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Species Guide
A photo of a Brazilian Merganser (Mergus octosetaceus)
Brazilian Merganser

Brazilian Merganser

Mergus octosetaceus

The Brazilian merganser (Mergus octosetaceus) is a rare and striking South American diving duck. It is characterized by its dark, slender profile and a lustrous dark-green hood with a long crest, which tends to be shorter and more worn in females. The upperparts are a dark grey, contrasting with a light grey breast that fades to a whitish belly. In flight, a white speculum is particularly noticeable. The species sports a long, thin, jagged black bill, complemented by red feet and legs. Adult Brazilian mergansers typically measure between 49 to 56 centimeters in length. Juveniles are predominantly black with a white throat and breast.

Identification Tips

To identify the Brazilian merganser, look for its unique bill, which is long, sharp, and serrated, resembling a row of teeth. The males and females are similar in plumage, though females are slightly smaller with a shorter bill and crest. The white speculum on the wing is a key feature to look for, especially when the bird is in flight.


This species inhabits clean, fast-flowing rivers and streams, often surrounded by riparian vegetation in remote and mountainous regions. They are highly territorial, defending extensive stretches of river and adjacent land.


Once found across central-south Brazil, Paraguay, and Argentina, the Brazilian merganser's range has now contracted significantly. The most significant and well-known population resides in Brazil's Serra da Canastra region, with isolated populations hundreds of kilometers apart.


Brazilian mergansers are generally silent but may emit barking calls under certain circumstances. They are known to occupy permanent territories along rivers, where they nest in tree cavities, rock crevices, or abandoned burrows. Both parents are involved in rearing the young, which is an unusual behavior among ducks.

Song & Calls

The Brazilian merganser has a repertoire of four calls: a harsh "krack-krack" alarm call, a barking call by males, a harsh "rrr-rrrr" by females, and a soft "rak-rak-rak" contact call. Ducklings produce a high-pitched "ik-ik-ik."


Breeding likely occurs during the austral winter, with egg-laying in June and July and hatching in July and August. Chicks are flight-capable by September or October. The female incubates the eggs, but both parents care for the young, including providing food directly.

Diet and Feeding

The Brazilian merganser primarily feeds on fish, diving in river rapids and backwaters to catch its prey. They also consume molluscs, insects, and their larvae.

Conservation Status

The Brazilian merganser is classified as Critically Endangered, with fewer than 250 individuals believed to exist in the wild. Habitat degradation and loss due to human activities such as farming, mining, and dam-building pose significant threats to their survival. Conservation efforts are critical to prevent the imminent risk of extinction.

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