Justification Recent records from Brazil, and particularly a recent northerly range extension, indicate that this species's status is better than previously thought. Nevertheless, the remaining population is still extremely small and severely fragmented, and the perturbation, damming and pollution of rivers continue to cause declines. For these reasons, it is listed as Critically Endangered.

Family/Sub-family Anatidae

Species name author Vieillot, 1817

Taxonomic source(s) SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996)

Identification 49-56 cm. Dark, slender duck with long crest. Dark hood with petroleum-green sheen. Pale grey breast finely vermiculated dark, paler towards whitish belly. Dark grey upperparts. White wing speculum. Long, dark saw-bill. Pinky-lilac legs. Long, bushy hindcrest usually worn and shorter in females. Similar spp Neotropic Cormorant Phalacrocorax brasilianus is larger and darker with hooked bill. Voice Harsh and dry jrrec contact call. Also louder nasal juac calls. Hints Hides under overhanging vegetation.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

50-249

decreasing

32,600 km²

No

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: It inhabits shallow, fast-flowing rivers, requiring rapids and clear waters. It occurs especially in the upper tributaries of watersheds but ranges into small rivers with patches of gallery forest surrounded by cerrado or within Atlantic Forest. It is non-migratory and does not abandon the stretch of river where it establishes its territory²⁰. Pairs have used 8-14 km stretches of river^3,10. It nests in tree-cavities and rock-crevices^11,17. Breeding has been recorded in June-August^17,19, but timing may vary geographically. Young birds have been observed in August-November^17,19. The diet comprises fish, small eels, insect larvae, dobson flies (Corydalis sp.) and snails. In Serra da Canastra it eats mainly lambari Astyanax fasciatus. Territory size is believed to be related to the number of rapids, edgewaters, water speed, fish abundance and conservation of riparian vegetation²⁰.

Threats Perturbation and pollution of rivers results largely from deforestation, agricultural expansion and, in the Serra da Canastra area, diamond-mining^2,3. Previously, the species was thought to rely on gallery forest which, although protected by law in Brazil, has been cleared illegally throughout much of the species's range. However, evidence suggests it will occur on unforested, undisturbed stretches of river through cerrado. Mining has ceased in the immediate area of its known range but there is no additional habitat for dispersing birds¹⁰. Expanding agriculture and the construction of hydroelectric dams are considered the principal threats to the species¹³. Dam-building has already caused severe declines across much of its range. Tourist activities result in river perturbation and have been recorded within known territories and inside national parks²¹.

Conservation measures underway The species is legally protected in all three range states. It occurs in three Brazilian national parks, two state parks and one Reserva Particular do Patrimônio Natural (RPPN)¹³, although there are no recent published records from Emas National Park. A species action plan has been published which outlines in detail its current status, ecology, threats and proposed conservation actions²¹. In Argentina, sections of the Arroyo Uruzú are protected within the Uruguaí Provincial Park¹⁵. Regular monitoring of the population in Serra da Canastra National Park is conducted and in 2008 a team from the WWT and Terra Brasilis colour-ringed 14 individuals in the park and fitted five of them with radio transmitters increase knowledge of the species's movements and ecology^13,22. During one phase of a long-term study in Serra da Canastra National Park four pairs fledged 70 young in five years, representing a considerable contribution to the species's long-term survival and highlighting the importance of the park¹⁹. A Brazilian Merganser Recovery Team has been established with the aim of developing an action plan for its recovery¹⁸. There is a proposal to extend the boundaries of Chapada dos Veadeiros National Park to incorporate the newly discovered population in the rio das Pedras¹⁸. The WWT continues to raise funds for this species, and over the next 12 months hopes to continue monitoring and ecological research, develop education work to address the threats faced by the species and carry out a feasibility study for the development of a captive population²³.

Conservation measures proposed Assess the status of the Tibagi, Arroyo Uruzú and Novo populations¹⁰. Continue to monitor the Serra da Canastra population. Develop and implement a fieldwork strategy using satellite images. Protect the watershed and riverine habitats of populations, especially in Bahia. Install nest-boxes for populations outside Serra da Canastra National Park. Improve local awareness and promote riverbank protection. Conduct surveys in Paraguay to confirm local reports. Advocate for the expansion of the Chapada dos Veadeiros National Park in Brazil to include the newly discovered population in the rio das Pedras¹⁸. Considered captive breeding.

References Collar et al. (1992). 1. Anjos et al. (1997). 2. Bartmann (1994). 3. Bartmann (1996). 4. Benstead (1994). 5. A. Bosso and G. Gil per J. C. Chebez in litt. (1999). 6. Hearn (1994). 7. Pacheco and Fonseca (1999). 8. Pineschi and Yamashita (1999). 9. Silveira (1998). 10. L. F. Silveira in litt. (1999). 11. C. Yamashita in litt. (2000). 12. Bosso and Gil (2003). 13. Braz et al. 2003. 14. R. Clay in litt. (2003). 15. P. Benstead verbally (2004). 16. Arvelino de Paula (2008). 17. Lamas and Santos (2004). 18. Bianchi et al. (2005). 19. Bruno et al. (2006). 20. Lamas (2006). 21. Ibama (2006). 22. WWT (2008). 23. Anon (2009).

Further web sources of information

Fully detailed species account from the Threatened birds of the Americas: the BirdLife International Red Data Book (BirdLife International 1992). Please note, taxonomic treatment and IUCN Red List category may have changed since publication.

Recuento detallado de la especie tomado del libro Aves Amenazadas de las Americas, Libro Rojo de BirdLife International (BirdLife International 1992). Nota: la taxonomoía y la categoría de la Lista Roja de la UICN pudo haber cambiado desde esta publicación.

Text account compilers Phil Benstead (BirdLife International), Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Rob Calvert (BirdLife International), David Capper (BirdLife International), Rob P Clay (BirdLife International), Juan Mazar Barnett (Museo Argentino de Ciencias Naturales), John Pilgrim (BirdLife International), Andy Symes (BirdLife International)

Contributors Andrés Bosso (Aves Argentinas/AOP), J. C. Chebez, Rob P Clay (BirdLife International), G. Gil, Luís Fábio Silveira (University of São Paulo), Carlos Yamashita

IUCN Red List evaluators Stuart Butchart (BirdLife International), Rob Calvert (BirdLife International), Andy Symes (BirdLife International)

Recommended citation BirdLife International (2010) Species factsheet: Mergus octosetaceus. Downloaded from http://www.birdlife.org on 30/7/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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