STRANGERS OF THE AUTUMN. 195 



attended with doubt. When we know that these 

 distinguished strangers occur from time to time 

 on Heligoland, we consider it very probable that 

 others of that particular species may come across 

 to us with the regular stream of migrants ; for 

 there is an enormous passage of birds over this 

 favoured little spot to the British Islands every 

 autumn. Any bird that may chance to wander to 

 Heligoland may therefore just as likely pay us a 

 visit too. On the other side of the Atlantic, the 

 Bermudas and the Azores may be aptly termed 

 the American Heligoland ; and practically all the 

 New World birds which have visited the British 

 Islands, the genuineness of whose occurrence is 

 not open to doubt, are more or less regular birds 

 of passage over them in autumn or spring. 



In order to understand the philosophy of this 

 bird errantry still farther, it is well to point out 

 what a great number of strictly West Palaearctic 

 birds reach the limit of their eastern range in the 

 valleys of the Yenesay, and possibly the Lena, 

 in Central Siberia. Most of the birds that travel 

 so far east in spring, return to South Europe and 

 Africa to winter ; consequently, there is a very 

 important stream of migration in this direction in 

 autumn, which drains off a few of the strictly 

 Asiatic species whose proper destination at that 

 season is Turkestan, Persia, India, China, the 

 Burmese Peninsula, and Australia. During the 

 last glacial epoch, the entire bird population of the 

 -northern parts of the Eastern hemisphere was 



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