Pale-bellied Myna (Acridotheres cinereus): revise global status?

BirdLife species factsheet for Pale-bellied Myna

The native range of Pale-bellied Myna (Acridotheres cinereus) is restricted to South Sulawesi, north to Rantepao (Coates and Bishop 1997, del Hoyo and Collar 2016). There are also small, but apparently increasing, populations in Sarawak (Gregory-Smith 1997) and Sabah (Malaysia) (Wong Tsu Shi 2009, Myers 2009), and West Kalimantan (van Balen et al. 2013), Borneo. There does not appear to be evidence for this species having been introduced to Sumba and Flores, where records of introduced Javan Myna (A. javanicus) may have been attributed to this species. Confusion over the species boundaries, and the native ranges, within Acridotheres has masked the true conservation status of the species involved.

Divining the conservation status continues to prove problematic however. Large numbers of Acridotheres mynas, including the present species, Javan Myna and Great Myna (A. grandis) are traded in bird markets throughout Asia. An unknown fraction of each species are trapped from the wild, but many are also being reared in captivity, with the true picture of the wild status of these species now becoming clouded by escapes and introductions. In addition, there may be deliberate or accidental hybridisation in captivity, and potentially hybridisation may occur in recently founded populations, as suspected in Borneo (Wong Tsu Shi 2018). Within the native range, Javan Myna (BirdLife factsheet) is listed as Vulnerable due to the suspected rapid rate of population decline due to the volume of trade.

Pale-bellied Myna has a relatively small native range and there is concern that this species has also been heavily trapped to supply the cagebird trade within Indonesia. Concern that the species may have disappeared from large parts of its range already suggests that the species is of greater conservation concern than the current assessment as ‘Least Concern’ (BirdLife International 2019). Therefore, the species is being reassessed here against all criteria.

Criterion A – The population trend for this species has not been directly estimated. However, trapping is believed to have led to this species becoming far more difficult to find in recent years, although there are still regular sightings of small groups. As the species was previously lumped with A. javanicus and sometimes also A. grandis, it received little attention, and has even been treated as an introduced population of A. javanicus (e.g. Strange 2001). The historical assessment of the abundance runs to two statements; White and Bruce (1986) suggest it is common to 1000 m, and Holmes (1996) moderate this to ‘quite common’. We can certainly infer that there has been a moderate to rapid decline since then, as it appears to be rare and highly localised now. For A. javanicus, it was necessary to infer the rate of decline from numbers in trade. Unfortunately, unlike Javan Myna, there is very little information upon which to base this inference: Pale-bellied Myna is not reported in the inventories detailing large volumes of trade in Acridotheres in Indonesia (e.g. Shepherd 2006, Chng et al. 2015, Rentschlar et al. 2018). A decline can be suspected, but there is no direct evidence recorded from markets for this species to allow an assessment of the rate of decline. Therefore it is not possible to assess the species under Criterion A without additional information.

Criterion B – The Extent of Occurrence (EOO), based on a minimum convex polygon around previous occurrence locations for this species is 25,400 km2. The Area of Occupancy (AOO) has not been calculated. The EOO exceeds the threshold for listing the species as threatened under Criterion B1. However, this figure is now likely to be out of date given the apparent reduction in occurrence across the former range. There are still recent records from around Makassar and towards the northern edge of the native range however, so the reduction in EOO will not be dramatic: the extinction risk is still spread across a large area. On this basis, the range of the species may be considered to approach the thresholds for listing as Vulnerable under B1, and therefore be eligible for listing as Near Threatened under this criterion. However, there are two additional conditions to consider to assess if the species merits this listing.  

The species is not known to undergo any extreme fluctuations so it would not trigger condition c). Yet, given the recognised level of trapping occurring within the range of the species we can infer an ongoing decline in at least population size. Thus condition b(v) is met.

