Brazilian merganser conervation in Brazil

In 2024, Prague Zoo became the only zoo outside Brazil to exhibit the critically endangered Brazilian merganser to visitors. Photo: Miroslav Bobek, Prague Zoo

The Brazilian merganser (Mergus octosetaceus) depends on fast-flowing rivers with crystal-clear waters. A visual predator, it hunts fish underwater and therefore requires excellent visibility and an abundance of prey. It nests in tree cavities, rock crevices or steep riverbanks, and thus seeks rivers bordered by riparian forests offering sufficient nesting opportunities. The species is strictly monogamous and highly territorial. According to local conservationists, each pair occupies and defends a specific stretch of river up to 17 kilometres long.

MERGANSERS UNDER THREAT

The Brazilian merganser was first described scientifically in 1817, but little was known about it until the 1990s. Only at the turn of the millennium was an isolated population discovered in Serra da Canastra National Park in the Brazilian state of Minas Gerais. In recent decades, additional individuals have been recorded in parts of the states of Goiás and Tocantins. A few sightings have been also reported from Paraguay and Argentina, although the current population size in those countries—if any birds remain there at all—is unknown. According to the IUCN, the global population is estimated at 200 to 250 individuals, but local conservationists are far more cautious, suggesting there may be as few as 50.

Because the Brazilian merganser has very specific habitat requirements, it is extremely sensitive to any disturbance or habitat loss. The main threats to its survival include the destruction of riparian forests, degradation of riverbanks and channels, river pollution, pesticide use on pastures and crops, the construction of hydroelectric dams, and poorly planned recreational and tourism activities.

Portrait of a Brazilian merganser. Photo: Antonín Vaidl, Prague Zoo
 

ACTION PLAN AND CONSERVATION BREEDING

To protect the species, the Action Plan for the Conservation of the Brazilian Merganser was launched in 2006 as a result of cooperation between the Brazilian Institute of Environment and Natural Renewable Resources (IBAMA) and the Chico Mendes Institute for Biodiversity Conservation (ICMBio). In 2011, ICMBio, together with the Museum of Zoology University of São Paulo (MZUSP) and partner organisations, implemented the Brazilian Merganser Captive Reproduction Project with the aim of safeguarding a strong genetic population to serve as a backup.

Captive breeding began in 2011, when eggs were collected in Serra da Canastra National Park in Minas Gerais. Two ducklings hatched and were successfully reared. Further egg collections were subsequently carried out under the Action Plan, with the eggs being transferred to Zooparque Itatiba, which in 2014 became the central facility for the emerging ex situ population (i.e. the population living under human care)..

Brazilian merganser at Zooparque Itatiba, Brazil—for a time the only institution keeping the species under human care. Photo: Antonín Vaidl, Prague Zoo
 

The world’s first breeding of Brazilian mergansers from parent birds living under human care took place at Zooparque Itatiba in 2017, when four ducklings were successfully hand-reared. The following year, another four hatched there—this time the eggs were incubated by the mother, and the ducklings were raised by their parents. This breeding success was of great importance for the project, as it showed that hand-reared birds retain their innate ability to care for their offspring. It therefore offers promising prospects for the planned reintroduction programme.

PRAGUE ZOO’S CONTRIBUTION

Prague Zoo joined the Brazilian merganser conservation programme in 2019. Initially, it provided technical support, financing the purchase of a generator for the incubators and rearing facilities at Zooparque Itatiba, as frequent power outages could otherwise have caused devastating losses—especially given the extremely small number of birds kept under human care. Prague Zoo has also contributed to the monitoring of wild mergansers by purchasing transmitters and providing a boat for the staff of the Natureza do Futuro association, which specialises in this species.

In October 2023, Prague Zoo elevated its involvement in the conservation of the Brazilian merganser to a new level when it received five pairs of this critically endangered species and became the centre of a developing European backup population. It was the first time in history that representatives of these exceptionally rare ducks had left their Brazilian homeland. They can be seen in the Bird Wetlands exhibit in the lower part of the zoo, and by the end of 2024, they had laid their first eggs. In early 2025, Prague Zoo celebrated the world’s first hatching of Brazilian merganser ducklings under human care outside Brazil.

Brazilian merganser ducklings at Prague Zoo—the first ever hatched under human care outside Brazil. Photo: Miroslav Bobek, Prague Zoo
 

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