study in New Brunswick (Morris and Lemon 1988a), most nests (n = 208) were in speckled alder (Alnus rugosa; 30.7%) and paper birch (Betula papyrifera; 22.1%), both of which are abundant trees there, but nests were also built in northern white-cedar (11%), cherry (Prunus spp.; 8.7%), and hawthorn (4.8%), among others. In Alberta, 246 nests were built in alder species (primarily Alnus tenuifolia and A. crispa; 39%), balsam poplar (Populus balsamifera; 26.3%), Bebb’s willow (Salix bebbiana; 21.2%), paper birch (8.9%), and quaking aspen (Populus tremuloides; 1.9%; M.-A. Villard and S. Hannon, personal communication). Vines are rarely used (Ficken 1964), but see Site Characteristics.

In studies within the heavily forested northern hardwoods of Hubbard Brook, New Hampshire, favored trees for nests (n = 623) were sugar maple (Acer saccharum; 37.8%), yellow birch (31.0%), and American beech (Fagus grandifolia; 28.4%; TWS and RTH). Other plants used were hobblebush (Viburnum alnifolium; 1.6%) and striped maple (1.0%). Nests were never in white ash (Fraxinus americana) or any of the conifers (spruce [Picea], fir [Abies], hemlock [Tsuga]) at Hubbard Brook, and were rarely found in paper birch, unlike in New Brunswick, where this tree species is more abundant (R. E. Lemon, personal communication).

Site Characteristics

At Hubbard Brook, New Hampshire, nest height averaged 8.2 m ± 6.43 SD (range 1–28 m; n = 640), but frequency distribution of nests was not normal; strong mode at 1.5–3 m, and second shallow mode stretched from 10 to 20 m above ground. This nonnormal frequency distribution of nest heights probably results from abundance of preferred high nest sites at Hubbard Brook: Nests were higher when built in yellow birch (median height 15 m) than in other species (median heights 1–4 m), but nests higher than 10 m were built regularly in trees other than yellow birch as well. Most other studies describe American Redstart nest sites as lower than at Hubbard Brook: 1.25-6 m (Baker 1944a), 1–8 m (Sturm 1945), 1–6 m (Bent 1953b), 1–10 m (Ficken 1964), 0.3–15 m (average 1.8–3.7 m; Peck and James 1987), 2.2–5.3 m depending on plant species (Morris and Lemon 1988a), average of 3.38 m ± 1.68 SD (range 0.61–12 m, n = 246; M.-A. Villard and S. Hannon, unpublished data), and 2.74 ± 1.30 m in Ontario (Falk et al. 2011). Some of these height estimates may be biased toward lower, easier-to-find nests. Morris and Lemon 1988a reported a reasonable fit of their nest heights to a log-normal frequency distribution, skewed toward lower nests.

In some areas, especially western and southern parts of breeding range, often builds nest in vegetation near or over water (e.g., in bottomlands, wooded swamps, and along rivers and streams; Mengel 1965b, Peterjohn 1989b, Robbins 1991, Semenchuk 1992, Gilligan et al. 1994). Also nests in swamps or along streams (e.g., in alder, eastern white-cedar, and red maple [Acer rubrum]) in eastern and northern parts of breeding range, but is not limited to wet sites there (Ficken 1964, Peck and James 1987, Morris and Lemon 1988a, TWS). In general, tends to nest low within small trees, saplings, and occasionally shrubs that provide some cover, but uses variety of heights and plant species, depending on local circumstances.

Comparison of nest and nest microhabitat characteristics with latitude in four sites (Louisiana, Maryland, Ontario, and Alberta) reveals a variety of differences appearing to be clinal (gradual) in geographic distribution: southern nests (bottomland hardwoods, Pearl River floodplain, Louisiana), compared to more northern, tended to be higher off the ground, farther from the tree trunk, better concealed within dense vegetation including vine tangles, smaller in size, thinner walled, and less likely to contain nest lining material (TWS, K. Williams, P. P. Marra, R. Norris, and S. Hannon, unpublished data). This latitudinal variation suggests a complex environmental gradient of ecological conditions affecting nesting behavior including potentially climate and predators, but the possible genetic basis of any such variation and selective pressures remain to be determined (see Priorities for Future Research).


