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 feeders, they feed in exposed places. However, where these filtering species are rare or absent (as in Arroyo Blanco), ducks consume other prey. The results show that Torrent Ducks exhibit a versatile feeding behavior, indicating that the species can adjust to changes in the benthos without disappearing in a given environment.

[1]  J. Gee.  Specialist Aquatic Feeding Mechanisms , 2009 .

[2]  S. Canton,et al.  Guía para la determinación de los artrópodos bentónicos sudamericanos. H. R. Fernández , E. Domínguez , 2003 .

[3]  M. Robert,et al.  SUMMER FOOD HABITS OF HARLEQUIN DUCKS IN EASTERN NORTH AMERICA , 2001 .

[4]  D. Callaghan.  Conservation status of the Torrent Ducks Merganetta , 1997 .

[5]  A. Green.  Analyses of Globally Threatened Anatidae in Relation to Threats, Distribution, Migration Patterns, and Habitat Use , 1996 .

[6]  F. Rojas-Suárez.  Libro rojo de la fauna venezolana , 1995 .

[7]  K. Collier,et al.  Foraging ecology of blue ducks Hymenolaimus malacorhynchos on a New Zealand river: Implications for conservation , 1995 .

[8]  G. Host,et al.  Identification of predominant environmental factors structuring stream macroinvertebrate communities within a large agricultural catchment , 1993 .

[9]  Liliana Braga.  Fauna de agua dulce de la República Argentina , 1993 .

[10]  K. Collier.  Invertebrate food supplies and diet of blue duck on rivers in two regions of the North Island, New Zealand , 1991 .

[11]  John A. Wiens,et al.  The Ecology Of Bird Communities , 1989 .

[12]  J. Eldridge.  Observations on a pair of Torrent Ducks , 1986 .

[13]  P. Krausman,et al.  Clarification of a technique for analysis of utilization-availability data , 1984 .

[14]  M. Winterbourn.  The river continuum concept — reply to Barmuta and Lake , 1982 .

[15]  K. Cummins,et al.  An Introduction to the Aquatic Insects of North America , 1981 .

[16]  Clyde W. Neu,et al.  A TECHNIQUE FOR ANALYSIS OF UTILIZATION- AVAILABILITY DATA' , 1974 .

[17]  S. Coscarón.  Claves para la identificacion de las especies de simúlidos del género Gigantodax (Insecta, Diptera, Simuliidae) en la Argentina y su distribución geográfica , 1971 .

[18]  P. Johnsgard.  The biology and relationships of the Torrent Duck , 1966 .