Archived 2020 topic: Brown-cheeked Bulbul (Alophoixus bres): Revise global status?

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.

References

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.

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6 Responses to Archived 2020 topic: Brown-cheeked Bulbul (Alophoixus bres): Revise global status?

  1. James Eaton says:

    The species has suffered a catastrophic decline over the past few years – as predicted in Eaton et al 2015 and mentioned in Lee et al 2016, when still lumped with Grey-cheeked Bulbul – which itself has been proposed for Endangered, yet this bird is not common anywhere anymore, especially in comparison to Grey-cheeked, which is still locally numerous in Thailand and Malaysia.

    The species is now becoming exceedingly rare and difficult to find in the field even in protected parks such as Gunung Halimun-Salak National Park and Alas Purwo National Parks, where just five years ago it was still reasonably common. Without urgent action, this species will disappear – it’s following the same steep trajectory as too many other Javan/Bali endemics, and I would certainly recommend Critically Endangered for some urgent action to take place, or at the very least, Endangered.

    Below is our data from two full inventory surveys of Jakarta’s three biggest markets, on the same dates, five years apart.
    Total number of birds recorded on market survey, showing decline of not just numbers encountered, but also as a percentage of total number of birds.
    Brown-cheeked Bulbul:
    July 2019: 13 birds (from a total of 14617) = 0.09% of total
    July 2014: 178 birds (from a total of 19036) =0.94% of total

    As a side interest of other Alophoixus species):
    Grey-cheeked Bulbul:
    July 2019: 5 birds
    July 2014: 34 birds
    Ochraceous Bulbul:
    July 2019: 34
    July 2014: 58

    Bali market survey:
    Brown-cheeked:
    2017: 1
    2018: 3
    Stuart Marsden, Tom Squires and Harry Marshall we be able to provide field data from the ‘Big Month’ citizen science event.

    James

  2. Stuart Marsden says:

    Brown-cheeked Bulbuls have been regularly observed in market surveys in Java and Bali during the last ten years. A 2018 survey of bird ownership involving over 3,000 households in all six of Java’s provinces estimated that 340,620 ± 54,354 individuals of Alophoixus spp are currently kept in Java alone (Marshall et al. 2020). Market surveys in Jakarta and Bali in 2014 and 2019 (J. Eaton unpubl. data) recorded more Brown-cheeked Bulbuls A. bres (195 individuals) than Grey-cheeked Bulbul A. tephrogenys (40) and Ochraceous bulbul A. ochraceus (93) combined, so it is likely that a high proportion of the individuals in Marshall et al.’s (2020) survey were indeed this species.
    During the ‘Big Month’ citizen science event (January 2020; 22,054 checklists) across Java and Bali, Alophoixus bres was recorded in just 8 (0.1%) of the 7,935 tetrads (2 × 2 km squares) visited (T. Squires & S. Marsden in litt. 2020).

    It is our opinion that this species has been undoubtedly in extreme decline across Java both as a result of lowland habitat loss and bird trapping. We also suggest that it is currently very rare and at best patchily distributed. While it is impossible with current data to estimate the extent of the decline, but it is likely that the species has declined by over 50% in the last ten years, and very possible that this decline has been in excess of 80%.

  3. Bas van Balen says:

    The bulbul has disappeared from most former haunts, for instance between 1981 and 1990 I found it common at 35 different localities throughout Java and Bali, and you could find it in most, if not all all forest patches, small to large, secondary to primary. How different with the present situation.

  4. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. 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 once again,
    BirdLife Red List Team

  5. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information on the increased rarity of the species, as well as decline rates that are likely exceeding the required thresholds for higher threatened category, our preliminary proposal for the 2020 Red List would be to list the Brown-cheeked Bulbul as Endangered 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, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  6. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Brown-cheeked Bulbul is recommended to be listed as Endangered 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.

Comments are closed.