Appearance

Male buntings in breeding plumage (below, "Alternate") in spring and summer, in non-breeding "Basic" plumage in autumn and winter. Female plumage molts twice a year at time of male plumage, the plumages do not differ with the seasons. Post-juvenile ("Pre-basic") molt begins shortly after fledging, some young birds have two such molts before autumn migration. Birds of the year and older adults (including first-year birds) begin postbreeding molt on breeding grounds and mainly complete it there; a few birds of the year complete the molt on their winter grounds. Birds molt into breeding plumage on wintering grounds, beginning in late Feb and Mar (Johnston and Downer 1968, Taber and Johnston 1968, Emlen 1969, Alvarez del Toro 1980, UMMZ).

Color terminology follows Kornerup and Wanscher (1967). First number refers to plate number (hue), letter to column of the color plate (intensity or saturation), second number to row (tone, degree of gray); hyphens indicate observed ranges. Color names in quotations follow this reference, in which Munsell values are available.

Males in Alternate (breeding) plumage are “greyish blue.” Yearlings in first spring and summer less purplish and less saturated than older males. Intensity and saturation overlap considerably between age groups, and males brighter in fresh plumage. Crown, also sides of head, sometimes throat, 20–21–C–D–7; back, 21–22–B–C–6; breast, 20–22–B–C–6; belly, 20–22–B–C–6. Flight feathers bluish gray, 21E2, outer edges grayish blue, 21D6. Females in alternate plumage “light brown,” crown and back 5D5 fading and wearing to “greyish brown” 5–D–3–4 by end of summer; breast and under tail coverts grayish orange or orange gray, 5–B–2–3, breast with faint “brownish grey” streaks 5C2 fading to 5B2 by end of summer; chin, belly, and under tail coverts paler, whitish; wing bars buff 5–A–B–3–4; flight feathers “brownish grey” 5E2 to “greyish blue” 21D6, sometimes washed with more bluish, with edges buff or “brownish orange” 5C4 to grayish blue.

Juvenal plumage, above, color as in adult female, “light brown” 5D5, or more buff rufous; below, paler, breast buff 5–A–B–3, often with distinct “brownish grey” streaking on breast; otherwise like adult females in fresh plumage.

Juvenal Plumage

Above, brownish, plumage color uniform (unstreaked or obscurely streaked), the throat and upper breast to belly streaked dark gray (streaks usually fine, occasionally conspicuous and broad), flanks buff, wings dark brown, two buff wing bars (pale tips on greater and middle secondary coverts). Body plumage soft and fluffy. Streaking on breast variable in both sexes, streaks present in some nestlings ready to fledge and short-tailed juveniles. Male occasionally have bluish cast to rump and edge tail feathers, females lack bluish (sex determined when birds returned next year, RBP). Differs from adult female plumage by wing bars buff (paler whitish by this season in adult), breast with buff wash (white in summer in adult), flanks buff (whitish in adult) and head and back plumage more rufous buff (more gray in this season in adult).

Juvenal plumage develops in two stages, the first set of feathers nearly fully grown at fledging, the second set of feathers begins to emerge at margins of existing feather tracts, completed at time of completion of juvenile flight feathers. In second stage, pinfeathers first appear lateral edge of sternal tracts and dorsal tract on day 11, malar, chin and medial and lateral edge of sternal tracts and dorsal regions and the marginal coverts on day 14, under wing marginal coverts and coverts of remiges on day 17, chin and sternal region and humeral tract on day 20, occipital region on day 23 and interscapular region on day 35; feathers in brush stage with feather sheath less than half length of feather appear on dorsal region days 20 to 35 (Yuri 2002). Wing and tail as in adult female, with or without blue on rump and tail.

Prebasic I (Postjuvenile) molt complete for body plumage except greater primary coverts, and sometimes flight feathers. Early broods may acquire unstreaked first Basic plumage by 20 Jul. This early molt occurs in young hatched and fledged in the first half of the season, and it adds an extra molt and plumage to the sequnce in Indigo Buntings. The young hatched early in the season have an extra "postjuvenal molt" (less appropriately "prebasic molt") compared with young hatched later in the season, in hand-raised birds (Yuri 2002). Some early-hatched buntings may molt directly into Basic I plumage shortly after fledging (Sutton 1935, but the specimens in question (UMMZ 74953, 74957) are streaked just as are some feathered nestlings and appear to be streaky-plumaged juveniles; they were accompanied by an adult pair (Sutton 1935). In summer, young are distinguished from adult females by yellowish gape and by plumage (adults in worn female plumage have ragged tail and wing, dark gape, narrow whitish wing bars). Molt of body plumage is usually completed before autumn migration but may continue on the wintering grounds. Molt of Juvenal flight feathers usually begins later in summer (Graber 1955; Fig 5). Some birds of the year molt the tail and outer primaries, or all the primaries and secondaries, on breeding grounds; others complete molt in autumn on the wintering grounds (Yuri 2002).

