Ardea
Official journal of the Netherlands Ornithologists' Union

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Hoogerwerf A. (1967) Verspreiding en voedsel van Caloenas nicobarica en Ducula bicolor. ARDEA 55 (3-4): 249-259
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On account of a previous paper on the subject (Bartels 1964) the present author thinks it useful to publish his experiences obtained in Indonesia, including West New Guinea, with both the Nicobar Pigeon, Caloenas nicobarica, and the Pied Imperial Pigeon, Ducula bicolor. Without having a detailed knowledge about the reasons for the wandering habits of these fruit consuming pigeons and the distances covered, the available information makes it almost certain that indeed wandering takes place. Evidence is brought forward that the two species certainly do not always occur together, nor that Sterculia foetida, a tree frequently found on coral islands, need to be spread by Ducula bicolor, as seems to have been suggested by Bartels. From the accompanying list of crop- and gizzard contents of about 100 specimens belonging to 12 different species of birds, mainly pigeons, it is evident that also the Island Imperial Pigeon (Ducula rosacea), as well as the Koel (Euedynamys scolopacea) and the Large-billed Crow (Corvus macrorhynchos) consume Sterculia-fruits; all these three species are often found in the same areas with Caloenas nicobarica. Though an endozoic seed-distribution of Sterculia foetida in the islands of the Bay of Djakarta by birds is not excluded, the present author thinks it more probable that the growth of this very useful tree was in the first place stimulated by man. As to the stones often found in the stomach of the Nicobar Pigeon, the author is of the opinion that in all cases where he observed the species, the origin of such stones did not present a puzzle. As next to nothing is known about the extent of the wanderings of the Nicobar Pigeon, more particulars are necessary before the occurrence of these digestive attributes may be put down to something mysterious. Though it seems right to regard small islands as the favourite habitat of the Nicobar Pigeon, the species is also known from larger islands and from the 'Tafelberg' forest reserve near Manokwari which is on the mainland of New Guinea. Stomach- and crop contents of Ducula bicolor show that this pigeon does not exclusively live on berries and soft fruits, as was thought by Bartels. Birds of this species were repeatedly observed feeding on fruits of the Corypha utan palm, which, like the fruits of Sterculia foetida, cannot be called soft fruits. The statement that the 'Nicobar Pigeon is strictly a terrestrial bird' is disputed, as these birds, when frightened, use to disappear in trees, often looking for cover in the foliage of the summits of forest giants where they may remain for a considerable time. In addition it nests in shrubs and trees. From the particulars given in the list of stomach- and crop contents it is demonstrated how prominent the part of fruitpigeons and other fruit consuming birds may be in the distribution of forest trees. Species of rather small size appear to consume much larger fruits than one should expect.


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