42 INTRODUCTION. 



are required of them. They are also apt to be broken or torn 

 in the flights, the wars, and the labours of their owners. They 

 are therefore periodically shed and reproduced ; and the repro- 

 duction usually takes place in such a way, so that the bird shall 

 be in best feather at the very time when it has the greatest 

 labour to perform. 



The resident native birds of countries where the heat of the 

 year is comparatively uniform, moult gradually, and the same 

 may be said of those that have their Haunts in regions that are 

 always cold, and where the food is comparatively limited. Such 

 birds are seldom so denuded of feathers as to be unfit for pretty 

 vigorous flight. Birds which migrate from region to region moult 

 more periodically ; and in places where the migration is exten- 

 sive, it will perhaps be found, upon further examination, that the 

 bird moults twice in a year, though in most instances the spring 

 moult is less general than the autumnal one, being in many 

 birds, the males especially, rather a change of colour than of all 

 the feathers. Birds which migrate polar ly, or for the purpose 

 of breeding, generally receive their nuptial colours, if not their 

 plumage, after they arrive ; but when they migrate equatorially, 

 they change their plumage before they begin their journey. The 

 vernal change in the plumage of birds is owing to the same cause 

 as the change of their voices, from the chirp or cry to song ; and 

 in a state of nature the two cease together. 



HABITAT AND MIGRATION OB BIRDS.* 



THE habitat of birds is not circumscribed within such narrow 

 limits as that of quadrupeds, because, by means of their win^s, 

 they can traverse more space, and even cross the seas. The 

 aquatic birds, by alternate flying and swimming, can proceed to 

 the most remote countries. "Nevertheless, each species adopts a 

 country, chooses a climate suitable to its nature, and when the 

 change of season obliges it to seek, under new skies, a country 

 analogous to its former one, it is but for a season, These birds 

 always return to their favourite country at the season of repro- 

 duction. The Stork, indeed, has two separate broods, one brought 

 forth in Europe, and the other in Egypt. 



Birds, generally speaking, appear to belong more to the air 

 than to the earth. They constitute moving republics, which 

 traverse the atmosphere at stated periods, in large bodies. These 

 bodies perform their aerial evolutions like an army, crowd into 

 close column, form into triangle, extend in line of battle, or dis- 

 perse in light squadrons. The earth and its climates has less 

 influence on them than on quadrupeds, because they almost 



* Abridged from Griffith's Cuvier, vol. vi. p. 149. 