Basic I Plumage

Brownish, unstreaked above and below, two buff wing bars; greater primary coverts brown. Males typically brownish with gray base of feathers, often with trace of bluish on upper lesser secondary and marginal coverts of wing, the edge of the tail feathers and rump, and have a distinct malar stripe. Females lack bluish color and malar stripe. Male head, chin and breast sometimes "scaly blue" with a dark central and basal feather vane and a buff margin, and the rump nearly all blue in this plumage. Blue in plumage is typically bilaterally symmetrical. Females lack the bluish color and malar stripe (Johnston 1967). Some males of the year were said to have a "supplemental" plumage, molting on wintering grounds from a brownish Basic I plumage to a mixed blue and brown plumage after autumn migration (Rohwer 1986), but this mixed autumn plumage is in fact an extended mixed juvenile—Basic I plumage undergoing a molt that continues from the breeding grounds into autumn on the wintering grounds (Johnston and Downer 1968). Most birds on the wintering grounds in autumn are not growing feathers, and nearly all males of the year are brown in plumage, in contrast to the partly-blue older adult males. Timing and sequence of molt varies among birds as much as does the growth of juvenal plumage(s). Replacement of feathers is not restricted to first-year males, as some adult males and females replace feathers during autumn (AMNH, FMNH, MCZ, USNM). Nearly all yearling males that were reared from the nestling stage and kept in captivity were < 10% blue through Dec (RBP). Homology of molts and plumages in Passerina is problematic, depending whether the criterion of homology is the sequence of molts or the visual appearance of plumage (Thompson and Leu 1994, Groschupf and Thompson 1998, Yuri 2002).

As a test of different molts in relation to age and sex on the wintering grounds in the Florida Keys, s. Lousiana, Mexico, Central America and the West Indies, of the 519 museum specimen skins with data and date and locality, 185 were taken in autumn (Sep through Nov) and were examined for molt. The contour feathes of each bird were separated at the base with forceps, under a lighted magnifier. In a second examination, the contour feathers were separated with a flexible air hose when the air flow directed at the skin exposed the base of the feathers. The second technique revealed most of the body plumage, more than 1,000 contour feathers in each study skin. Birds were scored for the presence and number (0, 1-10, > 10) of growing body feathers, which were recognized by finding a feather sheath at the base of the feather vane. A few specimens that were marked on the label as questionable sex or that were apparently mis-sexed by plumage, were re-sexed by wing length (e.g., UF 4794, all brown in plumage with a 64-mm wing and with a label marked "male" was clearly a female). Adult males were aged by the presence of all blue greater primary coverts; males of the year were aged by the presence of all brown greater primary coverts, and females could not be consistently aged by plumage. In these autumn buntings, 24 adult males were not in molt and four were molting; in the males in their first year 28 were not in molt and seven were molting; and in females 53 were not in molt and 18 were molting. Neither adult males nor males of the year had a high proportion of blue in their plumage, except one male (YPM 21661) from Yucatán which had 60% blue plumage; its greater primary coverts were worn and brown, its blue contour feathers were much faded, and its growing feathers were all brown. The lack of differences in molt in relation to age and sex, and the lack of growing blue feathers during this period in first-year male buntings do not support the idea of a "supplemental" molt or plumage, or that first-year males have an advantage in feeding competition owing to a blue plumage, both ideas suggested by Rohwer (1986). The occurance of a few growing feathers in an otherwise brown plumage more likely indicates that some birds migrate south from their breeding grounds before they have completed the post-juvenal or post-breeding (or pre-basic) molt, and then complete the molt on their wintering grounds.

Individuals vary in extent to which the primaries, secondaries, and rectrices involve a replacement of Juvenile plumage; some retain all the flight feathers (except for the inner three secondaries, which are replaced), some replace all, and most replace several outer primaries, resulting in the outer primaries being darker, less worn, and edged blue in males (returns of male and female buntings banded as nestlings and of known age; RBP). Wing, tail described above.

Prealternate I Molt

Basic I plumage followed by molt of body plumage on wintering grounds, observed in wild birds recaptured through the winter in Florida and Jamaica (Johnston and Downer 1968). In first-year males, some brown feathers grow at this time; in more birds the growing feathers are blue, or blue with a buff tip. A few males arrive on northern breeding grounds in early May still growing blue feathers on the head (RBP).

