Ardea
Official journal of the Netherlands Ornithologists' Union

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Mees G.F. (1951) Het areaal van Zosterops palpebrosa buxtoni Nicholson op Java. ARDEA 39 (1-3): 196-218
In this paper the geographical distribution of Zosterops palpebrosa buxtoni Nich. on Java is discussed. Its occurrence is much more restricted than indicated in most publications, the race being found only in the residencies of Bantam and Buitenzorg, as shown on map I. Much attention, is paid to the differences between this grey-bellied race and the yellow-bellied Zosterops palpebrosa gallio Sharpe; the latter being distributed over the whole of Java except Bantam, whereas the populations in the central part of the residency of Buitenzorg are of intermediate character. Apart from having a yellow belly, gallio differs in being of slightly larger size, which is shown in graph 1. The peculiar distribution of Z. p. buxtoni indicates that it may be an immigrant from southern Sumatra, a possibility that is strongly corroborated by the fact that the Sumatran birds, known under the name Z. palpebrosa sumatrana Kloss, proved to be inseparable from Z. p. buxtoni (apart from other material, 4 from the 7 specimens of Kloss' 'type-series' were available for comparison). In colour variation as well as in size they fall completely within the variation range of buxtoni; as regards the size of the wing this is shown in graph II. Therefore the race sumatrana must be considered a synonym of buxtoni, inhabiting the whole of Sumatra and parts of the residencies Bantam and Buitenzorg in westernmost West-Java. As the form buxtoni, immigrating from Sumatra in NW.-Bantam, would not have been able to maintain its grey belly, if at that time Bantam was inhabited already by gallio (the two races interbreeding freely), it seems likely that at the time of immigration, this part of West-Java was not yet occupied by any race of the species Zosterops palpebrosa, and that afterwards the forms buxtoni, advancing from the West, and gallio, advancing from the East, met in the residency of Buitenzorg. Supporting evidence is given that this occupation must have taken place rather recently. The vertical distribution of Z. p. buxtoni, and the possibility of its being influenced by the presence of competing Zosterops-species are discussed. Stresemann (1939) most probably was not correct in assuming that competition plays an important role; it seems much more likely that the species limits itself by habitat preference. Attention is paid to the hereditary of the yellow belly in gallio. As the hybrid populations show all kinds of intergradations between yellow and grey, Stresemann's view (1931) that the yellow coloration depends on one single genetic factor only, seems in this case not quite correct. The conclusions are based upon a material of 214 skins, drawn from the collections in the Amsterdam Museum, the Leiden Museum, the Buitenzorg Museum, coll. Bartels and coll. Van Heurn.


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