Archived 2020 topic: Grey-cheeked Bulbul (Alophoixus tephrogenys): revise global status?

BirdLife species factsheet for Grey-cheeked Bulbul

The Grey-cheeked Bulbul (Alophoixus tephrogenys) is a songbird species resident throughout the Sundaland region of Southeast Asia; including Brunei, both Peninsular and Borneo’s East Malaysia, central to eastern Sumatra (Indonesia), and southern parts of Myanmar and Thailand (del Hoyo et al. 2020; eBird 2020). Until recently, the species was considered conspecific with the Brown-cheeked Bulbul (A. bres) and the Palawan Bulbul (A. frater). The Grey-cheeked Bulbul prefers mature broadleaf forests, as well as tidal swamps or mixed deciduous forests, but can also tolerate logged forests and overgrown plantations (including cocoa and oil-palm plantations) (del Hoyo et al. 2020).

The species was previously not thought to be at immediate risk from deforestation or habitat loss due to its tolerance to such conditions (del Hoyo et al. 2020). A study on market data surrounding the wild bird trade had also found that the conspecific species A. bres had seen stable to increasing population trends throughout much of the 2000’s (Harris et al. 2015). A recent forest analysis of the Sundaland region however suggests that the Grey-cheeked Bulbul may be increasingly threatened by habitat loss (Symes et al. 2018). Owed to a number of factors such as logging, land conversion for industrial plantations, and forest fires, the Sundaic lowlands had experienced a loss of over 70% of its original forest cover by 2010 alone. The intensive trade for birds further compounds forest destruction and habitat loss, with the Grey-cheeked Bulbul facing significant pressures in trapping for domestic and international markets (Symes et al. 2018). The population size of the species was previously unknown. However, using population density estimates of 10-14.5 individuals/km2 (del Hoyo et al. 2020), and precautionarily assuming that only 10% of the total mapped range (c. 874,155 km2) is occupied, the population may number 874,160-1,267,532 individuals. This roughly equates to 582,773-845,021 mature individuals, rounded here to 580,000-850,000 mature individuals. To account for uncertainty, the population size is placed tentatively in the band of 500,000-999,999 mature individuals.

The Grey-cheeked Bulbul is currently listed as Least Concern as the species was not considered to approach any relevant threshold for a threatened status. However, new information regarding hunting and forest loss data may warrant a change in Red List status. Therefore, the species will be re-assessed against all criteria:

Criterion A – Following recent findings, the generation length of the Grey-cheeked Bulbul is assessed as 2.8 years (Bird et al. 2020)*. Under IUCN guidelines (IUCN Standards and Petitions Committee, 2019), the relevant timeframe for an assessment against Criterion A is the longer of a three-generation period or ten years; hence population declines of this species have to be quantified over ten years.

The Grey-cheeked Bulbul is thought to be undergoing population declines due to habitat loss and trapping and hunting for trade. A recent study investigating both factors across the Sundaic region found that the range has been lost a rate of 17.3% over ten years (Symes et al. 2018; see also Tracewski et al. 2016). However, due to the tolerability of the species to forest loss, habitat loss alone may not cause rapid population declines. Due to the pressure of hunting however, the species is thought to be undergoing additional declines of 56.5% over the same period; overall accounting for a 73.8% decline over an estimated ten-year period (Symes et al. 2018). Due to the ongoing threats caused by habitat loss and hunting, we can assume that population declines are likely to continue into the future. Thus, the species qualifies for Endangered under Criterion A2cd+3cd+4cd.

Criterion B – The Extent of Occurrence (EOO) for this species is estimated at 3,310,000 km2. This is outside the required threshold for a threatened status under Criterion B1. Therefore, the species qualifies for Least Concern under Criterion B1. The Area of Occupancy (AOO) was not quantified for this species as required (IUCN Standards and Petitions Committee, 2019); thus, the species cannot be assessed against Criterion B2.

Criterion C – The estimated population size of this species (500,000-999,999 mature individuals) is outside the required thresholds for a threatened status under this criterion. Therefore, the species qualifies for Least Concern under Criterion C.

Criterion D – The estimate population size and range of this species does not approach any relevant threshold for a threatened status under this criterion. Therefore, the species qualifies for Least Concern under Criterion D.

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.

Therefore, it is suggested that the Grey-cheeked Bulbul (Alophoixus tephrogenys) be reclassified as Endangered A2cd+A3cd+A4cd. We additionally ask for information on the timeframe of the genuine decline of the species: 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 its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. 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.

References

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.

del Hoyo, J., Fishpool, L., Collar, N., Tobias, J., and Kirwan, G. M. (2020). Grey-cheeked Bulbul (Alophoixus bres), version 1.0. In Birds of the World (S. M. Billerman, B. K. Keeney, P. G. Rodewald, and T. S. Schulenberg, Editors). Cornell Lab or Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.gycbul1.01

eBird. 2020. eBird: An online database of bird distribution and abundance. Ithaca, NY, USA Available at: http://www.ebird.org. Accessed 26th May.

Harris, J. B. C., Green, J. M. H., Prawiradilaga, D. M., Giam, X., Giyanto, Hikmatullah, D., Putra, C. A., and Wilcove, D. S. (2015). Using market data and expert opinion to identify overexploited species in the wild bird trade. Biological Conservation; 187, 51-60.

IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf

Symes, W. S., Edwards, D. P., Miettinen, J., Rheindt, F. E., and Carrasco, L. R. (2018). Combined impacts of deforestation and wildlife trade on tropical biodiversity are severely underestimated. Nature Communications 9: 4052.

Tracewski, Ł., Butchart, S. H. M., Di Marco, M., Ficetola, G. F., Rondinini, C., Symes, A., Wheatley, H., Beresford, A. E., and 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.

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3 Responses to Archived 2020 topic: Grey-cheeked Bulbul (Alophoixus tephrogenys): revise global status?

  1. Red List Team (BirdLife International) says:

    The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you,
    BirdLife Red List Team

  2. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list the Grey-cheeked Bulbul as Vulnerable under Criterion A2cd+3cd+4cd.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021 (information on the IUCN Red List update process can be found here), following further checking of information relevant to the assessments by both BirdLife and IUCN.

  3. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Grey-cheeked Bulbul is recommended to be listed as Vulnerable under Criterion A2cd+3cd+4cd.

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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