The Ruddy Duck (Oxyura jamaicensis) originates from North America, the Caribbean Islands and South American countries of the Andes mountain range. In 1948 three pairs were introduced from the United States and added to the collection maintained by the Wildfowl and Wetlands Trust in Slimbridge in Britain. These individuals reproduced in captivity and later escaped, and some were even released intentionally, giving rise to a large wild population of Ruddy Ducks in Britain. This population continued to rise and reached more than 3500 individuals by 1992, already having established a presence in various neighbouring countries: Ireland, Iceland, France, Belgium, Germany, Italy, Sweden, Spain and Morocco.

In Spain the first sighting of the Ruddy Duck was made in 1983. It came into in contact with the indigenous species (Oxyura leucocephala) and gave rise to hybrid individuals. This artificial break in the geographical barrier that existed between the species resulted in hybridisation and the production of individuals distinct from the two original species.
Hybrids have been spotted in Spain since 1990. A number of meetings by experts in the conservation of the White-headed Duck have been held in Spain and, given the grave state of affairs, it was decided that the only possible solution was the selective elimination of the Ruddy Duck and hybrid individuals. These measures have been in force since 1990. Between 1991 and 2001 it has been estimated that about a hundred Ruddy Ducks arrived in Spain. Of the resulting population some 98 pure bred Ruddy Ducks and 58 hybrids were eliminated during the same period. The current level of the problem is unclear but far from being resolved. In France some 107 ducks have also been eliminated. In contrast, about 2200 individuals have been counted in Britain. In Holland and Belgium there is no check on the species and in Germany a few individuals have been spotted.

The Ruddy Duck appears to have less strict ecological requirements than the White-headed Duck and adapts better than the indigenous species. Despite the measures taken, the polygamous behaviour of the foreign duck, its greater aggressiveness during mating and the low population number of the White-headed Duck could lead to the extinction of the indigenous species.

During the national and international meetings which have taken place in Arundel (Britain, 1993) and Cordoba (Spain, 1994), hybridisation has been established to be without doubt the most serious conservation problem which faces the Spanish White-headed Duck population. In the same vein, BirdLife’s European Action Plan considers this danger “critical”.

More information (in Spanish) in “La Malvasía en el Mediterráneo occidental” (The White-headed Duck in the Western Mediterranean) [PDF].
Since January 2000 a team has been in charge of the detection and elimination of individual Ruddy Ducks and its hybrids in the nature park ‘El Hondo’. This team has been very successful with 19 Ruddy Ducks exterminated since its inception. The team is able to eliminate individuals just a few hours after being spotted and its efforts have been nationally recognised.