204 THE MIGRATION OF BIRDS. 



spreading northwards, from Africa, India, or China, 

 for instance, right across Europe and Asia to the 

 Arctic regions. All the various important Routes of 

 Migration are more or less thronged with journeying 

 birds ; and at the intermediate stations famous for 

 Flight, species after species appears at its usual time 

 and passes on. At Gibraltar, along the chain of 

 the Atlas mountains, at Malta, in the Greek 

 Archipelago, in the Nile Valley, along the Red Sea, 

 and at the great passes of the Himalayas, as w^ell 

 as up the Chinese river valleys and coast-lines. 

 Birds in countless hosts are quietly pressing on — 

 all with one common purpose in view, that of 

 reaching their nesting-places as quickly as possible 

 and settling down to family duties. As each 

 species, or the individuals of each species, reach 

 their haunts, the Great Avian Wave gradually 

 decreases ; the further and further north it fiow^s 

 the number of species become less, until all but the 

 most Arctic ones remain. 



Some species for reasons at present quite 

 inexplicable follow a different route in spring from 

 that which they traverse in autumn. This is 

 proved by the foUow^ing facts. The Nightingale 

 {Erithacus luscinia) passes over Heligoland in April 

 and May, but has never been caught there in 

 autumn ; the Dotterel {Eudromias morinellus) is 

 rarely or never seen in Malta in spring, but passes 

 that island regularly enough in autumn ; the 

 Turtle Dove (Turtur auritus) passes Heligoland 

 commonly in May and June, but is much less 



