This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines.
Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.
The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.
Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.
The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.
Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.
Orange-spotted Bulbul (Pycnonotus bimaculatus) is being split into P. bimaculatus and P. snouckaerti, following the application of criteria set out by Tobias et al. (2010).
Prior to the taxonomic change, Pycnonotus bimaculatus (BirdLife species factsheet) was listed as Least Concern, on the basis that it did not approach the thresholds for listing as Vulnerable under any criteria. The population was considered to be stable.
Pycnonotus snouckaerti is restricted to the northern parts of Aceh province, north Sumatra. It is found above 1,000 m and prefers small, scrubby clearings dominated by grass and fern in forested areas and has been described as uncommon (Eaton and Collar 2015, Fishpool and Tobias 2016). Trapping for the bird trade is ongoing in this region and is suspected to have reduced bird populations at sites holding this species (Eaton and Collar 2015). The fact that none were recorded out of over 1,000 P. bimaculatus observed at Sumatran bird markets between 1997 – 2001 (Shepherd et al. 2004) may actually reflect on how restricted the range of the species actually is in comparison with P. bimaculatus and hence the low numbers available, rather than the absence of a threat from trade (Eaton and Collar 2015). However, there seems little evidence upon which to base an estimate of population decline as caused by trade.
The population size is tentatively estimated placed in the band of 2,500-9,999 mature individuals based on an assessment of known records, descriptions of abundance and range size. This is consistent with recorded population density estimates for congeners or close relatives with a similar body size, and the fact that only a proportion of the estimated Extent of Occurrence is likely to be occupied. On the assumption that the species is undergoing an ongoing population decline due to an unquantified threat from trade, coupled with a degree of habitat conversion and degradation, it is proposed to list the species as Vulnerable under category C2a(ii).
Pycnonotus bimaculatus (as defined following the taxonomic change) occurs in higher altitude forest (above 800 m) on Bali, Java and south, central and part of northern Sumatra (Eaton and Collar 2015). 1,322 were reported from regular monitoring of the markets in Medan during 1997-2001 (though this includes an unknown proportion of birds counted multiple times) (Shepherd et al. 2004, Shepherd 2006), and Harris et al. (2015) reported the trade volume per year to be 240 prior to 1989 and 270 per year for 2013-14. An expert consultation for that study considered the species to be ‘Declining’ in Sumatra, rather than ‘Severely Declining’ (Harris et al. 2015).
Due to the unknown effect of trapping, it is very difficult to make population size estimates for the species. As the entire range of the species occurs within a region subject to high trapping pressure where this species is targeted, a precautionary proposal is made to list P. bimaculatus as Near Threatened on the basis of a suspected population decline that approaches the threshold for Vulnerable (a 30-49% population decline within the past, current or future three generation period).
Comments and extra information that might allow for better population size and trend estimates are sought.
Eaton, J.A. and Collar, N.J. 2015. The taxonomic status of Pycnonotus bimaculatus snouckaerti. Forktail 31: 107-110.
Fishpool, L. & Tobias, J. (2016). Orange-spotted Bulbul (Pycnonotus bimaculatus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/57950 on 31 August 2016).
Shepherd, C. R., Sukumaran, J. & Wich, S. A. 2004. Open season: an analysis of the pet trade in Medan, Sumatra. Selangor: TRAFFIC Southeast Asia.