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A re-evaluation of the species limits in Asian white-eyes Zosterops: implications and an appeal for information to assess the status of the newly-recognised Sangkar White-eye Z. melanurus
Posted on May 23, 2019 by Red List Team (BirdLife International)
The complex of white-eyes that are currently recognised as the species Mountain White-eye Zosterops montanus, Japanese White-eye Z. japonicus, Oriental White-eye Z. palpebrosus, Enggano White-eye Z. salvadorii and Everett’s White-eye Z. everetti (del Hoyo et al. 2016) have been comprehensively reassessed following Wells (2017a, b), Round et al. (2017) and Lim et al. (2019). Three new taxa have been recognised.
Hume’s White-eye Zosterops auriventer Hume 1878, split from Oriental White-eye along with the parts of Everett’s White-eye away from the Philippines; wetmorei and tahanensis, plus medius (previously included within tahanensis) is elevated to subspecies. Range: central Tenasserim, SE Myanmar, South-central Thailand and south through the Thai-Malay Peninsular and S Myanmar (Tenasserim), and Borneo, (Sabah and locally in C, E and S Kalimantan) (del Hoyo et al. 2016, Wells 2017b).
Sangkar White-eye Zosterops melanurus, split from Z. palpebrosus, with subspecies melanurus and buxtoni, but with Sumatran populations of buxtoni tentatively accepted as being a previously misidentified population of Z. auriventer tahanensis, per Lim et al. (2019). Range: Java and Bali.
Swinhoe’s White-eye Zosterops simplex, with subspecies simplex, hainanus, erwini (previously part of Z. p. auriventer), williamsoni from Z. palpebrosus, and the previously recognised Enggano White-eye Zosterops salvadorii, now lumped. Range: breeding E China, from Gansu east of Jiangsu, south to Taiwan (China), Hainan, northeast Vietnam, north Laos and northeast Myanmar (present year-round in the southern half of this area) and non-breeding south to Thailand and central Indochina, plus also resident in the Sundaic region (S. Myanmar, S. Thailand from Ranong and Surat Thani, also Ko Samui, peninsular Malaysia, lowland Sumatra and western lowland Borneo) and around the Gulf of Thailand (from Cambodia and south in Thailand to Pattani at least).
One additional taxon has been lumped.
Japanese White-eye Zosterops japonicus is lumped into Mountain White-eye Z. japonicus, with the subspecies japonicus, insularis, loochooensis, diatoensis, stejnegeri, alani, montanus, whiteheadi, halconensis, parkesi, pectoralis, diuatiae, volcani (note spelling change), difficilis and obstinatus.
Further subspecies rearrangement has taken place.
Ashy-bellied White-eye Zosterops citrinella now includes unicus, previously included within Z. palpebrosus.
Following the re-allocation of the subspecies as outlined above, Oriental White-eye is renamed Indian White-eye Zosterops palpebrosus, with subspecies palpebrosus, nilgiriensis, salimalii, egregious, siamensis and nicobarius. New range: SE Arabia, S Iran, NE Afghanistan, Pakistan and India (including Laccadive Is.), Sri Lanka, Andaman and Nicobar Islands (except S), Nepal, and Bhutan, Myanmar (except far SE), SW China, N, E and SE Thailand and NW Indochina.
Everett’s White-eye Zosterops everetti is now restricted to the Philippines and Talaud Islands, Indonesia with the subspecies boholensis, everetti, siquijorensis, basilicanus, mandibularis and babelo.
Most of these newly-defined taxa are unlikely to be listed as threatened on the Red List. However, the status of the newly recognised Sangkar White-eye is suggested to be of considerable concern due to the incredible volume of trade in the species (Eaton et al. 2015, Lim et al. 2019). A brief outline of the assessment for all newly-defined taxa is given below, followed by a full assessment against each criterion for Sangkar White-eye.