For condition a), the species needs to be severely fragmented or to occur at a limited number of locations* (2-5 for Endangered; 6-10 for Vulnerable). The species is unlikely to fulfil the specifications for ‘severely fragmented’ (see IUCN Standards and Petitions Subcommittee 2017), but it does likely occur at a small number of locations. As a location depends on the main threat to a species, the accessibility of the remaining population to trappers is the key parameter. The nature of the threat suggests that the number of locations must be very few, given that the species occurs in lowland agricultural areas. Where located, there appears little to dissuade bird trappers from targeting the species, as this group of closely related myna species is highly popular in the bird markets. While the species may not be explicitly targeted, it is likely to be trapped wherever it is noted. On a precautionary basis, the number of locations is here considered fewer than 10. Further thoughts/comments on the suitability of this number of locations (with reference to the definition below) given information on the behaviour of trappers in South Sulawesi would be useful. Nevertheless, the current Extent of Occurrence of the species is still too large to qualify for listing at a higher threat category under Criterion B1. Therefore overall, Pale-billed Myna warrants listing as Near Threatened, approaching the threshold for listing as threatened under Criterion B1ab(v).

Criterion C – Only the population within the native range, in southern Sulawesi south of Rantepao, can be considered for the Red List assessment, as introduced populations outside of the range do not count towards the current estimate of the wild population. No estimate is available from the literature for the population size of the species, and there are few recent records from which to derive an estimate. Additionally, the threat of trapping renders any density extrapolation to area of suitable habitat implausible. The species is now rare and hard to locate, and is known to have been heavily trapped and traded. An assumption can be made that the population is therefore likely to be relatively small. The species is now infrequently recorded; the largest group observed in recent years appears to be 30 individuals recorded by Ashley Banwell in 2017 near Lompobattang. This suggests that the species occurs at extremely low densities, and it is highly likely that the population size is below 10,000 mature individuals. Unless new information on the population size becomes available, we can assume that the species meets the threshold for listing as Vulnerable under Criterion C (< 10,000 mature individuals). However, to warrant listing under this criterion requires other conditions to be met.

The rate of decline has not been accurately estimated or observed, and it is not known to undergo extreme fluctuations, so the species does not warrant listing as threatened under Criteria C1 or C2b, respectively. However, within the natural range the species now likely forms one single population, and hence qualifies for listing as Vulnerable under Criterion C2a(ii). Any information on the precautionary population estimate derived here are greatly welcome.

Criterion D – The population size is unknown. It is not thought likely that it is below 1,000 mature individuals, hence it is not believed to qualify for listing under Criteria D1. The range is not highly restricted, so it also does not qualify for listing under D2. Overall, the species is thus considered Least Concern under Criterion D.

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

Therefore, if the assumption is accepted that the current population is below 10,000 mature individuals on the basis of the paucity of recent records and concern over the level of trapping, the species warrants listing as Vulnerable under Criterion C2a(ii). However, any estimates of density or relative abundance in the recent past that could be used to support an estimate of the rate of decline, or any additional information on the potential population size would greatly benefit this assessment.

Please note, though, 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 information that is sought, or about the species’ Red List status.

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

References

BirdLife International. 2019. Species factsheet: Acridotheres cinereus. Downloaded from http://www.birdlife.org on 30th April 2019.

Chng, S. C. 2015. In the market for extinction: an inventory of Jakarta’s bird markets. Traffic.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.

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.

Gregory-Smith, R. 1997. Pale-bellied Myna Acridotheres cinereus in Sarawak. Malayan Nature Journal50, 355-357.

Holmes, D. A. (1996). The birds of Sulawesi. Oxford University Press.

Myers, S. 2016. Birds of Borneo. 2nd edition. Christopher Helm, London.

Rentschlar, K. A., Miller, A. E., Lauck, K. S., Rodiansyah, M. 2018. A Silent Morning: The Songbird Trade in Kalimantan, Indonesia. Tropical Conservation Science. https://doi.org/10.1177/1940082917753909

Shepherd, C. R. 2006. The bird trade in Medan, North Sumatra: an overview. Birding Asia, 5, 16-24.

Strange, M. (2001). A photographic guide to the birds of Indonesia. Princeton University Press.

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.

van Balen, S., Trainor, C. and Noske, R. 2013. Around the Archipelago. Kukila 17 (1): 41-72. Wong, Tsu Shi. 2009. Makassar Myna – New Bird for Sabah. Blogpost at ‘Of North Borneo Birds and others’, available at http://borneobirds.blogspot.com/2009/11/jungle-myna-new-bird-for-sabah.html. Accessed 30th April 2019.

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1 Response to Pale-bellied Myna (Acridotheres cinereus): revise global status?

  1. Rob Martin (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2019 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    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 those in the initial proposal.

    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.