Alternate I Plumage

Males: one or more (usually all) greater primary coverts and greater secondary coverts brown, other tracts variably bluish, sometimes entirely blue except for greater primary and secondary coverts. Usually blue areas more extensive than brown, feathers often with brownish or buff edges on upper parts, wing, breast, belly, or under tail coverts, including brownish-edged feathers blue or gray at base, often with buff (not white) wing bars, often whitish on belly and under tail coverts, and inner three secondaries worn and brown. Some males are bilaterally symmetrical, others asymmetrical in pattern of blue; asymmetry allows individual identification of many first-year males in spring. Most males in first breeding season are only partly blue with as much as 80% brownish and white in plumage. About half the first-year males in e. United States in spring and summer have at least some white feathes on belly (Kroodsma 1975, UMMZ). Males are remarkably variable in the extent of blue, perhaps due both to the extent of winter molt into breeding plumage and to the wear of the brown tips of the body plumage. Males hatched early in the previous year tend to be more bluish than males hatched later in their natal year. Hatching date through natal season explains about 30% of the variance in plumage color (proportion of blue in body plumage, in yearling returns of banded nestlings; RBP). Lores blackish. Outer primaries (often number 6-9) blue edged and inner primaries brown edged; occasionally all primaries brown edged and retained from Juvenal plumage, some males have all primaries blue edged.

Females, similar to Basic I plumage, occasionally with blue in shoulder. Wing bars become less conspicuous through the breeding season due to wear. Primaries uniformly "brownish grey" with paler edges in known first-year females by the breeding season (RBP).

Definitive Prebasic Molt

Complete molt of body and flight feathers in late summer. Molt begins with the brown cheeks on males as they sing in August; most birds cease singing before they are noticeably in mixed blue-and-brown plumage. Females with young in nest do not molt; plumage may become quite worn by Aug and occasional females have tail 10 mm shorter when worn in late summer than when fresh.

Definitive Basic Plumage

Males: similar to Basic I plumage, except that greater primary coverts are all bluish edged, variably bluish on other tracts, occasionally with blue areas of underparts "streaked or scaly blue" the blue more extensive than brown, often with brownish or buff marks on upper parts, wing, breast, belly, or under tail coverts, including brownish-edged feathers with blue base, often with whitish on belly and under tail coverts. Contour feathers often buffy brown on 2-3 mm of the edge and tip, and blue below the buff edge, the blue concealed by overlapping tips, and the body plumage becoming more blue through the wear of the tips. Primaries and secondaries edged bluish. Lores blackish. Female plumage is all brown or less often brown variously tinged with blue on greater primary coverts, shoulder, rectrices, rump or rarely on other tracts. Wing, tail as described above.

Definitive Prealternate Molt

Males and females molt body plumage on the wintering grounds beginning in Feb, more often in Mar, and completed in late Mar to Apr before leaving in migration (Johnston and Downer 1968, Wetmore et al. 1984, FMNH, MCZ, UMMZ).

Definitive Alternate Plumage

Males: blue with blackish lores, greater primary coverst and greater secondary coverts black with blue edges. Adults occasionally with brownish or buff marks on upper parts, wing, breast, or under tail coverts, or buff wing bars or whitish on belly, or a combination of such tracts. Primaries and secondaries typically dark and edged in blue. A few males in later years (second through eighth) partly brown, occasionally more brown than blue; resemble males in Alternate I plumage except for blue greater primary coverts (banding returns, RBP, UMMZ). Males that are partly brown in breeding plumage in one year often return in all-ble plumage in the next year, and some adult males blue in one year return with brown and white patches in the next year (RBP). Plumage color (n = 5) determined metrics with reflectance spectrophotometer, breast brighter than head and back (peak reflectance and total reflectance). breast plumage, peak reflectance 45-55% at 480-520 nm on back with second peak in ultraviolet c. 320-360 nm; 10% or lower reflectance above 600 nm . Head plumage, peak at 420-480 nm with secondary peak as on breast. Back plumage, peak at 520-550 nm with plateau or secondary peak at shorter wavelengths into ultraviolet; the back plumage above 550-580 nm higher reflectance than plumage of head or breast (RBP).

