I04 THE MIGRATION OF BIRDS. 



Oder, the Elbe, and the Rhine, which connect with 

 the Danube system, which leads on to Turkey, 

 Greece, and the East Mediterranean sea routes, 

 and along which many of the migrants from the 

 East to the British Islands and from Scandinavia 

 journey to and fro. In Africa, which is practically 

 a continuation of the direct routes from Europe, 

 the most important river highway is the Nile 

 Valley, which receives an incredible number of 

 migrants from Russia, Asia Minor, and Syria — 

 most of them species that winter far to the south 

 in that continent. The Niger Valleys, but on a 

 much less important scale, drain some of the 

 migration which spreads across North-west Africa ; 

 but in the west of the continent coast routes pre- 

 dominate. In Asia the great river valleys are 

 singularly well situated for migration, and the 

 number of birds that pass along them on flight 

 is past all belief. The migrations of almost every 

 species of migratory east Paleearctic birds may be 

 traced along them. The three great northern 

 river-systems are those of the Obb, the Yenesay, 

 and the Lena. Not only do the main valleys of 

 these vast waterways favour a direct flight towards 

 the winter quarters of birds due south of them, 

 but their endless south-westerly trending feeder 

 valleys favour the migration of those birds breed- 

 ing in the east Palacarctic region, and wintering in 

 the Ethiopian region. By these cross valley routes 

 many species whose eastern range in summer ex- 

 tends as far as the Yenesay (which is on the 



