DESTINATIONS OF THE MIGRANTS. 189 



half of that zone. As a natural consequence, 

 double the number of species retreated south 

 into Europe and Asia, than penetrated into North 

 America; or if the numbers were about equal, 

 competition between species being keener, owing 

 to more restricted area, and climate being so much 

 more unfavourable to avian life, a much higher 

 rate of mortahty resulted in a present avifauna 

 of such comparative poorness. Amongst its most 

 important gaps may be mentioned the entire 

 absence of the thoroughly Palacarctic Sylvinae. 

 In every part of these two mighty areas, from 

 the highest Polar land yet visited by man, down 

 to Mexico, Algeria, Northern Persia, the Yangtse, 

 and Japan, migratory birds come from the south 

 in spring to breed, and return to the south in 

 autumn to winter. The migration flight of 

 course varies to a very great extent, reaching for 

 10,000 miles or more in the most northern species, 

 and dwindling down to perhaps a couple of 

 thousand, or even one thousand, amongst the 

 most extreme southern species. It now becomes 

 necessary, owing to different climatal conditions, 

 to speak of each of these great regions separately. 



The great winter quarters of Palaearctic migrants 

 are in Africa, India, South China, the Siamese 

 Peninsula, the Malay Archipelago, Australia, and 

 New Zealand. Birds visiting the West Palaearctic 

 region, at least as far east as the Urals and the 

 Obb valley, normally winter in Africa and Turkey 

 in Asia, but a few retire to India, and a few to 



