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Version 1.0

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Brazilian Merganser Mergus octosetaceus

Ivana R. Lamas and Líiva V. Lins
Version: 1.0 — Published April 28, 2009


Mergus octosetaceus occurs in low numbers at a few, highly disjunct localities in South America. It is considered critically endangered globally by the IUCN (visited on 12 February 2009), in the Americas (Collar et al. 1992), as well as in Brazil (Portaria Ibama 1522/89).

BirdLife estimated there were only 50-249 individuals in the world (BirdLife International 2000). Recent records have been proved the population size is larger than it was supposed, although it is not possible to make a good estimate of its population size. Nevertheless, the remaining population is still extremely small and severely fragmented, and several threats continue to cause declines (BirdLife International).

Effects of human activity on populations

All anthropogenic activities that influence the quality and integrity of the rivers and their banks are a potential threat to the Brazilian Merganser. Here we highlight these factors based on Lamas (2006).

Brazilian Merganser occurs mainly in watercourses with riffles, pools and waterfalls. Changes in the hydrological regime, mainly due to the development of hydroelectric power plants, turn former long stretches of rivers into reservoirs, which has an extreme effect on some merganser populations. In the Serra da Canastra region, for example, the Furnas and Mascarenhas de Moraes dams flooded several kilometres of flowing water, wiping out habitats that certainly held several territories. There are several new such infrastructure projects under way in different areas of the distribution of the Brazilian Merganser. To date, the only record of a Brazilian Merganser in standing waters (De Paula et al. 2008) seems to represent no more than an occasional occurrence. The operations of mining companies also interfere in with water including at springs and headwaters, potentially bringing negative impacts to Brazilian Mergansers habitats.

The destruction of riparian forests, though forbidden by law, is a common practice. The effects of the removal of riparian vegetation lead to degradation of the banks and erosion and silting of watercourses. On most of cattle-raising farms where riparian forest still survives, the cattle are allowed to enter the vegetation to access the watercourses, which leads to the destruction of the undergrowth and compaction of the soil. We rarely find fences stopping the cattle from gaining access to the riparian forest. This vegetation, besides safeguarding the watercourses from adjacent anthropogenic activities, provides an important measure of isolation for the mergansers.

Domestic sewage, along with the pesticides used on pastures and crops, leaches into the drainage system and has become a major source of permanent pollution. Cultivation of crops sometimes extends as far as the river banks. The various roads that cross drainages also increase sediment transport to aquatic environments.

We do not have evidence of the depth of the impact of tourism activities on Brazilian Merganser populations. In the Serra da Canastra National Park the type of tourism developed thus far do not seem to interfere significantly with the Brazilian Merganser’s behavior, given that a pair has been breeding successfully over the years close to one of the most often visited areas in the park (Silveira and Bartmann 2001, Bartmann 1988, and personal observations). Nevertheless, there has been a significant increase in tourism, both in the park and in its vicinity. The ever-growing number of tourists who come looking for rivers and waterfalls could potentially interfere with the birds’ behaviour; this should be monitored closely.

Another potential, but very poorly studied, effect is the presence of exotic species of fish in the region. The Peacock Bass (Cichla sp.), along with other allochthonous species,  commonly are introduced into the reservoirs and water courses. The Peacock Bass is also very common in fish-and-pay ponds. Such predatory species have caused profound changes in the environments where they have been introduced, with the disadvantage that there are no effective processes to eradicate the species once it has settled in a host community (Fabio Vieira 2002, pers. comm.). Though the Peacock Bass prefers to inhabit mostly still-water environments, it is possible to find it in river stretches. Being an essentially fish-eating species, it may alter the dynamics of the native water communities as it becomes established. Small native fish make up the Brazilian Merganser’s basic source of food and any factor interfering with the supply may have serious consequences for its populations.

Hunting does not seem to be a current threat to the Brazilian Merganser. We heard stories, which we could not substantiate, that the species used to be hunted in the past. Some local inhabitants claimed that it is not advantageous to hunt the bird as it is difficult to approach and at the same time small and with very little meat. Yet, one has to take into account that the whole subject of “hunting” is mostly avoided by all and only rarely we find someone willing to provide positive information.

Recommended Citation

Lamas, I. R. and L. V. Lins (2009). Brazilian Merganser (Mergus octosetaceus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.bramer1.01