Birdlife International factsheet for Yellow-bearded Greenbul
Yellow-bearded Greenbul is found in Africa, in a range that encompasses Guinea, Liberia, Côte d’Ivoire, and Ghana (BirdLife International, 2020). It inhabits the midstorey of lowland primary forest, and can also be found in mature secondary forest (Gatter, 1997). The total population for this species is estimated to be between 100,000-499,999 individuals (BirdLife International, 2020). The only known threat to this species appears to be habitat loss and degradation resulting from deforestation for agricultural and mining activities (Freeman et al., 2018).
Yellow-bearded Greenbul has previously been considered Vulnerable under criteria A2c + 3c + 4c. However, recent data regarding the rate of forest loss may mean that this is no longer tenable and the species may warrant a change in Red List status. Yellow-bearded Greenbul has therefore been reassessed here against all the criteria.
Criterion A: IUCN guidelines stipulate that rates of decline should be measured over the longer of 10 years or 3 generations (IUCN Standards and Petitions Committee, 2019). The generation length for Yellow-bearded Greenbul has been recalculated to 3.1 years (Bird et al., 2020*). Therefore, the rates of reduction for this species are calculated over 10 years.
The population trend for this species has not been directly estimated. However, the only known threat for this species is habitat loss and degradation. Between 2000-2018, there was an 18% reduction in tree cover across this species’ range (Global Forest Watch, 2020). Interpreting the effects of this on population reduction is challenging. This species seems to prefer denser, more mature canopy, and it is not certain that it can exist in degraded habitat. Assuming that the population size declines at the same rate as habitat loss, this equates to a 10% reduction over the last 10 years. Additionally, Tracewski et al. (2016) found negligible levels of deforestation within the range in their analysis. A 10-year reduction rate of 10% is too low to trigger the threatened category (≥30% population size reduction) under this criterion. Yellow-bearded Greenbul may therefore be considered Least Concern under Criterion A.
Criterion B: The Extent of Occurrence (EOO) for this species is too high to trigger the threatened threshold (EOO <20,000 km²) (Birdlife International, 2020). Yellow-bearded Greenbul may be considered Least Concern under Criterion B1. The AOO has not been calculated according to IUCN guidelines (IUCN Standards and Petitions Committee), and so this species cannot be assessed against criterion B2.
Criterion C: The total population is estimated to be between 100,000 and 499,999 total individuals (BirdLife International, 2020), which would equate to roughly 67,000- 334,999 mature individuals. Even assuming that the true population size is at the lower end of this estimate, this is above the threshold (<10,000 mature individuals) to be considered threatened under this criterion. Yellow-bearded Greenbul may therefore be considered Least Concern under Criterion C.
Criterion D: The population size and range are too large to trigger the threshold for listing as threatened under Criterion D; thus Yellow-bearded Greenbul is assessed as Least Concern under this criterion.
Criterion E: To the best of our knowledge, no quantitative analysis has been carried out on this species. Therefore, we cannot assess this species against Criterion E.
We therefore suggest that Yellow-bearded Bulbul (Criniger olivaceus) be listed as Least Concern. We welcome any comments to the proposed listing.
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. By submitting a comment, you confirm that you agree to the Comment Policy.
*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).
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.
Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
BirdLife International (2020) Species factsheet: Criniger olivaceus. Downloaded from http://www.birdlife.org on 07/05/2020
Freeman, B.; Dami, F. D.; Molokwu-Odozi, M> (2018): Status of globally threatened birds of Sapo National Park, Liberia. Ostrich.
Gatter, W. 1997. Birds of Liberia. Pica Press, Robertsbridge, UK.
Global Forest Watch. 2020. World Resources Institute. http://www.globalforestwatch.org (Accessed 06 May 2020).
IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categoreis and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf
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.