THE INSURGENCE OF LIFE 165 



route for the White Stork in its southward or south-east- 

 ward autumnal flight. 



Some Fundamental Facts. — Migration is not to be 

 confused with the invasion of a new territory in search of 

 food and under pressure of increasing population — ^though 

 it may have originated in some cases in this way. It is a 

 regularly recurrent sea;sonal movement, — an oscillation 

 between summer- quarters and winter-quarters, between 

 a breeding and nesting place and a feeding and 

 resting place. And one of the fundamental facts is that 

 birds always nest in the colder area of their migratory range. 



For the Northern Hemisphere it must be admitted that 

 bird-migration is a general phenomenon, though it differs 

 greatly in its range and conspicuousness. In many parts 

 of Scotland the curlews pass at the beginning of winter 

 from the exposed moorland to the neighbourhood of the 

 sea-shore, where it is easier to procure food ; and flocks 

 of sixty or more of these shy birds are often seen at work 

 among the jetsam. This is migration within a short radius. 

 It may be contrasted with that of the Arctic tern which 

 the Scotia explorers found ' wintering ' in the Antarctic 

 summer in 74° S. lat. — ' the greatest latitudinal range of 

 any vertebrate animal '. 



It is said that many of the godwits which nest in eastern 

 Siberia winter in New Zealand, but the ' ringing method ' 

 should be used to test these generahzations. It is certain, 

 of course, that many godwits leave the north of New 

 Zealand in spring, that many godwits nest in Eastern Siberia, 

 and that many godwits return to New Zealand in October. 

 It is necessary, however, to prove that the birds that spent 

 some summer months in Siberia were the birds that enjoyed 

 in the same year a second summer in New Zealand. 



