BirdLife species factsheet for Pale-throated Barbet: http://datazone.birdlife.org/species/factsheet/pale-throated-barbet-gymnobucco-vernayi
Endemic to highlands of west-central Angola, Pale-throated Barbet (Gymnobucco vernayi) was until recently considered conspecific with Naked-faced Barbet (G. calvus) (del Hoyo et al. 2018). Its habitat is described as similar to that of G. calvus (del Hoyo et al. 2018), and so it likely occurs in primary forest, as well as into secondary areas adjacent to such forest, as well as wooded grasslands and pastures (del Hoyo et al. 2002). As such, habitat loss – particularly the loss of nesting and roosting trees (del Hoyo et al. 2018) – is considered to be the key threat to the species.
The species is currently listed as Least Concern (BirdLife International 2018), but there have been noted declines including at Mt. Moco, where it has potentially gone extinct, and in Kumbira Forest (M. Mills in litt. 2018). Given its restricted range, and these observed declines we have therefore taken the opportunity to review the species’s status here against all criteria.
Criterion A – Extrapolating data from Tracewski et al. (2016) suggests that the area of forest within the species’s range is declining at a rate of approximately 8.6% over three generations (25.5 years). Therefore, if we assume that population trends are proportional to habitat trends, we can infer that the population is declining at a suspected rate of 8.6% over three generations. Survey work has shown the species to have disappeared from or declined at some locations (M. Mills in litt. 2018), which further supports the view that the species is in decline. However, a suspected rate of decline of 8.6% over three generations does not approach the threshold for Vulnerable under this criterion (30%), and even if we assume that the species is more susceptible to habitat loss and fragmentation, it is still unlikely that overall declines are at such a rate. As such, the species is considered Least Concern under Criterion A.
Criterion B – The species’s Extent of Occurrence is 38,600km2. Its Area of Occupancy has not been directly calculated, but the area of forest within its range, as calculated per Tracewski et al. (2016) is 10,900km2. Both of these values are too large to warrant listing under Criterion B. As such, the species is considered Least Concern under this criterion.
Criterion C – Up to now, the population size of this species has not been estimated. It was relatively frequently observed during the surveys of Mills et al. (2013), but from these observations we cannot calculate a global density estimate.
The species is considered to be in decline (although we can only suspect an overall rate), and it should likely be considered to be in one subpopulation per IUCN definitions (IUCN Standards and Petitions Subcommittee 2017). Therefore, the population size is key to whether the species warrants listing under this criterion. A population size of <15,000 mature individuals would mean the species warrants listing as Near Threatened, while a population size of <10,000 mature individuals would mean it warrants listing as Vulnerable. Assuming that only a proportion of its mapped range is occupied, density estimates would have to be <c.2.0 mature individuals/km2 to trigger a listing as Near Threatened, and <c.1.3 mature individuals/km2 to trigger a listing as Vulnerable under Criterion C2a(ii). Are these estimates plausible? If not, the population size of the species would be too large for listing under this criterion.
Criterion D – The species’s population size and range are too large to warrant listing under this criterion, and the species is assessed as Least Concern under Criterion D.
Criterion E – To the best of our knowledge, there has been no quantitative analysis of extinction probability conducted for this species. Therefore, it cannot be assessed against this criterion.
Therefore, we request any further information regarding population size estimates to see whether the species would warrant listing as Vulnerable or Near Threatened under Criterion C2a(ii). In the absence of any further information the species may warrant retaining as Least Concern. Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested.
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
BirdLife International. 2018. Species factsheet: Gymnobucco vernayi. Downloaded from http://www.birdlife.org on 27/11/2018.
del Hoyo, J.; Collar, N.; Kirwan, G. M. 2018. Pale-throated Barbet (Gymnobucco vernayi). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/467447 on 26 November 2018).
del Hoyo, J.; Elliott, A.; Sargatal, J. 2002. Handbook of the birds of the world, Vol 7: Jacamars to Woodpeckers. Barcelona, Spain: Lynx Edicions.
IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
Mills, M. S. L.; Melo, M.; Vaz, A. 2013. The Namba mountains: new hope for Afromontane forest birds in Angola. Bird Conservation International 23: 159-167.
Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.