(African) White-backed Duck Thalassornis leuconotus
The White-backed Duck, also called the African White-backed Duck, is native to sub-Saharan Africa.
Pink-necked or Striped might be a more appropriate name since their white backs are rarely seen.
They have a call reminiscent of the Whistling Ducks and a tail like the Stiff-tail Ducks but are not closely related to any other species of duck.