ABSTRACT The mainland population of the ruddy-headed goose (Chloephaga rubidiceps) breeds in southern Patagonia and winters in the south of Buenos Aires province (Argentina), with a recent estimated size at around 900 individuals. This population is considered "in danger of extinction", while the Malvinas (Falkland) Islands population is in well conservation status, with an estimated size of 40,000 birds. The aim of this work is to contribute with updated information about the ruddy-headed goose's population wintering in southern Buenos Aires province. The specific objectives were to better delimit its wintering area, to look for sites with large numbers, to study its habitat used, and to identify main threats to the species. Two intensive surveys were conducted during the austral winter of 1999. The results: (1) confirm the low abundance of the ruddy-headed goose supporting its critical conservation status, (2) corroborate its very restricted distribution, with more than 80 % of sightings concentrated in an area of 13,000 ha in southern Buenos Aires province, and (3) suggest that changes in the species' habitat use during the wintering season appear to be a response to changes in habitat availability, resulting from the growth of crops and pastures. The overlap between the species wintering distribution and the main wheat cropping areas of Argentina results in serious threats to this goose. Management actions are discussed to contribute to the conservation of this endangered species.