40 Introduction: Migration. 



of these white birds, of their fairly swarming at times on other islets, of great 

 flocks literally hanging in clusters on the trees of the little island of Manado 

 tua. So, too, the Nicobar Pigeon, Caloenas, is described as swarming by 

 thousands upon its almost inaccessible breeding islet of Batty Malve in the 

 Xicobars. It is obvious at once that these small islets cannot and do not 

 support such a population of Pigeons for long, consequently the birds are 

 repeatedly on the move, flying over the sea in search of fresh feeding grounds. 

 Instances of their being seen in the act of crossing the sea are given in the 

 text (p. 629, 659). It appears that they visit their breeding islands seasonally, 

 but everything has still to be learnt about the periodicity, if any, of their visits 

 to the other islands of their ranges. The four Pigeons in question have no 

 near affinity with one another; the Nicobar Pigeon is the sole representative of 

 a subfamily ; the other three have more or less near affinities with mainland species. 



As is well known, certain sea-birds, such as the Gannets, Albatroses, and 

 some Terns, resort to particular rocks or other islets to breed. In their case, 

 as in that of the Pigeons, protection of their brood from animals destructive to 

 their eggs and young may well have been the original motive for the adoption 

 of these habits, yet with the Pigeons it remains strange that they avoid the main- 

 land after their young have been safely reared. (For fiuther remarks hereon, 

 ■see pp. 616, 629, 659—661). 



For the sake of the general reader, who may be apt to suppose that narrow 

 straits of the sea offer no barrier to the geographical distribution of trojiical 

 species, it may be mentioned that, so far from this being the case, there is 

 reason to believe that resident species never, or only very exceptionally, cross 

 the sea; were it otherwise the species would not be found with such restricted 

 ranges as is actually the case. 



Migration proper in the East Indian Archipehicjo. — The following is a list 

 of most of the more prominent migratory birds of Celebes. A few species, 

 well known to be migrants, offered difficulties which have led to their being 

 omitted, while a large number of other species have been left out because their 

 migrations are as yet hidden in such obscurity that it would probably be mis- 

 leading to attempt to trace them categorically. In the case of the species given 

 it has often been imjjossible, in the absence of positive data, to avoid speculation 

 in the use of the signs for summer and winter haunts, but it will generally 

 be found that too little has been said, rather than too much. 



O: signifies "summer visitor". (It would generally be safe to assume 

 that the species breeds in the localities so marked, but in not one- 

 half of them have the nest and eggs yet been discovered.) 



X: signifies "winter visitor", or "passes through on migration". 

 + : signifies "rare", or "a straggler". 