Swinhoe’s White-eye Zosterops simplex
The new range of this species as constituted far exceeds the range thresholds for listing as threatened under Criterion B and it is also considered to have a very large population size. It is described as common in most of the range, indeed the most common bird in secondary forest on Hong Kong, but it is also the most popular cagebird in China (van Balen 2019). It is abundant on Taiwan. The subspecies Z. s. williamsoni is considered common around the Gulf of Thailand and Z. s. erwini (the subspecies previously subsumed within Z. palpebrosus auriventer) is common in peninsular Malaysia, but scarce in Malaysian Borneo and Brunei. On Sumatra the species was common, but there are concerns that the very high numbers of individuals trapped may be impacting the population. Subspecies Z. s. salvadorii is abundant in wooded areas on Enggano (Eaton et al. 2016). As such, the species does not qualify for listing as threatened under Criteria B, C or D. No quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against Criterion E. Despite very high levels of trapping in parts of the species’s range, it remains abundant in many places. While an overall slow decline may be inferred, it is not believed to approach the thresholds for listing as threatened under Criterion A (at least a 30% decline in 10 years, as in this species three generations is less than 10 years [BirdLife International in prep.]). Consequently, Swinhoe’s White-eye is assessed as Least Concern.
Indian White-eye Zosterops palpebrosus
The newly constituted Z. palpebrosus has a very large range and is assumed to have a very large population size, hence is considered Least Concern.
Hume’s White-eye Zosterops auriventer
While the status of the new nominate subspecies of this newly-defined taxon is unclear, the taxon is considered locally fairly common in forest habitat (including plantations) in the Thai-Malay Peninsular but scarce in Sabah (Eaton et al. 2016). There has been considerable forest loss within the range of the species, but the rate of this loss is slower in the upper elevations. For species with lowland Sundaic distributions, rates of loss are up to 1.8% annually (e.g. Cinnamon-headed Fruit-dove Treron fulvicollis: 1.67%, Garnet Pitta Erythropitta granatina: 1.58%). Even using this pessimistic rate (with deforestation encroaching to higher elevations), the rate of decline over the relevant 10 year period does not approach the thresholds for listing as threatened, especially given the species’s tolerance of plantation habitats, but is sufficient to infer a continuing decline in the population. Hence, the species is assessed as Least Concern under Criterion A. The range of the new species is very large, and the population size is thought to exceed the thresholds for listing as threatened. It does not therefore approach the thresholds for listing as threatened under criteria B, C, or D, and Hume’s White-eye is assessed as Least Concern.
Mountain White-eye Zosterops japonicus
This taxon now includes the Japanese White-eye (current BirdLife factsheet), currently listed as Least Concern, and was previously also itself assessed as Least Concern (current BirdLife factsheet). The reconfiguration of the species has not altered the assessment that the species has an extremely large range and is not believed to approach the thresholds for listing as threatened under any of the criteria. Mountain White-eye, as now recognised, is assessed as Least Concern.
Ashy-bellied White-eye Zosterops citrinella
This taxon (BirdLife species factsheet) has seen the addition of the subspecies unicus, which adds the islands of Sumbawa and Flores to the range. Already considered Least Concern, this increases both the range and the global population size of the species, hence Ashy-bellied White-eye continues to be assessed as Least Concern.
Everett’s White-eye Zosterops everetti
This newly defined taxon (BirdLife species factsheet) is present in the southern Philippine Islands, including the Sulu Archipelago and on Talaud. It is common throughout its restricted range (Kennedy et al. 2000), and does not approach the thresholds for listing as threatened under Criterion B. Equally, the population is not believed to approach the thresholds for listing under Criteria C or D. Rates of forest loss have greatly slowed in the Philippines. Taking into account this species’s tolerance of plantation and degraded forest, over the past 10 years the rate of decline is not believed to approach the thresholds for listing as threatened under Criterion A. No quantitative assessment of the species’s risk of extinction has been undertaken, so the species cannot be assessed under criterion E. Consequently, Everett’s White-eye is assessed as Least Concern.
Sangkar White-eye Zosterops melanurus