What distinct feature marks the more subdued female Wood Duck?

Answer

A noticeable white patch encircling her eye

While the male Wood Duck is famous for its multitude of colors, the female possesses a signature mark that aids in identification: a noticeable white patch surrounding her eye. Although the female is generally grayish-brown, this white eye-ring, along with a white throat area, helps distinguish her profile. She also exhibits flashes of iridescent blue-green on her wings, but the eye-ring is the key distinguishing facial characteristic.

What distinct feature marks the more subdued female Wood Duck?
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