a1 IWRB Threatened Waterfowl Research Group, The Wildfowl and Wetlands Trust, Slimbridge, Glos., GL2 7BT, U.K.
a2 Yew Tree House, Corscombe, Dorset, DT2 oNX, U.K.
The former and current status of the White-headed Duck Oxyura leucocephala is reviewed on the basis of recent census data and a literature search. The current world wintering population is estimated at 19,000 birds, with the likelihood that additional birds occur in unsurveyed wetlands in Asia. The population wintering in Pakistan appears to be declining, but there is no good evidence of current decline elsewhere in the range. The population resident in Spain is increasing. The greatest threat to the species is considered to be the spread of the introduced North American Ruddy Duck O. jamaicensis from the U.K. to the continent. Hybrids between the two species are fertile and have already been seen in Spain.