The first known breeding record of Ruddy Duck Oxyura jamaicensis in the Netherlands dates from 1973, when a pair was found at Nieuwkoopse Plassen in Zuid-Holland. Since then the number increased to circa 20 breeding pairs, while the maximum number of wintering Ruddy Ducks was estimated at 100. The current 'hot spots' are Vogelplas Starrevaart at Leidschendam, Markiezaatsmeer in south-western Noord-Brabant and Oostvaardersplassen in Flevoland. The preferred breeding habitat consists of small, reed-fringed pools and lakes. The population may originate from the feral population in Central-England, present since the late 1940s and comprising circa 6000 Ruddy Ducks around 2000. The expansion and increase of the species is seen as a threat to the native and globally threatened White-headed Duck Oxyura leucocephala, since hybridization between both species was recorded in Spain. Therefore, in several European countries action has been taken to halt the spread of the Ruddy Duck.