|Female (left) and male Colombian torrent duck, Cañón del Río Anaime, Colombia|
M. a. colombiana (Des Murs, 1845)
The torrent duck (Merganetta armata) is a member of the duck, goose and swan family Anatidae. It is the only member of the genus Merganetta. Today it is placed in the shelduck subfamily Tadorninae after the "perching duck" assemblage where it was formerly assigned to was dissolved because it turned out to be paraphyletic. Its closest relative may be the blue duck of New Zealand.
This 43–46-centimetre (17–18 in) long species is a resident breeder in the Andes of South America, nesting in small waterside caves and other sheltered spots. Like the blue duck, it holds territories on fast flowing mountain rivers, usually above 1,500 metres (4,900 ft). It is a powerful swimmer and diver even in white water, but is reluctant to fly more than short distances. It is not particularly wary when located.
Male torrent ducks have a striking black and white head and neck pattern and a red bill. In flight they show dark wings with a green speculum. Females of all subspecies are somewhat smaller than the drakes; they have orange underparts and throat, with the head and upperparts grey and a yellower bill. Juveniles are pale grey above and whitish below.
The male's call is a shrill whistle, and the female's is throatier whistle.
This is a declining species nowadays due to competition for its invertebrate food from introduced trout, pollution, forest destruction, and damming of mountain rivers for hydroelectric schemes. The Chilean population seems to be relatively stable, while the more northern ones are more seriously affected. However, the overall population is still large enough to warrant classification as a Species of Least Concern in the IUCN Redlist.
The subspecies taxonomy is quite confusing. Males of the southern nominate subspecies M. a. armata, the Chilean torrent duck, have a grey back and blackish underparts with a chestnut belly. Males of the slightly smaller northern subspecies, the Colombian torrent duck, M. a. colombiana, are paler underneath, with streaked grey-brown underparts. Males of a third subspecies, the Peruvian torrent duck, M. a. leucogenis, are intermediate but very variable in plumage; some have entirely black underparts (turneri morph). Only males of the Chilean torrent duck have a black 'teardrop' mark beneath the eye. The Peruvian torrent duck is sometimes split into not less than 4 subspecies (leucogenis, turneri, garleppi and berlepschi), but these are more likely simply color variations, as they are not limited to distinct areas.
Juvenile (left) and female Peruvian torrent duck on the Urubamba River, Peru
Male Chilean torrent duck near Fitz Roy, Argentina