Construction Process

Female alone builds nest (Sturm 1945, Bent 1953b, Ficken 1963a, TWS), taking 2.5–7 or more days (Sturm 1945, Bent 1953b, TWS). A female in Alberta took 5 d from start of building to laying of first egg (M.-A. Villard, personal communication). Sturm 1945 estimated that 1 female made 650–700 trips to build a single nest over a period of 2.5–3 d. This female made > 19 trips/h, working almost continuously for 14.5 h on second day of construction. Females obtain nest material from shrubs and trees, but also frequently from ground (Sturm 1945, Bent 1953b, TWS). A favorite nest material at Hubbard Brook, New Hampshire, is the bark of yellow birch, which females, while hovering, often tear from bole or large branches. Female spends considerable time shaping nest, by sitting down in cup, particularly as cup becomes well formed (TWS).

Structure and Composition Matter

Nest is a tightly-formed open cup, fitted to branches where located, constructed of variety of natural small fibers (birch and other thin bark strips, grasses, various plant downs and fibers such as milkweed seed hairs, animal hair, feathers, rootlets, mycorrhizae, leaves, lichens, twigs, mosses, pine needles, and paper of wasp nests (Baker 1944a, Bent 1953b, Peck and James 1987, TWS). Linings often include same kinds of materials, including feathers and mammal hair. Whole nest is generally “glued” together with spider silk. Outside is often covered with layer of bark, lichens, or other material that either camouflages nest against surrounding plant matrix (e.g., birch bark when constructed in birch trees; R. E. Lemon, personal communication, TWS) or flags it conspicuously against background of different color (Griscom and Sprunt 1957). Nests in Louisiana bottomland hardwoods contain rhizomorphs of Marasmius spp. (horsehair fungus) and some contain little else (TWS, unpublished data); this material has high tensile strength, low propensity to absorb water (Freymann 2008), and antibiotic properties, all of which may favor selection of these filaments by nesting birds including redstarts, particularly at low latitudes (Aubrecht et al. 2013).


Average dimensions of northern nests: outside diameter, 6.7–7.0 cm; inside (cup) diameter, 4.4–4.5 cm; outside depth, 6.3–7.6 cm; inside (cup) depth, 3.2–3.8 cm (Baker 1944a, Peck and James 1987, Sallabanks 1993e). Dimensions of Louisiana nests are smaller: mean outside diameter, 5.2 cm (range 4.67–5.51); mean inside (cup) depth, 3.5 cm (range 3.0–3.98).


Occasionally built under overhanging leaves, either for protection from weather or concealment from predators. Some nests are exposed to direct rainfall and full sunlight, at least during some times of day.

Maintenance Or Reuse Of Nests

Seven reported instances of nesting in open cup nest built by another species, including Red-eyed Vireo (Vireo olivaceus), and Yellow Warbler, suggest that this is not an infrequent behavior (Yezerinac 1993). Redstarts occasionally use other species’ nests when costs are small—e.g., opportunity to use a familiar nest type in familiar habitat—and advantages are great, such as potential to save considerable energy and time renesting because of nest failure late in the short temperate-zone breeding season (Yezerinac 1993).

When renesting, often reuses material from earlier nest attempt (Sturm 1945, TWS), or sometimes from inactive nest of another bird species (TWS). These observations reinforce idea that ability to locate nesting material and efficiency of nest construction are at a premium, particularly late in the short nesting season (Yezerinac 1993).


Shape, Size, And Mass

Ovate to occasionally short ovate; 16.2 × 12.3 mm length and breadth, respectively (n = 50 eggs; Bent 1953b). At Hubbard Brook, New Hampshire, mean egg dimensions: length 16.07 mm ± 0.12 SD; breadth 12.58 mm ± 0.09 SD; mass 1.20 g ± 0.02 SD (n = 38 eggs, 10 clutches; TWS). Eggs were weighed between day 4 and day 10 (where day 0 = clutch completion date); mass tended to decline (but not statistically significantly) with egg measurement date (TWS). Average egg mass is 13.8% of female breeding mass. Mean egg mass of 4-egg clutch in Ontario reported as 5.37 g + 0.34 SD (n = 10); and females estimated to produce 1.07 g yolk and 0.62 g yolk lipids in first clutches (Langin et al. 2007).

