Distinguishing Characteristics

Small oscine, 11.5–13.0 cm long, 12–18 g mass. Sexually dimorphic in plumage color in breeding season. Adult males all blue, head sometimes purplish blue. First-year males variable in plumage color, either blue or mixed blue and brown and white, some with buff wing bars. Females unstreaked or indistinctly streaked on breast, light brown with buff wing bars. Juveniles streaked and with buff wing bars. Bill short, conical. Rectrices medium length, truncate. Wing formula: P 7 ≥ 8 > 9 > 6 > 5, same as Lazuli Bunting (P. amoena).

Males differ from Lazuli Bunting in darker blue plumage, in underparts blue (breast orange and belly white in Lazuli Buntings), and in lack of wing bars (white in Lazuli Bunting), although some first-year male Indigo Buntings have some brown or white in plumage.

Females and Basic-plumaged males sometimes very similar to other brown-plumaged buntings. Plumage mouse brown above, nearly unstreaked, below buffy with whiteish throat and belly, breast finely streaked dark, often bluish on shoulder, rump and tail. Female and Basic I male Lazuli Bunting have more uniform pinkish-buff breast and throat (Indigo has whiter throat, contrasting with dull brown breast area which is often mottled or vaguely streaked) and more prominent wing bars. Indigo x Lazuli hybrids occur, and female-plumaged hybrids probably not all distinguishable. Female and first-year male Varied Bunting (P. versicolor) are more uniformly brown, lacking wing bars even in fresh plumage, and have a more curved culmen, giving a more stubby-billed look; different wing formula (P9 < P5). Juvenal of all three species extremely similar.