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A Study of Nesting Torrent Ducks in the Andes

Moffett, G.M. Jr. 1970.
A study of nesting Torrent Ducks in the Andes.
Living Bird, 9: 5–27 + 3 plates.

Abstract

This paper describes a study of the Torrent Duck (Merganetta armata), undertaken in Río Negro Province of Argentina from September to November 1968. The birds, about whose natural history little has been recorded, live in rapid mountain streams of the Andes, where they feed almost exclusively upon the larvae of stoneflies (Rheophila). Their adaptations to life in these rapid currents include a torpedo-shaped body, proportionally large feet, a long, stiff tail, and a narrow, flexible bill. They generally work upstream on feeding forays, and frequently remain underwater for 16 s or more. One female’s foraging dives averaged 12 s. Upstream locomotion on the water includes skittering across the surface using their tail as a sculling oar and their feet as paddles. They tend also to move upstream along the banks where the current is not as swift, and effectively use the reverse eddies and still waters behind boulders. I found 2 nests, one in a cavity formed by the roots of a Nothofagus tree along the bank 9 feet above water, the other in a crevice in a cliff 60 feet above the water. I kept the two pairs under close surveillance. The species is monogamous. Pairs maintained rather strict territories that encompassed about 0.6 mile of river for a pair, although most of their time was spent in a ⅓-mile stretch of river. Territorial behavior consisted of calls, bowing displays, and “mule kicks” both in the water and on boulders. The female generally left the nest for several hours in the morning and several more in the late afternoon. The male did not incubate, but remained in the territory and usually in attendance with the female when off the nest. One week separated the laying of the last three eggs in one nest. In both pairs the male displayed to entice the female to return to her nest. The incubation period of one of the nests was 43–44 d. In one of the 2 nests, the 2 chicks that hatched jumped to the water 60 feet below, landing on rocks on the bank. Both, unharmed, plunged into the water and began swimming with the parents.

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