|Zosterops erwini (Chasen, 1934)|
Grounds exist for accepting that the previously unrecognised paratypes of Zosterops (palpebrosus) auriventer Hume in Hume & Davison, 1878, from a population inhabiting the coastal lowlands of the Malacca Straits, are all still held by the Natural History Museum, Tring, and that the overall type series is a taxonomic composite. Comparative morphology and a re-reading of original collecting details combine to revise Hume’s identifcation of his paratypes. Their population is re-named and its geographical range redefned, with suggested outcomes for species limits. The term ‘continental’ here includes the islands of South-East Asian shelf waters, i.e., as far the Greater Sundas and their satellites.
Zosterops palpebrosus erwini Chasen, 1934: holotype NHMUK 1947.60.60, adult male (label data), collected by P. M. de Fontaine on Panjang Island (02° 45’N, 108° 54’E), South Natuna archipelago, South China Sea, on 19 August 1931. Described on pages 96–97 of Chasen, F. N. 1934. Nine new races of Natuna birds. Bull. Rafes Mus. 9: 92–97.
Moyle et al. (2009) published genetic evidence of one or more species boundaries between the Indian Subcontinent and Lesser Sundas range extremes of conventionally identifed Z. palpebrosus. One proposal draws on morphology and habitat-based arguments for uncoupling the name auriventer from supposed Oriental White-eyes inhabiting the Malacca Straits and neighbouring coasts, and the consequent retraction of the re-named population’s mainland range southward. This opens a large, terrestrial range gap between inner tropical, mangrove-haunting erwini and williamsoni, and northern, mainly upland forest siamensis. Atention is also drawn to likely habitat-based parapatry between mainly coastal erwini and inland forest buxtoni ‘subspecies’ in eastern Sumatra, and to previously undescribed morphological diferences between erwini and the neighbouring coastal whiteeye population of western mainland Borneo.
These potential taxonomic boundaries all require more data from the feld, particularly on vocalisations, especially song; also sampling for more phylogenetic analysis—to be undertaken before degradation of habitats that could be crucial to understanding fnally eliminates such opportunities. It is proposed that sampling be broad enough to address at least: (1) the level of relatedness of coastal erwini and williamsoni, and of this pair with siamensis, the nearest neighbouring mainland taxon currently accepted as part of true western and northern continental Z. palpebrosus, against the proposition that they are not conspecifc; (2) relatedness of erwini and buxtoni on Sumatra, against the proposition that they are not conspecifc; and (3) status of the coastal Bornean population, relative to both erwini and buxtoni.
D. R. Wells. 2017. Zosterops White-eyes in Continental South-East Asia. 1: Proposed Refinements to the Regional Definition of Oriental White-eye Z. palpebrosus. Bull. B.O.C. 137(2); 100-109.