132 MIGRATION OF BIRDS. 



west occasionally brings us an American visiter. The 

 flight of birds is therefore a sort of augury, though a 

 very different sort from that believed in by the super- 

 stitions of antiquity. It has no connexion with the 

 offices or fortunes of men, but it tells what kind of 

 season prevails in those climes whence the visiters come. 

 The early appearance of the winter birds is a sure sign 

 of an early winter in the northern countries ; and the 

 early appearance of the summer ones is just as sure a 

 sign of an early and genial spring in the south. 



The migration of our winter visitants is a very simple 

 matter ; we can easily understand why birds, when their 

 supply of food begins to fail, should fly off in a warm 

 direction ; but the return the general migration north- 

 ward for the purpose of rearing their young, is, at first 

 consideration, a more difficult matter. Yet when we 

 think a little, the difficulty ceases, and the one move- 

 ment becomes no more a miracle or a marvel than the 

 other. Very many of the summer birds feed upon 

 insects ; and summer insects are more abundant in the 

 northern regions than in the south. This happens 

 particularly with the water-flies, of which there are 

 supposed to be several generations in the course of a 

 long summer's day ; and the short night at that season 

 occasions little interruption to their production. The 

 same causes which produce the greater supply of insect 

 food, increase the daily period during which the bird 

 can hunt, and this gives it a farther facility of finding 

 food, over what it would have in the comparatively 

 short days farther to the south. But the breeding 

 time is that at which the birds are called upon for 

 extraordinary labour. During the period that the nest 



