BIRDS 107 



nested undisturbed in the previous summer, and fly to 



the north once more. 



This was repeated time after time. In a long period 



of time and certainly not without enormous numbers of 



victims, Nature fashioned a provident and hardy race of 



birds ; provident because they would fly south as soon 



as the cold set in, courageous because they ventured 



back to their old nesting-places in the spring. Natural 



selection further regulated the time of flight. The birds 



were not to start too early from the south, or they would 



find their old nesting-place still buried in snow : and not 



too late, or they would not have time to rear their young 



so as to be able to make the great migration. The young 



would accompany the older birds when they gathered 



for departure, and would observe the route so as to be 



able to teach it to their own young afterwards. And as 



those that would not make the flight at the proper time 



were always destroyed, there arose the species of 



migratory birds which still carry out their flight with 



such wonderful exactness.'^ 



'^A German ornithologist, Kurt Graeser, has recently given a different 

 theory of migration. He believes that the migratory birds are the 

 original type, and the non-migratory have descended from them. 

 According to him, the first birds lived on a very different land from 

 what we have now. It had enormous stretches of water, ice-fields, 

 steppes, and forests, which could give no food or shelter to the birds, 

 and had to be rapidly covered in order to reach places with plenty of 

 food. The primitive birds, therefore, must have had the instinct of 

 wandering restlessly and swiftly over the whole earth. Gradually the 

 birds would see that certain places were especially favourable for them. 

 They flew to these more and more, and from this habit was formed the 

 habit of definite migration. Later some of the birds found it better to 

 remain in one place, and were adapted by Nature as required. The 

 author believes that in time all birds would cease to be migratory, and 

 adapt themselves to a different diet and the privation it would entail. 



