Breeding biology of the torrent duck (Merganetta armata armata) in Northwest Patagonia, Argentina
The torrent duck inhabits the rivers of the high Andes, specializing in fast-flowing waters from Venezuela to Tierra del Fuego. In Argentina, the species has been classified as endangered. Because of their high mobility, low density and the challenging terrain, they are difficult to study; however, there is evidence of population declines and loss of successful breeding sites, due to hydroelectric developments, introduced trout and erosion of riverside habitat. This study was designed to provide the first detailed description of the foraging behavior, breeding biology and habitat use of the species.
Researchers investigated the diet, prey selection and energy profile of key prey items of the torrent duck, sampling aquatic invertebrates from four regions and comparing prey availability with prey samples extracted from duck droppings. Results indicated that the ducks forage selectively relative to prey available in the environment, although they did not appear to select prey species with higher energy content. Black fly, mayfly, caddisfly and Gripopterygids larvae made up 80% of torrent duck diet at most study sites. However, where these species were rare or absent, ducks consumed other prey, suggesting versatile feeding behavior that would allow the species to adjust to changes in the river benthos without disappearing in a given environment.
While there were too few nest sites for extensive analyses, this study did provide the first comprehensive description of the timing and behaviors associated with the breeding cycle for torrent ducks – information that has not been available to date. The timing of courtship, nest-building, egg-laying, hatching and fledging were documented, as were the behaviors and roles of males and females during the breeding cycle. Unfortunately, for the five years during which these data were collected, the number of actively used nest sites declined from 35% to just 6% of suitable areas. The researchers suggest various potential causes that need to be explored, including human disturbance, alteration of hydrology regimes by dams, food competition from introduced salmonids and predation by introduced American mink.
The team has conducted outreach on the torrent duck at various local festivals and has been working on a documentary that is currently available in Spanish at http://vimeo.com/12150519. ($4,850)