MIGRATION OF BIRDS 11 



4. Australian, embracing Australia, New Guinea, 

 New Zealand and the southern Pacific. 



5. Nearctic, roughly America north of the Gulf 

 of Mexico. 



6. Neotropical, America south of the Gulf. 

 Newton suggested an alteration, a continuous 



northern region to be called the Holarctic Region, 

 which embraces almost the whole of the Northern 

 Hemisphere, and the division of the Australian 

 into Australian and New Zealand Regions. Each 

 of these southern regions is the winter home of some 

 of the Holarctic birds, and it is a matter of dispute 

 whether many of these originated in the northern 

 or southern hemispheres. The value of these 

 artificial divisions of the world is rather in the con- 

 sideration of the conditions their varied climates 

 and physical features present as attractions to birds 

 in search of suitable nesting places and food 

 supplies. 



The study of Migration involves reference to the 

 work of ornithologists of the past and present, the 

 mass of contradictory literature already referred to, 

 and we are repeatedly faced with the difficulty 

 that some particular theory about the vexed 

 questions of the cause or origin of migration, the 

 height and speed at which birds travel, whether 

 they do or do not follow routes, how they find their 

 way, in what order they migrate, how and why 



