176 THE STORY OF THE BIRDS 



example. This means a journey from some 

 southern land to a northern one for the summer, 

 and a return to the winter home in autumn. 

 Then we have what is termed Vertical Migration, 

 in which certain birds leave the lowlands and 

 plains in spring, and seek summer quarters high 

 up the mountains, it may be (and mostly is) 

 without leaving a country or crossing the sea 

 at all. This kind of migration is very prevalent 

 in warm countries. Indeed some few British 

 species — birds that visit us in summer — are verti- 

 cal migrants in more southerly localities, finding 

 suitable summer quarters by elevation rather 

 than by latitude. Then we may briefly allude 

 to the various local movements of birds, usually 

 undertaken during the non-breeding season. 

 These can scarcely be classed with regular 

 migration, because they are without any ap- 

 parent system or method, prompted solely by 

 a desire for food, and in all cases take place 

 within the normal area of dispersal of the species 

 engaging in them. The most pronounced kind 

 of local movement may be classed as Nomadic 

 Migration, usually prevailing among birds that 

 live in cold regions, and which are wander- 

 ing about almost all the year except when en- 

 gaged in rearing their young. Within certain 



