CHAP. XVIII.] 



BIRDS. 



331 



African Psittacus, have been found. But the origin of so wide- 

 spread, isolated, and. varied a group, must be far earlier than 

 this, and not improbably dates back beyond the dawn of the 

 Tertiary period. Some primeval forms may have entered the 

 Australian region with the Marsupials, or not long after them ; 

 while perhaps at a somewhat later epoch they were introduced 

 into South America. In these two regions they have greatly 

 nourished, while in the two other tropical regions only a few 

 types have been found, capable of maintaining themselves, among 

 the higher forms of mammalia, and in competition with a more 

 varied series of birds. This seems much more probable than 

 the supposition that so highly organized a group should have 

 originated in the Australian region, and subsequently become 

 so widely spread over the globe. 



Order IV.COLUMB^. 



FAMILY 84 COLUMBIDJE. (44 Genera, 355 Species.) 

 GENERAL DISTRIBUTION. 



The Columbidae, or Pigeons and Doves, are almost universally 

 distributed, but very unequally in the different regions. Being 

 best adapted to live in warm or temperate climates, they dimin- 

 ish rapidly northwards, reaching about 62 N. Latitude in North 

 America, but considerably farther in Europe. Both the Nearc- 

 tic and Palsearctic regions are very poor in genera and species 

 of pigeons, those of the former region being mostly allied to 

 Neotropical, and those of the latter to Oriental and Ethiopian 

 types. The Ethiopian region is, however, itself very poor, and 

 several of its peculiar forms are confined to the Madagascar sub- 

 region. The Neotropical region is very rich in peculiar genera, 

 though but moderately so in number of species. The Oriental 



