128 MIGRATION OF BHIDS. 



subsistence, and are thus capable of living at all seasons 

 of the year, the birds must subsist upon soft substances, 

 as insects and their larvae, or the seeds, and green and 

 succulent leaves of plants ; while quadrupeds, being 

 furnished with organs of mastication which, along with 

 the saliva, reduce their food to a sort of pulp before 

 it be swallowed, can subsist upon dry leaves and 

 bark, and even upon twigs. Thus, in even the coldest 

 countries, there is still some food for a portion of those 

 quadrupeds that live upon vegetables ; and these again 

 afford subsistence for the carnivorous ones, as well as 

 for the more powerful birds of prey. In very cold 

 places too, the smaller quadrupeds, and even some of 

 the larger ones, are so constituted that they hybernate, 

 or pass the winter in a state of torpidity, in which they 

 have no necessity for food, and consequently none for 

 change of place. 



But in the severity of the northern winter, the food 

 of the feathered tribes fails. The earth and the waters 

 are bound up in ice, so that the worms and larvae are 

 beyond their reach ; the air, which in summer is so 

 peopled with insects, is left without a living thing; 

 the buds of the lowly evergreen shrubs, and those 

 seeds which have fallen to the ground, are hid under 

 that cold but fertilizing mantle of snow, which, cold as 

 it seems, secures the vegetation of the coming summer ; 

 the berries and capsules that rise above the snow are 

 soon exhausted ; and the buds of the alpine trees are 

 generally so enveloped in resin and other indigestible 

 matters, that they cannot be eaten. Thus the birds 

 must roam in quest of food : nor is it a hardship, it is 

 a wise provision. Were they to remain, and had they 



