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Bicoloured Antvireo Dysithamnus occidentalis
BirdLife is updating this factsheet for the 2016 Red List
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This species has a small range and fragmented distribution in which habitat continues to decline. It is also rare, and thus its population is suspected to be small, with very small, localised subpopulations likely to be declining in line with habitat loss. It therefore qualifies as Vulnerable.

Taxonomic source(s)
SACC. 2006. A classification of the bird species of South America. Available at: #

Thamnomanes occidentalis Stotz et al. (1996)

15 cm. Dark above and paler below, stocky antbird. Male is slaty-black above, paler below. Brownish-black wings with two white-dotted wing-bars. Concealed interscapular patch. Female has chestnut crown, chestnut-brown back, dusky wings and tail. Two buff-dotted wing-bars. Small white shoulder patch. Slaty-grey underparts, sides of head and eyebrow with fine whitish shaft-streaks. Olive-brown belly. Juveniles resemble female in plumage: chestnut in upperparts especially on crown and forehead, slaty grey underparts with flanks and lower belly olive-brown or chestnut and lacking concealed dorsal patch. Similar spp. Male Uniform Antshrike Thamnophilus unicolor lacks white in wing. Female T. unicolor has grey face and ochraceous-brown underparts. Voice Low-pitched, throaty scold of 2-4 rapid-burst syllables, JEER-deer-dur or JEER-deer-dur-dr, repeated at a rate of c.1 per second. Also short, low, uninflected whistled peeur. Possible song described as du-du-du-duAYY.

Distribution and population
Dysithamnus occidentalis has been recorded from four regions of the Andes in south-west Colombia, from one region in north Ecuador, and from at least four regions in east Ecuador (Collar et al. 1992, Whitney 1992, Krabbe and Palacio 1999, Ágreda et al. 2005, Harris et al. 2008). The nominate subspecies occurs on Pacific slope of the west Andes (Valle del Cauca, Cauca and Nariño), Colombia, particularly in Munchique National Park and surrounding areas, and there is a single record presumably of this subspecies from the west slope in Carchi, Ecuador (Krabbe and Palacio 1999, Ridgely and Greenfield 2001). In Ecuador the subspecies punctitectus occurs in the eastern cordillera of the Andes, mainly on the east slope (Napo and Morona-Santiago) and has recently been found as far south-east as the Cordillera del Cóndor, Morona-Santiago (Ágreda et al. 2005). The species may occur as far south as the south-eastern slope of the Cordillera del Cóndor, Cajamarca, north Peru (Schulenberg et al. 2007, Harris et al. 2008). It is generally rare, although it has been found at reasonable densities on Volcán Sumaco, Ecuador. It is likely to be declining in numbers.

Population justification
The population is estimated to number 2,500-9,999 individuals based on an assessment of known records, descriptions of abundance and range size. This is consistent with recorded population density estimates for congeners or close relatives with a similar body size, and the fact that only a proportion of the estimated Extent of Occurrence is likely to be occupied. This estimate is equivalent to 1,667-6,666 mature individuals, rounded here to 1,500-7,000 mature individuals.

Trend justification
This species's population is suspected to be declining rapidly, in line with rates of habitat loss within its range.

It occurs in the understorey of wet montane forest mainly above 900 m, and up to 2,800 m (Harris et al. 2008). Dense growth around tree falls, land slips or other light gaps is apparently preferred, but it has been observed in fragmented woodlots and in mature secondary palm forest in the vicinity of primary forest (Donegan and Dávalos 1999, R. Strewe in litt. 1999). It forages on or near the ground for arthropod prey, sometimes accompanying small understorey flocks (Agreda et al. 2005, Harris et al. 2008). The nesting biology has only been studied in north-east Ecuador, where nest-building is reported in March and October, incubation in November (Greeney 2004, Harris et al. 2008), and nests with nestlings found in undisturbed forest in November and December (Greeney 2002, Harris et al. 2008), while a juvenile was found accompanying two adults in August (Harris et al. 2008).

It has suffered substantial habitat loss to agriculture, especially in Ecuador, where much suitable habitat has been cleared, except on the Cordillera de Guacamayos and Volcán Sumaco. Even these areas are being encroached upon gradually, notably by families growing naranjilla. In Colombia, Munchique National Park and adjacent Tambito Nature Reserve are threatened by human settlement, and the construction of a hydroelectric plant. Widespread deforestation on the west slope in Nariño has left La Planada Nature Reserve largely isolated (Wege and Long 1995). At altitudes below 2,000 m, south-west Colombia has been transformed by logging, mining and conversion to livestock-farming and crop plantations (Salaman and Stiles 1996, P. G. W. Salaman in litt. 1999, 2000), notably coca (Anon. 2000).

