Brazilian Merganser (Mergus octosetaceus)

Brazilian Merganser

[order] ANSERIFORMES | [family] Anatidae | [latin] Mergus octosetaceus | [authority] Vieillot, 1817 | [UK] Brazilian Merganser | [FR] Harle huppard | [DE] Dunkelsager | [ES] Pato Serrucho (Arg), Serreta Brasilena | [NL] Braziliaanse Zaagbek


Genus Species subspecies Region Range
Mergus octosetaceus SA e, sc


Mergus is the genus of the typical mergansers, fish-eating ducks in the seaduck subfamily (Merginae). The Hooded Merganser, often termed Mergus cucullatus, is not of this genus but closely related. The other “aberrant” merganser, the Smew (Mergellus albellus), is phylogenetically closer to goldeneyes (Bucephala). Although they are seaducks, most of the mergansers prefer riverine habitats, with only the Red-breasted Merganser being common at sea. These large fish-eaters typically have black-and-white, brown and/or green hues in their plumage, and most have shomewhat shaggy crests. All have serrated edges to their long and thin bills that help them grip their prey. Along with the Smew and Hooded Merganser, they are therefore often known as “sawbills”. The goldeneyes, on the other hand, feed mainly on mollusks, and therefore have a more typical duck-bill. They are also classified as “divers” because they go completely under-water in looking for food. In other traits, however, the genera Mergus, Lophodytes, Mergellus, and Bucephala are very similar; uniquely among all Anseriformes, they do not have notches at the hind margin of their sternum, but holes surrounded by bone.

Physical charateristics

Brazilian Merganser is a slender, dark, medium-sized bird, with a typically long crest on the rear of the head. Back and wings are grayish brown. Head and neck darker with metallic dark green reflections, better seen under sunlight. The breast is pale gray with narrow darker stripes; the color of the underparts becomes paler towards the abdomen. The wing white mirror is visible during flight and it is also commonly observed when the birds are resting or swimming. The head crest is longer in the males than females. The bill is thin, narrow and serrated.

Listen to the sound of Brazilian Merganser

[audio: Merganser.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 0 cm wingspan max.: 0 cm
size min.: 49 cm size max.: 56 cm
incubation min.: 33 days incubation max.: 35 days
fledging min.: 1 days fledging max.: 1 days
broods: 1   eggs min.: 5  
      eggs max.: 8  


South America : East, Southcentral. Mergus octosetaceus occurs in extremely low numbers at a few, highly disjunct localities in south-central Brazil. The strongholds are a recently discovered population on tributaries of the rio Sao Francisco in west Bahia, and in and (mostly) around Serra da Canastra National Park, Minas Gerais, where a total of 81 individuals was estimated.


The species inhabits clean rivers and streams, with rapids and still waters, bordered by forests or native vegetation, and with an abundance of fish. It is a shy bird and it is quite difficult to see in the wild. It prefers sparsely populated areas and avoids human presence, although at some localities it is bolder and occurs closer to villages and small towns. The Brazilian Merganser seems to tolerate some environmental degradation if there are well preserved stretches in its territory so the birds can seek shelter. Territory size of the Brazilian Merganser varies between 5 -12 km of rivers and streams in the Serra da Canastra region.


Brazilian Mergansers nest in holes of trees, and holes in rocks and in river banks. Nest site for Brazilian Merganser, in rock cavity. The entrance to the nest cavity is located from 2 to 25 m above the water. Only the female incubates, and she leaves the nest twice per day to feed. The male spends most time resting or feeding nearby, constantly vigilant, but sometimes flies off, departing the area for several hours. The female lays up to eight eggs, which are incubated for about 34 days. When leaving the nest, the female covers the eggs with her down feathers. The ducklings leave the nest in the following day after hatching. The ducklings are encouraged to abandon the nest by the mothers call. The family stays together all the time; the parents constantly keep the young between them. The parents provide the ducklings with fishes and invertebrates. They feed their young directly into their beaks, or they place caught fish in the water after shaking it in order the ducklings can catch it. After 10 days of life, young were observed fishing on their own, reducing the need for food provided by their parents. The young are able to perform short flies when they are around 2 months old. They generally stay with their parents about six months or even longer. Many young die in these first months of life.

Feeding habits

Brazilian Mergansers feed basically on small fish they capture during dives, although aquatic macroinvertebrates also contribute to their diet. Very often, before diving, they search for their prey swimming with just their heads submerged. Dives can last 15 to 20 seconds, and even 30 seconds in deeper pools. We have observed them catching insects flying around their heads. In the Serra da Canastra region, the most common fish species which serve as their food are lambaris and barrigudinho. Stomach content analysis of individuals from Misiones, Argentina, showed they ate lambaris, ciclids, catfish, virolito, larvae of Dobson flies and, probably, molluscs.

Video Brazilian Merganser


copyright: Josep del Hoyo


Recent records from Brazil, and particularly a recent northerly range extension, indicate that this species’s status is better than previously thought. Nevertheless, the remaining population is still extremely small and severely fragmented, and the perturbation, damming and pollution of rivers continue to cause declines. For these reasons, it is listed as Critically Endangered.
Perturbation and pollution of rivers results largely from deforestation, agricultural expansion and, in the Serra da Canastra area, diamond-mining. Previously, the species was thought to rely on gallery forest which, although protected by law in Brazil, has been cleared illegally throughout much of the species’s range. However, evidence suggests it will occur on unforested, undisturbed stretches of river through cerrado. Mining has ceased in the immediate area of its known range but there is no additional habitat for dispersing birds. Expanding agriculture and the construction of hydroelectric dams are considered the principal threats to the species. Dam-building has already caused severe declines across much of its range. Tourist activities result in river perturbation and have been recorded within known territories and inside national parks.
Brazilian Merganser status Critically Endangered


It is non-migratory and does not abandon the stretch of river where it establishes its territory

Distribution map

Brazilian Merganser distribution range map

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