Torrent ducksTorrent Duck (pair, male on left), Merganetta armata armata, Chile.

Ducks, it has to be said, may not be the most interesting of birds. With a few exceptions they are all rather alike in general body shape and behaviour, generally conforming to the familiar visage of a farmyard duck (this being a descendent of the Mallard).

Not so the truly remarkable Torrent Duck! This extraordinary bird occurs in fast-flowing streams and rivers of South America, where pairs occupy – and vigorously defend – linear territories. As if they were made out of rubber, these ducks throw themselves into the most tumultuous of rapids with wild abandon, bobbing about fearlessly in search of caddis fly larvae and other invertebrate prey. Most food, however, is taken in eddies and vegetated fringes. The pair invariably swim and feed together, hauling themselves up onto slippery boulders where they keep a constant look-out for rivals. If a rival appears, there is much energetic chasing, accompanied by head-bowing and tail-cocking displays.

My first encounter with one of these striking ducks was in Peru on a small mountain stream rushing beneath mossy forest on the fabled Manu Road that snakes its way down the eastern slopes of the Andes, from the altiplano to the Amazon. I’d been walking down the road, following a mixed flock of tanagers and other insectivorous birds, when I came to a small bridge. Perched on the bridge post was a tiny little flycatcher with a dark head – a Torrent Tyrannulet. As this little sprite flitted out across the water, its namesake – a male Torrent Duck – peered up at me briefly, then slid quietly off its boulder perch to disappear beneath the froth and bubbles. It was a fleeting observation, but memorable.

Later, still in Peru, I was to get much better views of these ducks along the spectacular Urubamba River which divides the little tourist town of Aguas Calientas from the former Inca citadel of Machu Picchu. Here I was able to watch fearless Torrent Ducks swimming, feeding and engaged in territorial disputes in the chilly waters that flow from the snow-capped Andean peaks.

Torrent Ducks in the Urubamba River Peru

Torrent Ducks, Urubamba River, Peru.

Underwater, I suppose these tough little ducks swim much like cormorants, propelling themselves with their webbed feet and with neck outstretched. Interestingly, the stiff tail feathers are evidently used in a similar manner to those of woodpeckers in that they help to provide balance on the smooth boulders. Underwater, the tail is no doubt used as a rudder.

There are six regional subspecies of Torrent Duck (Merganetta armata), with the males being quite different in plumage, but the rufous and grey females being more or less identical. The male of the northernmost subspecies (Venezuela to N.Ecuador – M. a. colombiana) has pale underparts with black streaks, while the male of the southernmost subspecies (the nominate M.a. armata occupies most of Chile and southern Argentina to Tierra del Fuego) has black chest and flanks with a cinnamon underbelly; this is the form in my illustration above.

Duncan Butchart

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