MIGRATION AND INSTINCT 425 



appear to have developed into ouzels, which filled India 

 and the Malay peninsula, many of them migrating east- 

 wards to Java and the Pacific Islands, some even reach- 

 ing across the Pacific Ocean, and forming- a colony of 

 ouzels in Central America and north-western South 

 America. After the glacial period had passed away 

 from the North Pole, some of the ouzels seem to have 

 followed the ice northwards, and again to have spread 

 over Siberia, two species even reaching into and spread- 

 ing over Europe. 



Such is a brief outline, so far as we can oruess it from 

 the present facts of geographical distribution, of one of 

 the ofreatest emigrations or series of emiorations which 

 the world has probably ever known, and comparable only 

 to those of the Arvan race of men. The fact most 

 observable in these movements seems to be that birds 

 are guided by something very nearly approaching reason; 

 their habits are not merely the result of their capabilities ; 

 there is method in their mio^rations. Whilst we find that 

 a narrow channel is frequently the boundary of a bird's 

 distribution, we must admit that in most cases it is a 

 self-imposed boundary. It is not that the birds cannot 

 migrate across the sea ; the fact is simply that they do 

 not because they have no adequate motive. 



The more one sees of migration the less it looks like 

 an instinct which never errs, and the more it seems to be 

 guided by a more or less developed reasoning faculty, 

 which is generally right, but occasionally wrong. The 

 stream of migration which we watched for weeks whilst 

 waiting for the opening of navigation on the Yenesei was 

 almost always from due south to due north, but at the 

 commencement many parties of wild geese, too eager 

 to reach their breeding-grounds, overshot the mark, and 

 although the ice broke up at the rate of a hundred miles 



