THE AUTUMN MIGRATION OF BIRDS. 231 



eastern haunts owing to the climate being much 

 more rigorous than in Western Europe, where the 

 influence of the Gulf Stream renders the winters 

 comparatively mild and genial. This great wave 

 of hardy autumn migrants probably begins to flow 

 westwards from the valley of the Yenesay, and 

 drains a strip of country, perhaps 1000 or 1500 

 miles wide, gradually spending itself in Western 

 Europe and the British Islands, where many of 

 these migrants pass the winter. The route followed 

 appears to be by way of the Aral and Caspian Seas, 

 along the lower valleys of the Volga and the Don, 

 the northern coasts of the Azov and Black Seas, 

 and the valleys of the Dnieper and Danube. Pro- 

 bably throughout its course contingents of birds 

 are from time to time leaving the main artery, and 

 fiying south into Persia, Asia Minor, Turkey, 

 Greece, and Italy, as more or less important influxes 

 of the birds forming this stream are remarked at 

 that season in those countries. Many odd in- 

 dividuals of eastern species, whose proper line of 

 migration is south or south-east, get into this 

 western stream of birds and are borne into Western 

 Europe, some of them even reaching the British 

 Islands, Heligoland, and other localities. These 

 lost stragglers are very important indications of 

 this western Migration in autumn. Some of them 

 belong to southern species, but their summer area 

 extends for a considerable distance north in Asia, 

 say into Turkestan and the extreme south of 

 Siberia. Now no northern Migration is known in 