Based on stable-isotope analyses, female American Redstarts are reported to be “income breeders”, obtaining the nutrients necessary for producing egg contents (proteins and lipids) primarily locally from the diet at the time of egg laying (Langin et al. 2007).


Background slightly glossy white to creamy, speckled or blotched with usually distinct wreath—toward blunt end—of variegated brownish or reddish underlain by gray brown (Bent 1953b, TWS). Size and color vary; some eggs are nearly whitish, others are so speckled as to nearly conceal ground color (Bent 1953b).

Eggshell Thickness

Average thickness 0.071 mm ± 0.0073 SE, on basis of 8 eggs (from 8 clutches) at Hubbard Brook, New Hampshire, and Adirondack Mountains, New York (Keefe 1996).

Clutch Size

Mean clutch size was 3.82 eggs at Hubbard Brook, New Hampshire (n = 359 nests; TWS), 3.56 eggs in Ontario (n = 172 nests; Peck and James 1987), and 4.37 eggs in Alberta (n = 172 eggs; M.-A. Villard and S. Hannon, unpublished data). Throughout geographic range, modal clutch size is 4 eggs (range 1–5; Baker 1944a, Sturm 1945, Bent 1953b, Peck and James 1987, TWS). Small clutches (1–2 eggs) are unusual and tend to occur toward end of breeding season (TWS). Five-egg clutches are not rare, but tend to occur early in season (29 May–11 June at Hubbard Brook), which may help explain why some observers (e.g., Baker 1944a, Bent 1953b) have not reported 5-egg clutches. In Ontario study, 5-egg clutches accounted for 5.2% of total, 4-egg clutches (64.5%), 3-egg clutches (16.3%), 2-egg clutches (9.3%), and 1-egg clutches (4.7%) (n = 172 nests; Peck and James 1987). Similarly, percentages of 5-egg, 4-egg, 3-egg, 2-egg, and 1-egg clutches at Hubbard Brook were 5.6%, 72.4%, 20.3%, 1.4%, and 0.3%, respectively (n = 359 nests; TWS). In Alberta, by contrast, 5-egg clutches were relatively frequent (43%), 4-egg clutches (51%), and 3-egg clutches (6%) (n = 172 nests; M.-A. Villard and S. Hannon, unpublished data), consistent with general latitudinal increase in avian clutch sizes. Latitudinal change in clutch size reinforced by data from nests in southernmost breeding sites, Pearl River floodplain in Louisiana, where average clutch size was 3.61 eggs (based on 14 four-egg clutches and 9 three-egg clutches; TWS, unpublished data). Thus, redstart clutch size differs by almost 1 egg on average from Alberta (4.37 average) to Louisiana (see Nest Characteristics for details on latitudinal variation in nest and nest microhabitat).

At Hubbard Brook, clutch size decreases significantly over course of season (TWS), accounting for observed clutch size decreases of individual birds that replace lost clutches or broods (Baker 1944a, Bent 1953b).

Corresponding with declining clutch size over course of season, number of young fledged also declines linearly from almost 3 fledged offspring from initial nests to about 1 fledged young 25 days later (McKellar et al. 2013a; see also Demography and Populations: Measures of Breeding Activity: Annual and Lifetime Reproductive Success).

At Hubbard Brook, average clutch size differs significantly by age of male: 3.86 eggs for females mated to older males (n = 287 nests) versus 3.63 eggs for females mated to yearlings (n = 72 nests; effect of female age per se on clutch size is not known). The smaller average clutch associated with yearling males at Hubbard Brook results from later clutch completion dates, since age-specific clutch sizes were indistinguishable when examined by clutch completion date. Clutch size also differs by age in New Brunswick: Mean clutch sizes 2.9 eggs (n = 106 nests) and 2.1 eggs (n = 60 nests) for older male versus yearling male nests, respectively (Lemon et al. 1992).


