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New map identifies risks, and potential sanctuaries, for Brazil’s diving duck

  • The Brazilian merganser, a duck that’s the mascot for the country’s waterways, is among the top 10 most threatened birds in the world, with only about 250 individuals left in the wild.
  • As part of conservation efforts, scientists have recently published a map showing the critically endangered species’ distribution in its remaining habitat, as well as identifying suitable new areas where it could thrive.
  • The map also highlights the threats to this bioindicator species that needs clear, pollutant-free water to survive; the main threat comes from the damming of rivers, which affects water flow and quality for the mergansers.
  • The researchers found 36 small hydropower plants planned for areas close to sites where the species lives, potentially impacting 504 square kilometers (196 square miles), or 4.1% of the total area suitable for the duck’s habitat.

The first signal of the day is the sun stretching steadily upward amid a gigantic sea of mountains. The mass of rock, forest and water is so huge that the horizon doesn’t seem to fit into the gaze of those walking along the web of dirt roads where gates open onto valleys and meadows. This region in southwestern Minas Gerais state, Brazil, is home to a veritable nursery of springs. There are so many headwaters here that scientists call the place an immense water reservoir. The main river that starts here in the Canastra Mountains is the São Francisco river. The region is also a complex mosaic of biodiversity, home to several species of fauna and flora found nowhere else on Earth.

One of these is the Brazilian merganser (Mergus octosetaceus), a duck that’s among the top 10 most threatened birds on the planet, and which, in 2018, was officially designated by the government as a symbol of Brazilian waters.

Field biologist Wellington Viana, one of the scientists who monitors the ducks here, says there are just over 200 individuals left in the wild. The IUCN, which lists the species as critically endangered, puts the global population at an estimated 250. “About 140 — the largest population in the world — live in Canastra Mountains National Park and its surrounding areas, always distributed along riverbanks, usually located above the waterfalls,” Viana says.

The Brazilian Merganser once ranged across several areas of the Cerrado grasslands and Atlantic Forest of Brazil, Argentina and Paraguay. Today, it’s found in only three regions of central Brazil: the Canastra Mountains or Alto Paranaíba, Chapada dos Veadeiros, and Jalapão. Each breeding pair requires a home range of at least 5 kilometers (3 miles) along a river.

“Since it is considered a charismatic species, the Brazilian merganser has been used as a banner to raise awareness for water conservation,” Viana says. “The community has promoted actions to address issues related to the preservation of the ecosystem with a focus on water resources.”

The merganser is a diving duck, dipping into backwaters and around rapids to catch fish. It has a thin beak that’s curved at the tip, unusual for a duck, which doesn’t allow it to venture into deep waters in search for food. Factors such as the expansion of farmland, increased pollution in waterways, changes in water flow and level caused by hydroelectric projects, and the silting of rivers and lakes have put heavy pressure on preserved areas, putting the species’ survival at risk. The Brazilian merganser is a demanding species, thriving only in habitats with pristine springs, without the slightest trace of pollutants or any kind of substance capable of impacting the environment. This is why it serves as a bioindicator of water quality.

Casca d’Anta, the first waterfall on the São Francisco River, in the Canastra Mountains. It lies inside a national park that is home to nearly two-thirds of the global population of Brazilian mergansers. Image by Felipe Abreu.

Conducting surveys to preserve the species

To assist in the conservation of the species, a team of 14 scientists from 12 different institutions, including universities, federal and state agencies, the private sector and NGOs, have joined forces to draw up a map of the most suitable areas for the Brazilian merganser — areas where the species has the best chance of survival due to environmental characteristics.

The resulting map that forms the heart of a recently published study was a collaboration by researchers from the National Center for Research and Conservation of Wild Birds (Cemave)/ICMBio, the IUCN Conservation Planning Specialist Group, and the University of São Paulo, among others. It was produced under the National Action Plan for the Conservation of the Brazilian Merganser.

By mapping the regions inhabited by the duck, the researchers established a parallel between the risk factors, highlighting plans for the construction of hydroelectric projects in areas where the species occurs, and possible actions to conserve the remaining populations. The national action plan shows there are 455 hydroelectric plants operating in Brazil, with 1,577 currently in the study phase for construction in the coming years. In the Cerrado, the only biome in Brazil that still hosts Brazilian mergansers, 128 hydropower plants are already in operation, with 625 more planned.

Study lead author Alex Bovo, from the University of São Paulo, says this method of the species distribution modeling is a tool for major conservation planning. “The group of experts provided data on the recent presence of the bird and, by using the tool, it was possible to point to the areas with the highest environmental adequacy for the duck,” he says.

With the map, it’s possible to direct the search for new populations, investigate potential threats to the species, and help to define areas for reintroduction, he says. “In addition, we quantified the potential impact of the construction of new small hydroelectric power plants, the use of land in the appropriate areas, and the adequate areas in which the species occurs and that are protected by conservation units, like national and state parks,” Bovo says.

