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Throughout the world there is probably no more rigorous environment for waterfowl than that provided by the Andean streams in South America. Rushing down the mountains from an altitude of 18,000 feet or more, tumbling over precipices, the streams eventually merge and grow into such giants as the Orinoco, Amazon, and Rio de la Plata on the Atlantic slope, or empty direct into the Pacific on the west side. In the intermediate elevations, mainly between 5,000 and 10,000 feet, a remarkable duck, fittingly called the torrent duck (Merganetta armata) makes its home among the rapids and cataracts. This bird, which ranges from northwestern Venezuela to the sub-Antarctic climate of Tierra de Fuego, occurs in scattered populations throughout the Andean chain wherever its specialized habitat requirements are met. These requirements include cold, well aerated water rich in aquatic insect life, large boulders protruding from the stream to provide resting places and foraging areas, and adjacent cliffs with holes or crevices for use in nesting.
Since roads rarely penetrate the Andes in the areas where torrent ducks thrive, it is not surprising that few biologists have had the good fortune to observe this species in situ. In fact, so little has been learned about torrent ducks that there is considerable doubt as to the number of species that should be recognized, various authorities having suggested that one, three, five, or six different species might exist. With such basic questions in doubt, it is not surprising that uncertainty or even complete ignorance has existed as to the details of the torrent duck’s biology, its feeding, nesting, social, and sexual behavior, and its probable evolutionary relationships to other waterfowl.
In the hope of answering at least some of these questions, I had been eager for many years to study the torrent duck. As I had previously studied all of the other 42 living genera of ducks, geese, and swans, Merganetta represented my last major goal.