One egg laid/d, early in morning soon after 05:00 (n = 3 eggs, 1 clutch; Sturm 1945, TWS). Female forages actively, often high in trees, during this period, and rarely visits nest site until incubation begins (TWS).


Onset Of Broodiness And Incubation In Relation To Laying

Female often begins sitting on the nest for longer and longer time periods on the day that penultimate egg is laid (TWS), and almost invariably sits regularly on eggs on day that last egg is laid.

Incubation Patches

Single medial abdominal patch in female only.

Incubation Period

Modal duration 11 d (range 10–13; Peck and James 1987, TWS) or 12 d (Bent 1953b, Griscom and Sprunt 1957).

Parental Behavior

Female alone incubates, spending more time incubating in colder weather (Bent 1953b). During incubation male occasionally feeds female; males provided 0.24 feeds/hr under conditions of latitude 41.65 and ambient daytime temperature of 21.9º C (Bent 1953b, Sturm 1945, Matysioková et al. 2011), most frequently at colder temperatures (TWS), which is probably what allows female to incubate for longer periods under such conditions, although further study is needed. Female nest attentiveness is strongly positively correlated to incubation feeding rate in passerine birds, consistent with observation that female redstarts are rarely absent from eggs for > 2–10 min, and spend about 85.3% of daytime hours incubating (Matysioková et al. 2011, Bent 1953b). Incubation feeding tends to decline with daily nest predation rate in North American bird species, but incubation feeding rate in redstart is relatively low considering its nest predation rate (from data in Matysioková et al. 2011). These behaviors likely vary with latitude and other relevant conditions (temperature, predator pressure) considering latitudinal variability in nesting behavior in redstarts (see Site Characteristics).

Arrival timing on breeding territories influences incubation behavior. For example, earlier arriving females begin to lay clutches relatively early, producing heavier nestlings than later layers (Smith and Moore 2005a). Females that arrive to breed with more body fat have better reproductive performance, indicated by larger clutch size, egg volume, and nestling mass (Smith and Moore 2003).

Hardiness Of Eggs Against Temperature Stress

No information.


Eggs typically hatch over about 24-h period, consistent with female's behavior of sometimes beginning to incubate on day that she lays penultimate egg (TWS).

Preliminary Events And Vocalizations

Not recorded.

Shell-Breaking And Emergence

Not recorded.

Parental Assistance And Disposal Of Eggshells

Egg-shells are removed from the nest site; a male removed shells at 1 nest even before feeding nestlings (Bent 1953b).

Young Birds

Condition At Hatching

Altricial and naked at hatching, except for downy tufts of feathers on head, neck, and dorsum; eyes are closed (Bent 1953b).

Growth And Development

Eyes open to narrow slits at 3 d of age, at same time wing-feather papillae appear (Bent 1953b). Flight-feathers break through sheathes at day 6, and Juvenile Plumage is worn by day 8. Chicks can jump from nest in response to disturbance by day 7 (TWS), but ordinarily remain until day 9. In Alberta, the nestling period typically extends to a 10th day (Hannon et al. 2009). Nestling body mass measurements include 5.0 g (day 4; n = 32 chicks at 8 nests), 7.5 g (day 7; n = 23 chicks at 6 nests); chicks not measured past day 7 to avoid risk of premature fledging (TWS).

Male retains female-like plumage as a yearling, until time of molting into Definitive Basic Plumage (orange and black), just after first potential reproductive season (see Appearance). This phenomenon, often termed “delayed plumage maturation” (Procter-Gray and Holmes 1981, Rohwer et al. 1983), can be considered one form of heterochrony (different development rates), in which male sexual maturation precedes plumage maturation (Lawton and Lawton 1986). Although a variety of hypotheses have been proposed to explain delayed plumage maturation and heterochrony, only a few have not been tested in American Redstart (see Other: Life-history Traits: Delayed Plumage Maturation and Sexual Selection).

