The stripe on the most distal tertial is the most useful indicator of sex. On the wings of males, this stripe is black and sharply delineated from the basic feather color. On the wings of females, this stripe is black to brown, but grades into the basic feather color. The sex of approximately half of the immature birds can be identified by measurements. Wings 183 mm. or longer are from males and wings shorter than 175 mm. are from females, but sex cannot be determined from measurements between 176 mm. and 182 mm. A sample of wings from Adak Island, Alaska, green-winged teal (considered a different subspecies) averaged approximately 5 percent longer than wings collected in the lower 48 states. The number of iridescent secondaries differs between sexes. Wings having fewer than four secondaries with completely iridescent green outer webs are usually from females and wings with five or more such secondaries are usually from males. Sex cannot be determined in this manner from wings with four or four and a half iridescent secondaries.
Immature tertials are small, narrow, and rather delicate. The tips of these feathers are often badly frayed. Adult female-type tertials have cream colored edging. Adult male-type tertials are long, without edging, or with narrow edging. The presence of adult-type tertials is not by itself an indication of age. Many green-winged teal molt tertials during the hunting season. For some of these, it is possible to split incoming pin feathers to see whether the new feather is male or female in character. For wings with molted tertials, determination of sex is not possible.
Tertial coverts that are long and narrow, showing fine, light edging, and a frayed fringe are remnants of immature plumage and positively identify the wing as being immature. The tertial stripe may be used to separate the sexes. Adult female-type tertial coverts are broadly rounded with wide edging that is cream or brown. Adult male-type tertial coverts are a uniform gray, sometimes with a narrow buffy edging, and tapering to a blunt point. Adult-type tertial coverts are not a reliable indicator of age.
Middle coverts of adult males are smooth and without edging. Middle coverts of immatures are rough and may show gray-appearing wear at their edges. Immatures may also possess light edging which is more pronounced on females, but may also be present on males. Broad, rounded middle coverts with wide edging are found only on adult females. Traces of immature plumage usually remain most obvious immediately anterior to the tertial coverts.
| Wing Character | Male | Female | ||
| Adult | Immature | Immature | Adult | |
| Scapulars | Vermiculated or barred or both | Barred | ||
| Tertials | Uniform gray; tapering to a narrow rounded tip; unfrayed; rarely have narrow light edging; black longitudinal stripe sharply defined along inner edge; may be molting | Small; narrow; rather delicate tips are often badly frayed; usually buff edging | Buff edging including rounded tips; unfrayed; longitudinal stripe often poorly defined along inner edge; may be brown or black; stripe sometimes well defined; may be molting | |
| Longitudinal stripe usually black and well defined | Longitudinal stripe usually brown and poorly defined along inner edge | |||
| After molt: Similar to adult male | After molt: Similar to adult female | |||
| Greater tertial coverts | No edging; gray; may be either rounded or pointed; not frayed or faded | Narrow with fine light edging; often faded or frayed to wispy tips | Broadly rounded; usually with wide light edging; not frayed or faded | |
| After molt: Similar to adult male | After molt: Similar to adult female | |||
| Middle and lesser coverts | Broadly rounded; no edging; gray that matches tertial coverts | Gray with wear around edges; appear ragged; somewhat narrow and trapezoidal; late in year contrast to a variable degree with new (replaced) greater coverts | Broadly rounded; usually with wide light edging but sometimes no edging | |
| Primary coverts | No edging to a trace of light edging on inner web of outer four | Usually with considerable light edging on inner webs of outer four | No edging; or faint, light edging on inner webs of outer four | |