Indigo Bunting (Passerina cyanea) Science Article 3
Dwight pointed out (1900, p. 211 et seq.) long ago that the Indigo Bunting replacessome outer primaries at the postjuvenal molt. These replaced primaries (in the male) have blue outer vanes contrasting sharply with the blackish outer vanes of the juvenal primaries, except that primary 9 has a black outer vane in each plumage, that is, juvenal and first winter.
Charles H. Blake, Bird-Banding, 36(4): 270