Northern Prairie Wildlife Research Center
| Wing Character | Male | Female | ||
| Adult | Immature | Immature | Adult | |
| Primaries | Outermost primary similar to and as long as or longer than the adjacent primary | |||
| Outer webs black | Outer webs dark blackish brown | |||
| Tertials | Shiny black and bluntly pointed; approximately 20 mm. longer than most secondaries | Dark brown and pointed; may be faded at their tips | Very dark blackish brown; tips bluntly pointed; usually less than 20 mm. longer than most secondaries | |
| Tertial coverts | Shiny black | Dark brown; noticeably narrower than those of adults; often faded at their tips | Very dark blackish brown; smoothly rounded tips | |
| Greater, middle, and lesser coverts | Entirely black; appear smooth | Dark brown; most greater coverts are faded at their tips; they often appear rough | Very dark blackish brown; some are slightly faded at their tips; all appear smooth | |