Mergus octosetaceus
One of the most enigmatic of all ducks, the Brazilian merganser is also one of the most threatened birds in the world.
Appearance
Dark, medium-sized, slender duck with a distinctive long, shaggy crest and large broad tail, often held in cocked position. Head and neck dark glossy green, body grey-green with green and white barring on belly. White panel (speculum) in wing. Long thin serrated black bill. Red feet and legs. Both sexes are alike, although the female is smaller with a shorter bill and crest. Downy young mainly black with white throat and breast.
Distribution
The Brazilian merganser has a highly fragmented range centred on central-southern Brazil. A small remnant population remains in Misiones, north-east Argentina, and it formerly occurred in eastern Paraguay but has not been seen there for around 25 years. It occurs on only four watersheds - three in Brazil and one in Argentina/Paraguay.
Population size
The total number of known birds is around 200-250, but the population is likely to be larger (possibly 300-400) as there are a number of areas holding suitable habitat that have yet to be adequately surveyed. Nevertheless, the species remains extremely vulnerable, particularly as there is currently none in captivity. Numbers are believed to have decreased in recent decades, but information on historical numbers is lacking.
Threats
The principal threat is the peturbation and pollution of its riverine habitats, largely resulting from deforestation or selective logging, and agricultural expansion. Dam construction, forest fires and disturbance have also resulted in the loss of suitable habitat in some areas. Diamond mining has also been an important threat at the key site in Brazil, Serra da Canastra, but this is currently reduced. Hunting and specimen collection formerly a problem.
Habitat
Clear, fast flowing rivers and streams that flow through undisturbed areas of subtropical forest and grassland with gallery forest.
Breeding
Breeds during the austral winter, when rain is minimal and river levels are low. Nests are located in holes in trees, rock crevices or disused burrows predominantly made by armadillos. Clutches of around six-eight eggs are laid in June/July, with young hatching usually during July/August and capable of flight by September/October. Only the femail incubates eggs, but both parents care for the young, which includes direct provision of food to young - very unusual behaviour in ducks. Adults are thought to remain on the same territory all year round, but almost nothing is known about their movements and dispersal, so this currently remains informed speculation.
Food
Almost entirely fish-eating but also takes insect larvae and molluscs. Searches for fish by swimming with head submerged before diving to catch prey. Feeds also in deeper waters where exploratory dives may last up to half a minute.
Voice
Generally silent, but four calls recorded: a harsh krack-krack alarm call emitted in flight; a barking-dog-like call given by the male; a raucous rrr-rrrr given by the female; a soft rak-rak-rak contact call. Ducklings give a high pitched ik-ik-ik.
Help protect this species
Join WWT today.