A special colored patch or "speculum" on their wings flashes in the sunlight with a metallic sheen. Bird books describe how the males "repeatedly flash light" off these patches, to dazzle the females and win their hearts.
翅膀上稱為「翼鏡」的特有色塊，隨著陽光絢爛，不時反射金屬光芒，鳥類書籍上說它「常利用翼鏡反光」，閃得母鴨眼花撩亂，投懷送抱。