90 THE COMING OF THE BIRDS 



more about this later. It had prodigious influence 

 on animal and plant life, as will be imagined after 

 our description of the Permian Revolution. This was 

 a far greater Ice Age. 



Bamboos and magnolias had long ago retired south. 

 Now, as the ice-sheet spread south as far as the valley 

 of the Thames and the Danube, the whole population 

 fled before it. The change was, as ususal, extremely 

 slow, and the reader will not misunderstand when 

 I speak of even the plant-world retiring before it. 

 Only the south of Europe and Africa — they were then 

 connected by land — now bore the wealth of flowers on 

 which the insects lived, and the birds followed their 

 food. Hardy types, the birds of the Arctic and 

 Antarctic, were evolved, but the vast majority 

 retreated with the warmth and the insects. 



Probably many features of our insects and birds 

 were developed during this long and severe trial. The 

 instinct of nesting would be fostered in the birds, and 

 probably it was then that the ants and bees developed 

 their elaborate ways of preparing against a "lean" 

 season. The migration of birds may also receive 

 much light from this geological event. It is known 

 that migrating birds do not simply fly "somewhere 

 south," where there are flowers and insects. Each 

 family has its winter resort, and they follow particular 

 and often curious routes to it. It is supposed that 

 they go back to their homes in the Ice Age, and they 

 follow routes which were at one time "all land" 



