GLACIAL EPOCHS AND POLAR CLIMATES. 53 



tions, and would undoubtedly become entirely so 

 if milder climates again prevailed in North Polar 

 regions. We should then find many species of 

 this group inhabiting an Arctic area, with other 

 species left behind in southern latitudes, just as 

 we find to be the case with the Charadriid/e and 

 the AxATiD.^ at the present time. North Polar 

 condidons are now sufficiently favourable to allow 

 great numbers of Waders and Ducks to visit the 

 Arctic regions, although not sufficiently so for 

 many species of Swallows to visit them, and as a 

 natural consequence the latter birds are still the 

 most abundant in the Southern Hemisphere, whilst 

 the former birds predominate in the Northern 

 Hemisphere. One thing appears to be remarkable 

 about the migration of these Southern Hemisphere 

 species, and that is their comparative shortness. 

 This appears due to the very low southern breeding 

 area. Undoubtedly in the event of the South Polar 

 region once more becoming free from ice, the 

 migratory flights of these birds would be gradually 

 extended south, until they equalled in length those 

 of their Arctic allies. Inversely, we can understand 

 the migrations of Arctic species gradually becoming 

 shorter as glaciation sealed their Polar haunts; 

 culminating probably in a grand emigration of 

 many northern species to Antarctic regions, as we 

 have been endeavouring to demonstrate has actually 

 been the case in past ages. 



In the preceding pages of this chapter I have 

 sought to impress upon the reader the fact that 



