Justification of Red List Category
This species has a moderately small population and range. It is known from a limited number of disjunct sites of occurrence. Its range and population are thought to be declining because of continuing habitat destruction. About half of the original forest cover within its range has already been lost. Consequently, the species is listed as Near Threatened.
Its potential global population was estimated to be as high as 78,000 ±7,000 mature individuals based on estimates of the area of forest cover within its range. However, the two occupied areas in Colombia are 520 km apart. Although the species may occur in appropriate habitat in between these sites (Salaman and Stiles 1996, P. Salaman in litt. 1999, 2000, Renjifo et al. 2002, P. Salaman in litt. 2003), searches of the intervening area have completely failed to find the species, despite excellent knowledge of its vocalizations and its reliable response to playback (P. Salaman in litt. 1999, 2000, 2003). Therefore, a precautionary population size estimate was made of 15,600 ±1,400 mature individuals based upon a figure of 20% occupancy within the Extent of Occurrence (Jahn et al. 2007). The total population is estimated to number 20,000-25,000 individuals, based on population density data from Ecuador extrapolated over the species's known range. Population size is thought to be declining owing to loss and fragmentation of its habitat.
The species is thought to be in decline, but the rate of decline has not been assessed directly. A recent analysis of the deforestation rate in the Chocó area of northwestern Ecuador found that on average, 61% of the original forest cover has been lost (Finer and Mamani 2019, M. Schaefer in litt. 2019). Forest loss has been most severe in the lowlands, with 68% of the original forest cover gone. In mid and upper elevations, where Chocó Vireo is found, about 50% of the original forest cover has disappeared (Finer and Mamani 2019, M. Schaefer in litt. 2019). Between 2000 and 2018, deforestation rates in the Ecuadorian Chocó amounted to 20% (Finer and Mamani 2019, M. Schaefer in litt. 2019). There are no detailed data available for the rate of forest loss in the Colombian part of the range. While forest cover in western Colombia was stable overall, or even increasing between 2001 and 2010 (Sanchez-Cuervo and Aide 2013), it is feared that deforestation rates have increased since (M. Schaefer in litt. 2019). Therefore precautionarily, it is assumed that the overall forest cover throughout the range has declined by 20% between 2000 and 2018. Assuming furthermore that deforestation continues at the same rate and that the population decline is proportional to the deforestation rate, it is suspected that Choco Vireo is declining at 14.5% over three generations (12.6 years). To account for local differences in the rate of population decline, it is here placed in the band 10-19% over three generations.
Vireo masteri occurs in the Chocó region on the Pacific slope of the West Andes of Colombia and north-western Ecuador. It is known from few disjunct sites (Brewer 2018). In Colombia it is found in Alto de Pisones and Montezuma, Risaralda, and in the Junín area, Nariño (Salaman 1994, Salaman and Stiles 1996, P. Salaman in litt. 1999, 2000, 2003, Freeman et al. 2012). In Ecuador, it is known from Alto Tambo and El Cristal, Esmeraldas, and the Mashpi road, Pichincha (Jahn et al. 2007, D. Brinkhuizen in litt. 2010, Brinkhuizen and Solano-Ugalde 2012). Although it cannot be ruled out that Choco Vireo occurs in suitable habitat between these sites (Salaman and Stiles 1996, Renjifo et al. 2002), searches in intermediate areas so far have failed to find the species (P. Salaman in litt. 1999, 2000, 2003).
In Colombia, the species is restricted to wet (>5,000 mm precipitation per year) primary cloud-forest. It occurs between 1,200 and 1,600 m on steep slopes (Salaman and Stiles 1996, Renjifo et al. 2014, Brewer et al. 2018). It is often found in areas with abundant palms, epiphytes, ferns and moss (Salaman and Stiles 1996, P. Salaman in litt. 1999, 2000, 2003). In Ecuador, the species uses a wider range of habitats, including wet primary forest as well as forest edges bordering pastures, roads, railways and re-growth of intensively logged forest, on steep slopes or level ground (Jahn et al. 2007). In Ecuador, it occurs from 800 to 1,500 m (Jahn et al. 2007). In Colombia, up to five territorial singing males were encountered per kilometre of transect (P. Salaman in litt. 1999, 2000, 2003), whilst densities of 15.9 ±1.4 territories/km2 were estimated within suitable habitat in Ecuador (Jahn et al. 2007). Encountered in pairs, individuals and family parties, it primarily forages in the canopy, or occasionally lower down in clearings and tree-falls. It is often found accompanying mixed-species flocks (Salaman and Stiles 1996, P. Salaman in litt. 1999, 2000, 2003, Jahn et al. 2007). Breeding takes place during the dry season, from June to October, and adults have been seen feeding juveniles in August (Salaman and Stiles 1996). It is a very active forager, feeding on invertebrates (Salaman and Stiles 1996).
