The black head and blue bill of the male is typical of the stiff tail group to which he is related, although he doesn't have an enlarged base of beak or even the stiff tail that gives the group its name. Black-headed Ducks are native to South America.
Females are "cuckoos", laying their eggs in nests of Rosybill Pochards and other ducks and coots; however their hatchlings don't destroy the hosts' offspring but hatch earlier and leave after a day to live independently.
The foreground duck would appear to be the female black-headed duck, a "probable" identification by duck expert
Joern Lehmhus of Germany. She was photographed the same day and in the same area as the male above, but in a
different location. The "background" duck is suspected to be a ruddy duck, another stiff-tail species.