• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
This species is only known from a limited number of sites within a disjunct range. Its population is small, with very small, localised subpopulations which are suspected to be declining slowly in line with habitat loss and degradation. The species is therefore assessed as Near Threatened.

Population justification
Field surveys in the Tapichalaca Reserve, Ecuador, found the species to occur at a density of 1 individual/km² (Harris et al. 2008, Renjifo et al. 2014). Assuming that this density is representative for the entire range, and further precautionarily assuming that only 50% of forested habitat within the range is occupied (i.e. 50% of 11,000-12,000 km²; Global Forest Watch 2022), the total population may number 11,000-12,000 individuals. This is roughly equivalent to 7,300-8,000 mature individuals.

Trend justification
The population trend has not been quantified directly, but it is feared that the population is declining as a consequence of habitat loss within the range. Tree cover loss within the range is currently low (<2% over ten years; Global Forest Watch 2022, using Hansen et al. [2013] data and methods disclosed therein). Even though it may also be found in tall secondary forest and along natural gaps, the species is restricted to humid forest (Zimmer and Isler 2020), and thus population declines may be aggravated by additional habitat degradation. Nevertheless, it is unlikely that declines exceed 10% over ten years.

Dysithamnus occidentalis is known from a disjunct range from western Colombia through eastern Ecuador to northern Peru. The nominate subspecies occurs on the Pacific slope of the west Andes in Colombia (from Antioquia to Nariño) and possibly in Carchi, Ecuador. Subspecies punctitectus occurs on the eastern slope of the Andes in Napo, Morona-Santiago and Zamora-Chinchipe, Ecuador, to Cajamarca, Amazonas and San Martín, Peru. The species is however not well known, and may be found to have a wider and more continuous distribution than currently known.

It occurs in the understorey of wet montane primary forest mainly above 900 m, and up to 2,530 m (Harris et al. 2008, Zimmer and Isler 2020). Dense growth around tree falls, land slips or other light gaps is apparently preferred, but it has also 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 (Ágreda 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, and nests with nestlings found in undisturbed forest in November and December, while a juvenile was found accompanying two adults in August (Greeney 2002, 2004; Harris et al. 2008). The species' ecology is not well known.

The species 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 where large tracts of pristine forests are still present. However, 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. 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).

Conservation Actions Underway
The species occurs within several protected areas throughout its range, including Sumaco-Galeras National Park, Antisana Ecological Reserve, Cabañas San Isidro and Yanayacu Biological Station (Ecuador), as well as Tatamá, Munchique and Farallones the Cali national parks and in Tambito and Río Ñambi nature reserves (Colombia). It is listed as Endangered at the national level in Ecuador (Freile et al. 2019) and as Vulnerable in Colombia (Renjifo et al. 2014).

Conservation Actions Proposed
Conduct surveys around and between known sites to locate additional populations and to better delimit the distribution range. Investigate the species' ecology, behaviour, habitat requirements and dispersal abilities. Assess the species' tolerance of converted and disturbed habitats. Monitor the population trend. Monitor rates of habitat loss. 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.

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.

Text account compilers
Hermes, C.

Contributors
Greeney, H., Isherwood, I., Khwaja, N., Pople, R., Salaman, P.G.W., Sharpe, C.J., Stiles, F.G., Strewe, R., Stuart, T., Symes, A., Sánchez-Nivicela, M. & Ágreda, A.

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Recommended citation
BirdLife International (2024) Species factsheet: Bicolored Antvireo Dysithamnus occidentalis. Downloaded from https://datazone.birdlife.org/species/factsheet/bicolored-antvireo-dysithamnus-occidentalis on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 23/12/2024.