The Brazilian merganser (Mergus octosetaceus) is a South American diving duck in the Mergus genus.

It is one of the most threatened waterfowl species in the world, with possibly fewer than 250 birds in the wild and a small number kept in captivity in Brazil It has a long thin jagged black bill with red feet and legs. Although females are smaller with a shorter bill and crest, both sexes are alike in color. The slender ducks range in size from as an adult. Young Brazilian mergansers are mainly black with white throat and breast.

The Brazilian mergansers are generally silent birds, but may make barking calls in certain situations. Four calls have been recorded. A harsh krack-krack acts as an alarm call emitted in flight. Males make a barking dog-like call, females make a harsh rrr-rrrr and the contact call is a soft rak-rak-rak. Ducklings give a high pitched ik-ik-ik.

Depending on the availability of suitable nesting and feeding sites, Brazilian merganser pairs occupy permanent territories of stretches of rivers.

Conservation

thumb|Brazilian merganser in Prague Zoo

The Brazilian merganser captive-breeding program is led by Itatiba Zooparque, a zoo in Itatiba, São Paulo state, Brazil. The first collected eggs of Brazilian mergansers hatched in captivity in this zoo in 2011 and in 2017, Itatiba Zooparque announced the successful breeding of the first generation in captivity. In 2020, they announced 15 new ducklings and for the first time, they had second-generation ducklings. For the first time, one female laid seven fertilized eggs and they all hatched. First five ducklings hatched in Prague in spring 2025.

==References==<!-- Bird Conservation International (2006) 16:145–154. -->

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  • BirdLife Species Factsheet
  • ARKive – images and movies of the Brazilian merganser (Mergus octosetaceus)
  • Brazilian Merganser on postage stamps