144 THE MIGRATION OF BIRDS, 



now see it, is but a fragment of the vast and regular 

 passage that undoubtedly took place when the 

 Antarctic continent — a region we must remember 

 estimated to be six millions of square miles in 

 extent, or twice the area of Australia — sustained 

 and nourished avian life, and is precisely similar to 

 that migration which took place during the Glacial 

 Epoch in the Northern Hemisphere. Almost the 

 only birds left in this region are those that bred 

 in the lower or temperate zones, and, as in the 

 Northern Hemisphere to-day, these species breeding 

 in the lower zones are remarkable for the com- 

 parative shortness of their migration flights. Not 

 only so, but many of the species now breeding on 

 the outskirts of the glaciated southern continent, 

 either penetrate to the Falkland Islands, Tierra del 

 Fuego, the South Shetlands, and possibly Graham 

 Land, or obtain suitable climatal conditions by 

 vertical migration ; these latter being species that 

 may have lingered in the Southern Hemisphere 

 long after the great Antarctic breeding-grounds had 

 been closed. 



It is a very interesting fact that the now pre- 

 vailing migrations of birds in the Southern Hemi- 

 sphere confirm the views above expressed. If 

 these premises are true, we should not expect to 

 find any extension of migration flight into the 

 Northern Hemisphere during winter in the Southern 

 Hemisphere. Neither do we, save in a few ex- 

 ceptional cases. Let us test the truth of our 

 conclusions by a comparative examination of this 



