BirdLife International factsheet for Brown-cheeked Bulbul.
The Brown-cheeked Bulbul (Alophoixus bres) is endemic to the Indonesian islands of Java and Bali, where it inhabits moist lowland and montane forests (BirdLife International, 2020). Alophoixus bres was taxonomically split in 2016 (BirdLife International, 2020). Prior to the split, the species was described as common to very common (del Hoyo et al., 2005), but the global population size for the post-split species has not been quantified. Brown-cheeked Bulbul is highly threatened by the domestic songbird trade (Symes et al., 2018), and this exploitation is suspected to be causing large population declines.
Previously, Brown-cheeked Bulbul has been considered Near Threatened, approaching threatened status under Criterion A2d+3d+4d. However, new information regarding population trends may mean that the current Red List category is no longer tenable. We have therefore reviewed this species here against all Red List criteria:
Criterion A: The population trend of Brown-cheeked Bulbul has not been directly estimated, but its vulnerability to the songbird trade is believed to be causing significant population declines. 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 Brown-cheeked Bulbul has been recalculated to 2.8 years (Bird et al., 2020)*. Therefore, the rates of decline for these species are calculated over the length of 10 years.
While the rate of decline has not been quantified directly, Symes et al. (2018) suggest that it could be as high as 98% over 10 years due to the combined impacts of hunting and habitat loss. Furthermore, during the ‘Big Month’ citizen science event that took place across Java and Bali in January 2020, Brown-cheeked Bulbul was recorded in only 8 of the 7,935 surveyed 4km² tetrads (Squires & Marsden in litt., 2020). This reporting rate of 0.1% suggests that the species is now increasingly rare throughout its range.
There remains uncertainty about exact decline rates, and more detailed information is still required. In the meantime, as further evidence suggests this species is undergoing rapid declines, the rate of decline is suspected to be >30%, precautionarily placed here in the 30-49% band. As such, Brown-cheeked Bulbul may be considered Vulnerable under Criterion A2cd+3cd+4cd.
Criterion B: The Extent of Occurrence for this species is too big to trigger the threatened threshold (EOO <20,000 km²) under Criterion B1. Brown-cheeked Bulbul may therefore be considered Least Concern under this criterion. The Area of Occupancy has not been quantified according to IUCN guidelines (see IUCN Standards and Petitions Committee, 2019), and the species cannot be assessed against Criterion B2.
Criterion C: The population size for this species has not been estimated, and thus it cannot be assessed against this criterion. Given the suspected rapid declines, we seek recent information on the population size and subpopulation structure to comprehensively assess the species against Criterion C.
Criterion D: The population size for this species has not been estimated, and thus it cannot be assessed against this criterion. Given the suspected rapid declines, we seek recent information on the population size.
Criterion E: To the best of our knowledge, no quantitative analysis has been carried out for this species, so it cannot be assessed against this criterion.
We therefore suggest that Brown-cheeked Bulbul (Alophoixus bres) be listed as Vulnerable under Criterion A2cd+3cd+4cd. We specifically ask for recent information on the population size and subpopulation structure. We additionally ask for information on the timeframe of declines: Data from Symes et al. (2018) suggests that declines accelerated between 2000 and 2015, meaning that the species may have crossed the threshold for listing as Vulnerable during 2008-2012 or during 2012-2016. We welcome any comments to the proposed listing and suggested timing of change.
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., Şekercioğlu, Ç.H. and 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: Alophoixus bres. Downloaded from http://www.birdlife.org on 26/05/2020.
del Hoyo, J.; Elliott, A.; Christie, D. 2005. Handbook of the Birds of the World, vol. 10: Cuckoo-shrikes to Thrushes. Lynx Edicions, Barcelona, Spain.
IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categories and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf
Symes, W. S., Edwards, D. P., Miettinen, J., Rheindt, F. E., & Carrasco, L. R. 2018. Combined impacts of deforestation and wildlife trade on tropical biodiversity are severely underestimated. Nature communications 9(1): 4052.