Habitat use and diet of the Torrent Duck (Merganetta armata) in Ucumarí Regional Park in the Central Andes of Colombia

Abstract

Between July 1993 and December 1994, we estimated the population size of the Torrent Duck at the Ucumarí Regional Natural Park, characterized its habitat, and described some aspects of its feeding habits and diet. We found seven pairs of adult birds along a 15 km transect of the Otún River which crosses the Park. Both the frequency of observation of the birds at some sites, and the repeated findings of feces suggest that the population size remained constant during the study period. Our focal observations of two pairs of adults allowed us to calculate a mean length for their home ranges of 1400 m. Differences in some descriptive variables among ranges indicate some flexibility of the species in its habitat requirements. Sites occupied by the ducks differed from unoccupied sites only in the visibility to the nearest river bend. The diet of the Torrent Duck, determined from examination of feces, was dominated by immature aquatic insects, particularly Trichoptera. Although the diet was similar in composition to that of Rainbow Trout caught in the river, the null hypothesis of complete niche overlap among these species was rejected; this discards the likelihood of interspecific competition for food between them.