Parental Care


Powerful tendency to brood by female, illustrated by her tendency to brood empty nest when chicks are experimentally removed (Bent 1953b). Brooding occupies up to 80% or more of daylight time soon after chicks hatch, especially in cold weather; declines toward end of nestling period. Reduced brooding with chick age probably results from increased ability of chicks to regulate body temperature independently, but this has not been studied in this species. Female redstarts extend their wings to protect young from sun (by providing shade) and from rain (Bent 1953b).


Both sexes feed chicks on nest, each parent typically making 50% of food-provisioning trips. Yearling male contributes as much as older male to nestling-provisioning (Omland and Sherry 1994, Omland and Sherry 1995). Mean feeding rates of yearling and older males was 8.2 trips/hr ± 4.6 SE and 6.8 trips/hr ± 2.2 SE, respectively; mean number of feeding trips made by the mates of yearling and older males was 6.6 trips/hr ± 2.8 SE and 6.4 trips/hr ± 2.6 SE, respectively (Omland and Sherry 1994). Mean mass of insect food delivered per hour to chicks (days 4–9 after hatching) estimated to be 56 mg ± 20 SE and 65 mg ± 37 SE for yearling and older males, respectively; and 30 mg ± 12 SE and 46 mg ± 27 SE for mate of yearling and older males, respectively (Omland and Sherry 1994). Polygynous male spends less effort than indicated by above averages when provisioning offspring at secondary, compared with primary, nest (Secunda and Sherry 1991, TWS), and widowed birds increase feeding rate (TWS). Both widowed male and female will feed brood alone (Bent 1953b, TWS).

Of prey types identified in prey loads brought to nests, moths (both caterpillar larvae and adult bodies with wings generally knocked off) and flies (especially crane flies, Tipulidae) dominated, but some wasps, beetles, and spiders are included (Omland and Sherry 1994). However, these data come from visual identifications, at a distance from nest, so they underestimate importance of small prey. Most prey loads taken to nestlings contain many small and sometimes a few large prey (sometimes dozens of items concealing beak; TWS), but nature of entire prey loads has not been quantitatively studied.

Nest Sanitation

Both sexes eat fecal sacs, especially in first 2 days of nestling period, then carry sacs away from nest (Baker 1944a, Bent 1953b), at least up until last day or so of nestling period, at which time fecal material tends to accumulate on and beneath nest rim (TWS). Since chicks 7–9 d of age can jump explosively from nest if predator attacks (TWS), need to remove fecal material from vicinity of nest may wane in final days before fledging. Parents remove fecal sacs many times per hour at active nests, especially later in nestling period, when chicks are large and growing rapidly. Parents often hover behind chick (e.g., sitting near edge or on rim of nest) to pick up sac as latter presents cloacal region in direction of adult (TWS).

Carrying Of Young

Not recorded.

Cooperative Breeding

Not described.

Brood Parasitism

Identity Of Parasitic Species

Only known brood parasite is Brown-headed Cowbird (Molothrus ater).

Frequency Of Occurrence, Seasonal Or Geographic Variation

Rates of brood parasitism estimated in several studies (Sturm 1945, Bent 1953b, Ficken 1961, Peck and James 1987, Sallabanks 1993e, Cyr and Darveau 1996, Sodhi et al. 1999, Falk et al. 2011): 68% (n = 34 nests), 74% (sample size not given), and 6% (n = 18 nests) in 3 New York studies; 32% in Ohio (n = 22 nests); 0% in Pymatuning Swamp in Pennsylvania; 17% in Driftless Area Ecoregion of Wisconsin, Minnesota, and Iowa (n = 267 nests); 20% in Ontario (n = 285 nests); 42% in Ontario (n = 39 nests); 15.8% (n = 145 nests) in Quebec, 64% in British Columbia (n = 11 nests), 18% (n = 22 nests) in central Alberta. In Illinois, 7% of 27 nests were brood-parasitized before 1900, 37% of 41 nests brood-parasitized after 1900 (cited by Friedmann and Kiff 1985). In Hubbard Brook, New Hampshire, cowbird parasitism of American Redstart nests never documented, even though a few cowbirds are found in the more open, human-inhabited valleys within about 10 km of study sites (TWS, RTH). Thus, redstarts are susceptible to brood parasitism wherever they come in contact with enough cowbirds, but cowbirds are too infrequent or far from redstart-preferred forested habitat to be a problem at both Hubbard Brook (TWS, RTH) and New Brunswick (R. E. Lemon, personal communication) study sites. Risk of nest parasitism may depend upon the proportion of surrounding habitat that is rural grassland (that includes cattle) or row crops, and hence also includes cowbirds (Hannon et al. 2009, Falk et al. 2011).

