One of the 10 ducks on WAnimals
Birds · Anseriformes · Anatidae
Brazilian Merganser
Mergus octosetaceus
It faces an extremely high risk of imminent extinction in the wild. See full glossary
A slender, dark diving duck with a glossy dark green head topped by a long crest, shorter and more worn in females. Dark grey upperparts, a pale grey breast fading to a whitish belly, and a white wing speculum very visible in flight. Its bill is long, fine and black, with a serrated, tooth-like edge.
Weight
1.1 kg – 1.4 kg
Size
49 cm – 56 cm
Diet
Piscivore
Feeds mainly on fish.
Activity
Diurnal
Active mainly during the day.
Social structure
In pairs
Usually lives in pairs, sometimes for life.
Sighting difficulty
Very hard
Estimated population
Between 150 and 250 mature individuals; possibly fewer than 250 birds in the wild
Fun facts
- It is one of the six most threatened waterbirds in the world.
- It depends on pristine rivers: deforestation, mining, hydroelectric dams, pollution and even recreational canoeing degrade its habitat.
- Captive breeding began in 2011, when the Zooparque at Itatiba, in Brazil, raised the first ducklings; Prague Zoo joined in 2023 and had its first ducklings in 2025.
Life cycle & biology
- Skeleton type
- Vertebrate - internal bony skeleton (bird)
- Habitat & environment
- Isolated stretches of clear, fast-flowing rivers in Brazil, Argentina and Paraguay. It nests in tree hollows or rock crevices near the banks. Each pair uses an average of 9 km of river, an enormous home range compared with other Mergus
- Birth weight
- Precocial: born covered in down and leaves the nest within a few hours
- Size at birth
- Precocial: born covered in down and leaves the nest within a few hours
- Sexual maturity
- 2 years
- Gestation / incubation
- ~33 days of incubation
- Litter / clutch size
- 2 to 4 chicks per brood, averaging 2.7: lower than in other species of the genus
Sources consulted: IUCN Red List; Silveira y Bartmann 2002, Bird Conservation International (Serra da Canastra); Eyton 1838; Partridge (observaciones en Argentina, 1949-1954); Vieillot 1817; Threatened Waterfowl Specialist Group; Prague Zoo
Where to find it
See its range on the interactive mapBest time: All year round, though it is extremely elusive and hard to see
Where to watch it
Parks and dive sites where this species has been documented.
Related species
Other species in the catalogue with the most in common with Brazilian Merganser — same habitat, park, country, tags or family.
Knob-billed Duck
Sarkidiornis melanotos
White-faced Whistling-Duck
Dendrocygna viduata
Black-necked Swan
Cygnus melancoryphus
Southern Screamer
Chauna torquata
Jabiru
Jabiru mycteria
How to help
The brazilian merganser is classified as critically endangered. Organizations such as UICN, WWF y Wildlife Conservation Society work specifically on its conservation and that of its habitat; looking into their programs is a good starting point if you want to get involved.
It's documented in 5 real protected areas — part of why protecting these places matters for its conservation.
Keep exploring
Based on what we already know about brazilian merganser.
Comments
Share an experience, a fun fact or a tip for seeing the brazilian merganser.
Be the first to comment.