The range and population of Choco Vireo are in decline as a consequence of habitat destruction. The Chocó region has long been a source of timber, but logging has intensified since the mid-1970s. Plans to colonise and develop the region are progressing through infrastructural improvement, particularly the rapid expansion of the road network, and are increasing the impact of logging, small-scale agriculture and gold mining (Salaman 1994, Wege and Long 1995, Salaman and Stiles 1996). Coca cultivation is a growing problem particularly at lower altitudes (P. Salaman in litt. 1999, 2000, 2003). In Colombia, Río Ñambi Community Nature Reserve is threatened by logging and disputes over land ownership, but the population is currently secure (P. Salaman in litt. 1999, 2000, 2003). Alto de Pisones remains unprotected and largely deforested (P. Salaman in litt. 1999, 2000, 2003). In Ecuador, the species is presumed to occur within the Cotacachi-Cayapas Ecological Reserve in Esmeraldas (244,000 ha; altitudinal range 80-4,900 m). However, the reserve is threatened by incursions from local communities and colonists from Colombia and other regions of Ecuador (Jahn et al. 2007, O. Jahn in litt. 2007). Forests around Alto Tambo are largely unprotected and threatened by clearance for cattle ranching and forestry projects (Jahn et al. 2007, O. Jahn in litt. 2007).
Conservation Actions Underway
In Colombia, the species is protected in the Tatamá National Park (Freeman et al. 2012), Las Tangaras Nature Reserve, Chocó and El Pangan and Río Ñambí Community Nature Reserves, Nariño (Salaman and Stiles 1996, R. Strewe in litt. 1999, P. Salaman in litt. 1999, 2000, 2003, 2012). Although the population at Alto Pisones remains unprotected, the area may be included in the proposed Caramanta National Park, a management plan for which is in preparation (Stiles 1998). In Ecuador, populations may exist within the Cotacachi-Cayapas Ecological Reserve (Jahn et al. 2007). Some of the occupied area at Alto Tambo is protected as an extractive reserve by Fundación para el Desarrollo Forestal, indicating that the suitability of the area for this species may depend on future forestry practices (intensive vs. selective harvesting schemes; natural-forest management vs. plantations of exotic timber tree species) (Jahn et al. 2007). The species is listed as VU at national level in Colombia (Renjifo et al. 2014) and as EN in Ecuador (Freile et al. 2018).
10 cm. Small, olive-and-yellow, warbler-like bird. Olive-green above with broad, prominent yellow supercilium contrasting with greyish-olive crown and dark eye-stripe. Dark brown remiges with olive-green edges. Broad, creamy, double wing-bar. Creamy-white below, with yellow breast, flanks and vent. Blackish maxilla, pale mandible. Bright bluish legs. Similar spp. Brown-capped Vireo V. leucophrys has brown upperparts and lacks wing-bars. Rufous-rumped Antwren Terenura callinota has rufous rump and longer tail. Voice Variable, high-pitched, warbling song 6-20 notes over 1-3 seconds. Contact call brief dry chip, and disturbance note a nasal zhree-zhree-zhree, most similar to Red-eyed Vireo Vireo olivaceus in quality.
Text account compilers
Sharpe, C.J., Gilroy, J., Hermes, C., Benstead, P., O'Brien, A.
Brinkhuizen, D., Freile, J., Jahn, O., Salaman, P.G.W., Schaefer, H.M., Strewe, R. & Valenzuela, P.M.
BirdLife International (2021) Species factsheet: Vireo masteri. Downloaded from http://www.birdlife.org on 21/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/10/2021.