INTERNAL MIGRATIONS. 141 



same. Probably much of it was initiated in equa- 

 torial regions during periods of intense local glaci- 

 ation ; whilst many of these mountain migrants in 

 more temperate zones may be the last survivors of 

 the hosts of birds that were driven from Polar zones 

 by the Post-Pliocene Glacial Epoch ; remaining 

 behind to breed in regions that were once on the 

 immediate margin of the glaciers, and in their 

 movements at the present day very clearly indi- 

 cating the nature and extent of that migration that 

 prevailed during the acute phases of Polar glaciation 

 in past ages. Whilst other species, even other 

 individuals, have gradually extended their northern 

 flights towards that olden Polar Paradise, these have 

 remained content with shorter pilgrimages; although, 

 in every instance, it will have been remarked that 

 the object attained (a similarity of breeding tempera- 

 ture) is precisely the same. 



We now pass to the migration of birds in the 

 Southern Hemisphere. Unfortunately we have 

 many obstacles to contend with, and are placed at 

 considerable disadvantage in our study of bird 

 migration in this region. In the first place, the 

 data on which any conclusions may be based are 

 somewhat meagre, partly owing to the scarcity of 

 any careful and intelligent observation, and partly 

 owing to geographical peculiarities, rendering 

 migratory movements not only few but exceedingly 

 restricted, in comparison with the vast flights of 

 northern species. Nevertheless migration in the 

 Southern Hemisphere, as I hope ultimately to show, 



