54G GEOGRAPHICAL ZOOLOGY. [part iv. 



always to a great extent limited their range. Yet these barriers 

 have not been absolute ; and in the course of ages birds have 

 been able to reach almost every habitable land upon the globe. 

 Hence have arisen some of the most curious and interesting 

 phenomena of distribution ; and many islands, which are entirely 

 destitute of mammalia, or possess a very few species, abound in 

 birds, often of peculiar types and remarkable for some unusual 

 character or habit. Striking examples of such interesting bird- 

 faunas are those of New Zealand, the Sandwich Islands, the 

 Galapagos, the Mascarene Islands, the Moluccas, and the An- 

 tilles ; while even small and remote islets, — such as Juan Fer- 

 nandez and Norfolk Island, have more light thrown upon their 

 past history by means of their birds, than by any other portion 

 of their scanty fauna. 



Another peculiar feature in the distribution of this class is 

 the extraordinary manner in which certain groups and certain 

 external characteristics, have become developed in islands, 

 wliere the smaller and less powerful birds have been pro- 

 tected from the incursions of mammalian enemies, and where 

 rapacious birds — which seem to some degree dependent on the 

 abundance of mammalia — are also scarce. Thus, we have the 

 Pigeons and the Parrots most wonderfully developed in the 

 Australian region, which is pre-eminently insular; and both 

 these groups here acquire conspicuous colours very unusual, or 

 altogether absent, elsewhere. Similar colours (black and red) 

 appear, in the same two groups, in the distant Mascarene islands; 

 while in the Antilles the parrots have often white heads, a 

 character not found in the allied species on the South American 

 continent. Crests, too, are largely developed, in both these 

 groups, in the Australian region only ; and a crested parrot for- 

 merly lived in Mauritius, — a coincidence too much like that of 

 the colours as above noted, to be considered accidental. 



Again, birds exhibit to us a remarkable contrast as regards 

 the oceanic islands of tropical and temperate latitudes; for 

 while most of the former present hardly any cases of specific 

 identity with the birds of adjacent continents, the latter often 

 show hardly any differences. The Galapagos and Madagascar 



