Which Anseriformes subfamily includes stiff-tailed ducks such as the ruddy duck?

Stiff-tailed ducks, such as the ruddy duck, belong to the subfamily Oxyurinae within the order Anseriformes.1

While some classification systems place the tribe Oxyurini within the subfamily Anatinae, other taxonomic frameworks recognize Oxyurinae as a distinct subfamily comprising eight species of stiff-tailed ducks across three genera. These birds are primarily found in the Southern Hemisphere and are characterized by their specialized, stiff tail feathers used for steering underwater, as well as their difficulty moving on land due to the position of their legs.213