MIGRATION 99 



by a great band of Nutcrackers {Nucifraga caryocatactes). But 

 nothing whatever on this head is known. 



And this brings us to the question — Why do birds migrate ? 

 To attempt an answer to this question is, at present, to attempt 

 a very difficult task. But before proceeding to make the en- 

 deavour it would be well to draw attention to one or two further 

 mysteries of migration which have long excited the comments 

 of Ornithologists but as yet defy all attempts at solution. 



Why, for example, in so many species do males usually 

 arrive in advance of females ? This is true of the Warblers, for 

 example, males of which reach their breeding quarters some 

 days in advance of the females. More extraordinary still in a 

 large number of species, the adults leave before the young birds, 

 while with the Swallow the young leave first, undertaking their 

 stupendous journey without guides. That is to say, birds which 

 have but recently left the nest are left to find their way, ap- 

 parently unaided, to the winter quarters in Africa ! The young 

 Cuckoo, for example, accomplishes this feat, and so also, ap- 

 parently, do the young of the Red-backed Shrike. 



Yet another remarkable feature of our annual migrants is 

 the wonderful regularity with which they make their appearance 

 and disappearance. Thus of the Puffin {Fratercula arctica) 

 Professor Newton wrote : " Foul weather or fair, heat or cold, the 

 Puffins repair to some of their stations punctually on a given 

 day as if their movements were regulated by clockwork. 

 Whether they have come from far or from near we know not, 

 but other birds certainly come from a great distance, and yet 

 make their appearance with scarcely less exactness." 



Such, in brief outline, are the main features of the migration 

 of birds. In the space of a single chapter no room can be found 

 to describe the laborious work that has been expended on this 

 subject by workers abroad, nor of the splendid work of Barring- 

 ton and Eagle Clarke and others in Great Britain. During the 

 last year or so some most valuable work has been done by a 

 committee of the British Ornithologists Union, the aim being 

 to gain an insight into the lines of migration and dispersal in 

 Great Britain ; and it is certain that if this work is carried on 

 most important results will follow. But we are yet as far off 

 as ever with regard to the crux of the whole matter — Why do 

 birds migrate ? 



