The Chiloé wigeon (Mareca sibilatrix), also known as the southern wigeon, is one of three extant species of wigeon in the genus Mareca of the dabbling duck subfamily. This bird is indigenous to the southern part of South America, including the Chiloé Archipelago.
This bird has an iridescent green-blue cap on its head, and a bluish gray bill with a black tip. The cheeks and forehead are white, the eyes are dark brown, and there is a white auricular patch. The neck and occipital part of the head are black. The breast is barred black and white and the plumage of the wings is gray and white. The flanks of males are rust colored, and light brown on females. The legs and feet are gray.
Sexual dimorphism is relatively subtle in this species of wigeon. Males are usually somewhat larger and heavier, and with somewhat brighter plumage and more strongly pronounced iridescence of the cap. Apart from these features, it can be difficult to distinguish the two sexes. Juveniles resemble adult birds, but the rust coloring on the flanks is diminished or absent.