Timing Of Laying In Relation To Host's Laying

No information.

Response To Parasitic Mother, Eggs, Or Nestlings

Responds aggressively to cowbirds (Ficken 1961). Female redstart responds to female cowbird with “sharp hisses, a rapid snapping of the bill and much spreading of the tail” (Hickey 1940: 256). Sturm 1945 described a female redstart that used a Crouch Display in response to the call of a female cowbird, an instance of a female redstart that left her nest site for 20 min while a cowbird was being attacked by male redstart, and 2 instances in which a male redstart snapped its bill and flew aggressively toward a female cowbird (with tail spread). Ficken 1961 also recorded aggressive Head-forward Displays when a redstart approached a Brown-headed Cowbird within the redstart’s territory, accompanied by Snarls (see Sounds and Vocal Behavior: Vocalizations) and bill-snapping, followed by physical attacks on cowbird visiting the nest site. May abandon nest containing cowbird eggs, or build part of nest over cowbird eggs (Sturm 1945, Bent 1953b). Redstart populations that have a history of contact with cowbirds respond more aggressively to cowbird models (i.e., more close passes to cowbird model, tail-fanning, and contact with model) than populations that have had limited contact (Hobson and Villard 1998).

Effects Of Parasitism On Host

No information.

Success Of Parasite With This Host

Cowbirds parasitize American Redstarts successfully, on the basis of acceptance of cowbird eggs at some nests and observations of adult redstarts feeding cowbird fledglings (Bent 1953b, Ficken 1961; but see Klein and Rosenberg 1986). First confirmed breeding by redstart pair in California fledged a cowbird in 1972 (Small 1994). Parasitized redstart nests are abandoned about 7% of the time in the Driftless Area Ecoregion (Powell and Knutson 2006).

Fledgling Stage

Departure From Nest

Young generally leave nest over period of ≤ 1 h, although they frequently make excursions out along nearby branch for up to several hours before permanently departing nest site (TWS). Fledglings typically fly weakly at time of fledging; usually flutter to ground or near the ground, where they are vulnerable to predators for about a day before they can fly well enough to move up into canopy and follow adult.

Period From Hatching To Departure

Modal length of nestling period 9 d, although young can be easily disturbed into fledging at 7 or 8 d (Sturm 1945, TWS). Under unusual circumstances, such as death of 1 adult, nestlings may not fledge until 10–13 d (TWS).

Condition Of Development At Departure

Fledglings typically have substantial subcutaneous fat at the time of fledging and weigh about as much as adults. Wings and tail are about half grown at the time of fledging (TWS).

Association With Parents Or Other Young

Parents usually divide their brood after chicks have left the nest; thus, each parent feeds only particular fledglings (Boxall 1983, TWS). Parent generally remains with its part of brood for days to weeks; males appear more likely than females to remain in vicinity of the nest, on basis of observations that banded males (but not females) can often be located near the nest site for ≥ 1 mo after the fledge date (TWS). In 2 instances, a polygynous male “moved” his brood within few days of fledge date close to his secondary nest (by unknown mechanism; TWS).

Ability To Get Around, Feed, And Care For Self

Attending adults provide most food during the first week after fledging, and continue to feed chicks for up to 3 wk (TWS), although this has not been studied in detail. Parents probably force fledglings to become independent, as suggested by observation of older male attacking a begging fledgling that had left the nest 3–4 wk earlier (TWS).

Recommended Citation

Sherry, Thomas W., Richard T. Holmes, Peter Pyle and Michael A. Patten. 2016. American Redstart (Setophaga ruticilla), version 3.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.