Conservation Actions Underway
The Volcán Sumaco area is within Sumaco-Galeras National Park, Napo, which protects a large area of pristine habitat above 1,000 m. Remaining forest on the Cordillera de Guacamayos is part of the Antisana Ecological Reserve (Best et al. 1996). The privately protected forests of Cabañas San Isidro and the Yanayacu Biological Station near Cosanga (Napo) are known to protect a breeding population (Greeney 2002, 2004, Harris et al. 2008). Most Colombian sites are within or close to protected areas: La Planada Nature Reserve, in Nariño (F. G. Stiles in litt. 1999); Munchique National Park and adjacent Tambito Nature Reserve, both in Cauca (Wege and Long 1995, Donegan et al. 1998, Donegan and Dávalos 1999, R. Strewe in litt. 1999), and Farallones de Cali National Park, in Valle del Cauca, which protects a large area of pristine forest (Wege and Long 1995, F. G. Stiles in litt. 1999). Conservation Actions Proposed
Conduct surveys in Los Farallones de Cali National Park (Wege and Long 1995), Munchique National Park (Renjifo et al. 2002) and other areas within its projected range. Increase the area of suitable habitat that has protected status. Ensure robust protection of existing protected areas, especially those threatened by human settlement and clearance of adjacent habitat. Lobby against the hydroelectric project in Colombia.

Related state of the world's birds case studies

Agreda, A.; Nilsson, J.; Tonato, L.; Roman, H. 2005. Range extension for, and description of the juvenile of, Bicoloured Antvireo Dysithamnus occidentalis punctitectus in Ecuador. Cotinga 24: 20-21.

Best, B. J.; Checker, M.; Thewlis, R. M.; Best, A. L.; Duckworth, W. 1996. New bird breeding data from southwestern Ecuador. Ornitologia Neotropical 7(1): 69-73.

Collar, N. J.; Gonzaga, L. P.; Krabbe, N.; Madroño Nieto, A.; Naranjo, L. G.; Parker, T. A.; Wege, D. C. 1992. Threatened birds of the Americas: the ICBP/IUCN Red Data Book. International Council for Bird Preservation, Cambridge, U.K.

Donegan, T. M.; Dávalos, L. M. 1999. Ornithological observations from Reserva Natural Tambito, Cauca, south-west Colombia. Cotinga 12: 48-55.

Donegan, T. M.; Dávalos, L.; Salaman, P. G. W. 1998. An ornithological expedition to Tambito nature reserve, Cauca, Colombia, Aug-Sept 1997.

Greeney, H. F. 2002. First description of the nest for the Bicolored Antvireo (Dysithamnus occidentalis), with notes on its behavior in eastern Ecuador. Ornitologia Neotropical 13: 297-299.

Greeney, H. F. 2004. Breeding behavior of the bicolored Antvireo (Dysithamnus occidentalis). Ornitologia Neotropical 15: 349-356.

Harris, J. B. C.; Carpio, R. L.; Chambers, M. K.; Greeney, H. F. 2008. Altitudinal and geographical range extension for Bicoloured Antvireo Dysithamnus occidentalis punctutectus in south-east Ecuador, with notes on its nesting ecology. Cotinga: 63-65.

Krabbe, N.; Palacio, J. 1999. Range extension of Bicoloured Antvireo Dysithamnus occidentalis in Ecuador. Cotinga 11: 48.

Renjifo, L. M.; Franco-Maya, A. M.; Amaya-Espinel, J. D.; Kattan, G. H.; López-Lans, B. 2002. Libro rojo de aves de Colombia. Instituto de Investigación de Recursos Biológicos Alexander von Humboldt y Ministerio del Medio Ambiente, Bogot, Colombia.

Ridgely, R. S.; Greenfield, P. J. 2001. The birds of Ecuador: status, distribution and taxonomy. Cornell University Press and Christopher Helm, Ithaca and London.

Salaman, P. G. W.; Stiles, F. G. 1996. A distinctive new species of vireo (Passeriformes: Vireonidae) from the Western Andes of Colombia. Ibis 138: 610-619.

Schulenberg, T. S.; Stotz, D. F. ; Lane, D. F.; O"Neill, J. P.; Parker III, T. A. 2007. Birds of Peru. Prnceton University Press, Prnceton, NJ, USA.

Wege, D. C.; Long, A. J. 1995. Key Areas for threatened birds in the Neotropics. BirdLife International, Cambridge, U.K.

Whitney, B. M. 1992. Observations on the systematics, behavior, and vocalizations of "Thamnomanes" occidentalis (Formicariidae). The Auk 109: 302-308.

Further web sources of information
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.

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.

Explore HBW Alive for further information on this species

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.

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Isherwood, I., Pople, R., Sharpe, C J, Stuart, T., Symes, A. & Khwaja, N.

Salaman, P., Stiles, F., Strewe, R., Greeney, H. & Ágreda, A.

Recommended citation
BirdLife International (2016) Species factsheet: Dysithamnus occidentalis. Downloaded from on 24/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 24/10/2016.

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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Additional resources for this species

ARKive species - Bicoloured antvireo (Dysithamnus occidentalis) 0

Key facts
Current IUCN Red List category Vulnerable
Family Thamnophilidae (Antbirds)
Species name author (Chapman, 1923)
Population size 1500-7000 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 7,600 km2
Country endemic? No
Links to further information
- Additional Information on this species