|Species:|| Mergus octosetaceus|
The Brazilian merganser measures about 49-56 cm in lenght. A dark, slender bird with an iridescent dark green hood and a long crest (which is shorter in females). Upperparts are dark grey while the breast is light grey, getting paler toward the whitish belly. Wings have a white wing patch, which is noticeable in flight. Legs are short and red, while the bill is thin, black and jagged.
Brazilian mergansers nest in tree cavities, rock crevices, or disused burrows predominantly made by armadillos. It is thought the breeding season is during the austral winter, when rain is minimal and water levels are low, but it may vary geographically. The Brazilian merganser usually lays three to six eggs in June and July, with the chicks hatching during the following July and August. The young are capable of flight by September and/or October. Only the female birds incubate the eggs, but both parents care for the young. This is a very unusual behavior in ducks for both parents to help raise the young birds including direct provision of food to young. Adult Brazilian mergansers are believed to remain on the same territory all year round, but there is not very much information about their movements and dispersal, so information on this is presently speculative in nature. Fish is the Brazilian merganser's main food, and they also eat molluscs, insects and their larvae. The birds, usually in pairs, capture fish by diving in river rapids and backwater. 
The Brazilian Merganser (Mergus octosetaceus) is one of the most threatened waterfowl in the world and one of the most threatened birds in Americas. Its distribution is restricted to the center-south of Brazil, and parts of Paraguay and Argentina. The species inhabits clean rivers and streams, with rapids and still waters, bordered by forests and with fish abundance. Besides being naturally rare, it has been affected by several human activities that interfere directly or indirectly with its habitats. Until very recently, there was very little available information about Brazilian Merganser. Fortunately, in the last years, intense field studies have improved our knowledge about its habits, ecology and distribution. The information which has been arisen from these studies, although still basic, is helping the species conservation.In 2006, the Brazilian Ministry of Environment (MMA) published the Action plan for the Brazilian Merganser Conservation, a strategic document with guidelines for conservation actions in long term. In 2008, the Instituto Terra Brasilis started a project to mark and monitor Brazilian Merganser individuals using colour rings and radio transmitters in the Serra da Canastra region, state of Minas Gerais. We believe the coming results will lead to a major contribution to improve our knowledge about this species, in particular in its territoriality, migration and dispersal.