Pato serrucho ’93

Philip Benstead

The Brazilian Merganser (Mergus octosetaceus) is one of the planet's rarest species of wildfowl, with an estimated population of fewer than 250 individuals. Three conservation biologists from the UK and three South American counterparts surveyed 450 km of whitewater rivers and streams using an inflatable boat. Despite exhaustive searches, only one individual was located in an area close to the species historical strongholds. Former core areas (and incidentally those with the most protection) seem to have been adversely affected by the completion of the Urugua-i dam in 1989, which flooded an estimated 80 km of the river Urugua-i. Habitat remnants upstream of the dam may also be subject to a higher density of fish-eating birds such as Neotropic Cormorant (Phalacrocorax olivaceus), which breeds in large numbers in the dam basin. Some travel upriver to feed in the Urugua-i and Uruzu rivers, and may therefore compete with Brazilian Merganser. Rivers not draining into the dam, including the Piray-mini (site of sole Merganser record), exhibited a much lower density of cormorants. Additional threats include deforestation and the resulting increased turbidity in rivers used by the Brazilian Merganser.

The survey results highlight the importance of further surveys of key rivers in the region and the extension of the protected areas framework in Misiones Province. "Otherwise we merely documented the further decline of the Brazilian Merganser in Argentina". Awareness-raising of conservation issues in developing countries was greater among the British members than among the Argentines, who are acutely aware of environmental problems in their own country. Argentina has a good conservation network. Expedition findings are being published as widely as possible and P. Benstead is appealing to the Argentine counterparts for ideas for a follow-up proposal (MKP questionnaire).

Project update: 13/2/98 The Brazilian Merganser is critically endangered by the perturbation and pollution (largely due to deforestation) of the shallow, fast-flowing rivers that are this duck’s habitat in south-central Brazil, eastern Paraguay and northern Argentina (Collar et al. 1994). The team did not fulfill its engagement to the National Parks Administration (APN) to study an area of Iguazú National Park (G. Gil in litt. 1998). One of the Iguazú National Park wardens involved in the project now works in the Perito Moreno National Park (J. Calo in litt. 1998).