The mallard or wild duck (Anas platyrhynchos) is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argentina, Chile, the Falkland Islands and South Africa. This duck belongs to the subfamily Anatinae of the waterfowl family Anatidae.
These ones have been seen in a little town in Catalonia.
The male birds (drakes) have a glossy green head and are grey on wings and belly, while the females have mainly brown-speckled plumage. Mallards live in wetlands, eat water plants and small animals, and are gregarious. This species is the ancestor of most breeds of domestic ducks
More info: Wikipedia