Females: all brown, similar to female Basic I plumage, usually but not always, tinged blue on greater primary coverts, shoulder, edge of rectrices and rump, occasionally other tracts. The pattern of blue in birds recaptured year to year is consistent within an individual and is independent of age, at least in birds two years and older (RBP). A few females are bluer than the brownest males (mainly first-year males) in breeding plumage. Females with buff wing bars in fresh plumage, become paler with wear, and wing bars become obscure, pale and narrow, through the breeding season. Wing, tail as described above. Female Indigo Buntings differ from female Lazuli Buntings in having more distinctly streaked breasts and no wing bars, and the throat feathers are white compared with the cinnamon throat of Lazuli Buntings.

Bill And Gape

Males (adults in breeding season): upper mandible blackish, especially on culmen, lower mandible including the mandibular rami blue-gray, the gonys blackish. First-year males have yellowish gape into May, then it becomes dark gray. Females: upper mandible brown to blackish, the lower mandible pinkish horn color, the gape in spring yellowish until nesting when it changes to horn color. Males and females, all ages, nonbreeding season: bill paler, whitish to brownish or blue-gray, gape yellowish; the gape first appearing yellowish during molt in late summer.

Iris

Dark chestnut brown in adults; olive brown in first weeks of life.

Legs And Feet

Dull blue-gray to blackish.

Linear

Taken from live breeding birds in southern Michigan, except tail length and toe length from Michigan study skins in UMMZ (RBP).

Bill length: Males: n = 1139, range = 9.00–11.83 mm, mean = 10.56 ± 0.43 SD. Females: n = 556, range = 9.6–12.4 mm, mean = 11.19 ± 0.41 SD. Increases slightly through the summer as the adults feed on soft-bodied insects and berries (Payne and Payne 1989).

Wing length (arc, flattened): Males: n = 1135, range 62.7–73.6 mm, mean 68.40 ± 1.49 SD mm. First-year males average 1 mm shorter than older males. Females: n = 558, range = 58.8–69.0 mm, mean = 64.28 ± 1.47 SD. Wing length decreases through the breeding season, especially in females; wear is less than 1 mm in 100 days (Payne and Payne 1989).

At Powdermill Nature Reserve, Rector, PA (sw. PA), spring and fall migrants (Mulvihill et al. 2004): Female (adult) 63.2 mm ± 1.32 SD (60.5-66.0; n = 981); female (immature) 62.7 ± 1.36 (60.5-66.0; n = 152). Male (adult) 66.7 ± 1.59 (63.0-70.0; n = 1,096); male (immature) 65.7 ± 1.42 (63.0-69.5; n = 217).

Tail Length Males: n = 10, range = 47.2–51.4 mm, mean = 49.40 ± 1.51 SD. Females: n = 10, range = 44.6–48.0 mm, mean = 46.30 ± 1.35 SD.

Tarsus length: Males: n = 1130, range = 16.0–18.3 mm, mean = 17.16 ± 0.54 SD. Females, n = 566, range = 15.0–18.0 mm, mean = 16.61 ± 0.59 SD.

Longest (number 3) Toe length Males: n = 10, range = 16.2–19.0 mm, mean = 17.80 ± 0.92 SD. Females: n = 10, range = 16.0–18.0 mm, mean = 17.47 ± 0.79 SD.

Mass

As above (s. Michigan), breeding season (RBP): Males: n = 1,111 , range = 12.5–17.5 g, mean = 14.97 ± 0.73 SD. Females: n = 398, range = 11.9–18.5 g, mean = 14.38 g ± 9.56 SD. Female mass varies with nesting status, mean = 14.63 g ± 0.76 SD before nesting (n = 12, no brood patch), 15.17 ± 1.27 nestbuilding (n = 11), 14.62 ± 1.01 (n = 19, vascular brood patch), 15.10 ± 0.78 incubating (n = 102, edematous brood patch), 14.02 ± 0.81 feeding nestlings (n = 254, wrinkled brood patch).

At Powdermill Nature Reserve, Rector, PA (sw. PA), spring and fall migrants (Mulvihill et al. 2004): A) low fat (Fat Score 0): female (adult) 13.7 g ± 0.86 SD (11.6-16.4; n = 237); female (immature) 13.5 g ± 0.77 SD (11.3-15.8; n = 568); male (adult) 14.7 g ± 0.84 SD (12.7-17.7; n = 317); male (immature) 14.2 g ± 0.82 SD (12.1-16.6; n = 678). B) high fat (Fat Score 3): female (adult) 16.5 g ± 1.18 SD (14.1-19.3; n = 72); female (immature) 16.4 g ± 1.37 SD (13.8-19.8; n = 54); male (adult) 17.4 g ± 1.29 SD (14.9-20.3); male (immature) 17.0 g ± 1.26 (13.9-19.8; n = 60).