CHAP. XVIII.] BIRDS. 335 



Zealand, Tristan d'Acunha, and other oceanic islands ; and the 

 phenomenon is clearly dependent on the long-continued absence 

 of enemies, which allowed of great increase of bulk and the 

 total loss of the power of flight, without injury. In some few 

 cases (the Ostrich for example) birds incapable of flight co-exist 

 with large carnivorous mammalia ; but these birds are large and 

 powerful, as well as very swift, and are thus able to escape from 

 some enemies and defend themselves against others. The entire 

 absence of the smaller and more defenceless ground-birds from 

 the adjacent island of Madagascar, is quite in accordance with 

 this view, because that island has several small but destructive 

 carnivorous animals. 



General Remarks on the Distribution of the Golumhce. 



The striking preponderance of Pigeons, both as to genera and 

 species, in the Australian region, would seem to indicate that at 

 some former period it possessed a more extensive land area in 

 which this form of bird-life took its rise. But there are other 

 considerations which throw doubt upon this view. The western 

 half of the Malay Archipelago, belonging to the Oriental region, 

 is also rich in pigeons, since it has 43 species belonging to 11 

 genera, rather more than are found in all the rest of the Oriental 

 region. Again, we find that the Mascarene Islands and the An- 

 tilles both possess more pigeons than we should expect, in pro- 

 portion to those of the regions to which they belong, and 

 to their total amount of bird-life. This looks as if islands were 

 more favoui-able to pigeon-development than continents ; and if 

 we group together the Pacific and the Malayan Islands, the 

 Mascarene group and the Antilles, we find that they contain to- 

 gether about 170 species of pigeons belonging to 24 out of the 47 

 genera here adopted ; while all the great continents united only 

 produce about the same number of species belonging (if we omit 

 those peculiar to Australia) to only 20 genera. The great deve- 

 lopment of the group in the Australian region may, therefore, be 

 due to its consisting mainly of islands, and not to the order 

 having originated there, and thus having had a longer period in 

 which to develop. I have elsewhere suggested (Ibis 1865, p. 366) 



