Feeding Habits of Torrent Ducks (Merganetta Armata Armata) in Nahuel Huapi National Park, Argentina

Abstract. The Torrent Duck (Merganetta armata) is a little-known species that feeds on benthic invertebrates in fast-flowing mountain rivers and streams from Venezuela to Tierra del Fuego. In Argentina the species is classified as Threatened but basic studies of its resource requirements are necessary for conservation. Prey selection by adult Torrent Ducks was investigated by comparing the proportion of prey species in duck faeces with the proportion available in the benthos. Faeces and benthos were sampled seasonally over one year, from four territories in the Manso River Basin, Nahuel Huapi National Park, northwestern Argentine Patagonia. Filter feeding Simuliidae larvae (Diptera, 41–76% number of total prey) were consumed in greater proportion than their abundance. In Arroyo Blanco, an oligotrophic stream, Simuliidae were absent and the most important prey were Gripopterygidae larvae (Plecoptera, 53%) and Blephariceridae larvae (Diptera, 23%). Simuliidae may be easy prey because, like other filter feed...