(North American) Ruddy Duck Oxyura jamaicensis

Ruddy Duck
Ruddy Duck
The Ruddy Duck is one of the "stiff tail" family of ducks and is native to North America.
Ruddy Duck
Ruddy Duck
Ruddy drake: introduced from North America, the Ruddy Duck has colonised parts of the UK and Europe, interbreeding with the European White-headed Duck
Ruddy Duck female Female Ruddy Duck in a flap (with Tufted drake)
Ruddy Duck female Female Ruddy Duck
Ruddy Duck pairs

The black-headed duck below lives in Regent's Park, London. Like the North American Ruddy Duck and the Spanish White-headed Duck, he is one of the "stiff tail" family of ducks. He has a fully black head with no white on the face and a turquoise blue bill.
Similar to the small Australian Blue-billed Duck (Oxyura australis) and almost identical to the Andean Ruddy Duck (Oxyura jamaicensis ferruginea), he is actually an

Argentinian Ruddy Duck (Oxyura vittata) also called an Argentine Blue-bill.

Argentinian Ruddy Duck The lady with him looks like a North American Ruddy Duck but could be the South American female (above right); she is being pursued by both breeds (see below).
The female Argentine Ruddy Duck is similar to the female (north American) Ruddy Duck, though this one has less white and more brown on the cheek.
Argentinian Ruddy Duck
Argentinian Ruddy Duck
Giving her the full benefit of his powerful broad shoulders, thick neck and upright tail as he does a little dance on the spot for her.
However a North American Ruddy male has been hovering for a long time and sees his chance to muscle in when the female swims away from the Argentinian male.
As he dashes in at speed she swims and then flies as fast as she can back to her South American boyfriend.