Bartels E. (1964) Vragen rond het merkwaardige leven van de Manenduif Caloenas nicobarica (L.). ARDEA 52 (1-2): 93-98

The Nicobar Pigeon Caloenas nicobarica occurs on small, wooded coral islands of the Indo-Australian archipelago and the south-western part of the Pacific Ocean. The author reports the frequent occurrence of a relatively large, often beautifully coloured, hard semi-precious stone in the stomach of these birds. Section on 12 birds collected by Bartels on small islands in the Bay of Batavia between 1912 and 1928 revealed that nine birds carried one such stone in the stomach; one had no stone, whereas about two specimens there is no record. The food remains in the stomachs consisted of hard fruits with seeds, and/or hard fruit-stones. The question is raised as to where these birds may have found their stomach-stone, which, incidentally, is treasured by the natives (Java; Malaya, cf. Wolfe 1951), as siliceous stones just do not occur on coral islands. Further there is the question about the identity of the exceptionally hard fruits and fruit-stones which are being crushed by the powerful gizzard aided by the siliceous 'rubstone' inside. The author points out that the wide range of the Nicobar Pigeon virtually coincides with that of the Pied Imperial Pigeon Ducula bicolor, and that of the Kalumpang tree (Sterculia foetida). The Nicobar Pigeon is strictly a terrestrial bird, walking on the forest ground in search of fallen seeds and fruits, contrary to the habits of the Pied Imperial Pigeon, which is a typical bird of the tree tops, where it lives on berries and soft fruits.