Brazilian Merganser Mergus octosetaceus occurs at a few highly disjunct localities in south-central Brazil, with a few records from Argentina in 2002 (the first in the country for 10 years despite extensive surveys) (Benstead 1994, Hearn 1994, J. C. Chebez in litt. 1999) and it was suspected to be extirpated from Paraguay, although local reports indicate that a few individuals may still survive (R. P. Clay in litt. 2003). It is currently listed as Critically Endangered under criterion C2a(i) because it has an extremely small and severely fragmented population, and the perturbation, damming and pollution of rivers continue to cause declines.
However, recent records indicate that this species’s status is better than previously thought. In 2001-2002, surveys around Serra da Canastra National Park, Minas Gerais, estimated a total of 81 individuals (Lamas 2006), but surveys conducted since then have yielded a rough estimate of 65-100 territories, roughly equivalent to 130-200 individuals (L. V. Lins unpubl. data). From the field surveys, it is believed that this number could even reach 100 territories (L. V. Lins unpubl. data) and if confirmed, would represent a significant increase to the size of the largest known subpopulation. During 2008-2011, individuals of this species were recorded in the municipality of Patrocínio, state of Minas Gerais (Brazil) (I. Lamas in litt. 2012); approximately 110 km further north from the Canastra northernmost records, suggesting that the Canastra population is more widely distributed (and consequently bigger) than previously thought (L. V. Lins in litt. 2012). In 2002, a small population was discovered on the rio Novo, in Jalapão State Park, Tocantins (Braz et al. 2003), and six expeditions in 2007 and 2008 surveying a c.55-km stretch of the rio Novo located three breeding pairs (Barbosa and Almeida 2010).
Although threats to this species have continued, knowledge of its occurrence has increased and with these new findings, the global population is said to be higher than 250 mature individuals, and the largest subpopulation greater than 50 mature individuals (L. V. Lins in litt. 2012). If this information is confirmed, this species would no longer qualify as Critically Endangered and would warrant downlisting to Endangered under criterion C2a(i) of the ICUN Red List, on the basis that the global population is <2,500 mature individuals and all subpopulations are ≤250 mature individuals, undergoing a continuing decline.
Information is requested on this species’s global population size, distribution, trends and size of the largest subpopulation. Additional comments on the proposed downlisting are also welcome.
Barbosa, M. O. & Almeida, M. L. (2010). Novas observações e dados reprodutivos do pato-mergulhão Mergus octosetaceus na região do Jalapão, Tocantins, Brasil. Cotinga 32: 40-45.
Benstead, P. (1994) Brazilian Merganser in Argentina: going, going. Cotinga: 8.
Braz, V. S., Abreu, T. L. S., Lopes, L. E., Leite, L. O., Franca, F. G. R., Vasconcellos, M. M. and Balbino, S. F. (2003) Brazilian Merganser Mergus octosetaceus discovered in Jalapao State Park, Tocantins, Brazil. Cotinga 20: 68-71.
Hearn, R. (1994) The current status of the Brazilian Merganser Mergus octosetaceus in Argentina. IWRB Threatened Waterfowl Research Group Newsletter: 14-15.
Lamas, I. R. (2006) Census of Brazilian Merganser Mergus octosetaceus in the region of Serra da Canastra National Park, Brazil, with discussion of its threats and conservation. Bird Conservation International 16: 145-154.
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