The map developed by the authors of the study show the places where the Brazilian merganser was recently recorded (black dots) and the areas of environmental suitability (red), which are the habitats most favorable for the species’ survival. Image courtesy of Bovo et al. (2021).

Small hydroelectric plants pose a big threat

In the short term, the direct effects of human activity on the Brazilian merganser’s habitat are fish mortality, reduced water visibility, and erosion of river and lake margins. The study detected that 36 small hydropower plants (SHPs) planned for areas close to sites where the species lives. These SHPs could impact a combined area of 504 square kilometers (196 square miles), or 4.1% of the total area suitable for the duck’s habitat. There are other SHP projects planned within a 20-kilometer (12-mile) radius of locations where populations were recently recorded.

Most of the mergansers in the Canastra Mountains live in the Araguari River Basin, and the 11 SHPs planned for that region would put 18% of the global Brazilian Merganser population at risk. In the north of Goiás state, the construction of new SHPs could break the natural connectivity of rivers in the region, threatening the biodiversity of Chapada dos Veadeiros National Park.

Ornithologist Paulo Antas, from Fundação Pró-Natureza (Funatura), which also worked on the map, says hydropower development needs to be compatible with the protection of the species that symbolizes Brazil’s continental waters. “We have the technology to build SHPs according to the run-of-river model, without dams, which does not affect the river. There are ways to integrate development and nature conservation,” he says.

Antas says there’s been the alarming reduction of merganser populations in the region. In Chapada dos Veadeiros, he says, the best population estimates point to 45 mergansers. In Jalapão, a population count in August 2019 found 25 adults and eight ducklings. “Because it is rare and signals places where the environment is healthy, the Brazilian merganser is a primordial species for maintaining the quality of wildlife and human populations,” Antas says.

In general, the modeling results paint a worrying picture, conservationists say. They show there are few areas that are environmentally favorable as habitat for the Brazilian Merganser.

Brazilian Mergansers only lives in fast-flowing, clean rivers with no traces of pollution; for this reason, it is a bioindicator of water quality. Image by Adriano Gambarini.

“It is important to reiterate that this study doesn’t represent a rejection of the construction of SHPs,” Bovo says. “But it reinforces the importance of environmental licensing and the assessment of possible environmental impacts that must be minimized or mitigated. And also, whenever necessary, that other alternatives be employed, especially when we’re dealing with species whose numbers are so reduced in nature.”

The loss of habitat caused by dams has already been reported in Brazil, Argentina and Paraguay. In Argentina, the construction of the Urugua-í dam may have driven the local extinction of the Brazilian merganser. Although the impact of an SHP is much smaller than that of a conventional hydroelectric power plant, it causes enough changes in the water flow to affect a sensitive species.

“The shift of a lotic [running water] to lentic [still water] ecosystem after a dam flooding eliminates the ecological requirements of the Brazilian Merganser (e.g. clean and rapid water), an anthropogenic environmental change that has impacted or threatened many other species worldwide,” the study says. “The unpredictable and avoidable changes in rivers caused by dams will reduce the availability of new areas for young dispersing Brazilian Merganser. In a scenario of insufficient rapids and streams with clear water, it is unlikely that these individuals will be able to establish their own territories, which would ultimately increase the risk of extinction on a regional scale due to reduced recruitment in a given population.”

But the researchers say there’s still reason for hope. Co-authors Gislaine Disconzi and Marcelo Barbosa, from the Chapada dos Veadeiros Brazilian Merganser Project and the Tocantins Nature Institute (Naturatins), respectively, say the results point to the possibility of finding new individuals and populations of the species. Viana, the biologist, says that, in the Canastra Mountains, the work is focused on raising awareness among farmers who are gradually learning to manage the environment.

The preservation of springs and gallery and riparian forests located on farmland is one of the issues being debated. By protecting the springs, farmers also contribute to protecting the merganser’s habitat.

“The combined effort is starting to pay off,” Viana says. “There are farmers who now understand how important it is to surround the springs. In a period of drought, for example, those who don’t, notice that their neighbors who do manage to keep the springs flowing. Word of mouth has given way to reflection. Some even work to reforest the areas nearby the riverbanks.”


Bovo, A. A., Ferraz, K. M., Ribeiro, F., Lins, L. V., Barbosa, M. D., Previdente, F. H., … Silveira, L. F. (2021). Remaining suitable areas for the critically endangered Brazilian merganser (Mergus octosetaceus; Aves, Anseriformes) are threatened by hydroelectric power plants. Perspectives in Ecology and Conservation, 19(3), 329-337. doi:10.1016/j.pecon.2021.04.002

Banner image of a Brazilian merganser by Adriano Gambarini.

This article was reported by Mongabay’s Brazil team and first publishedhere on our Brazil site on July 29, 2021.