MIGRATION OF BIRDS. 157 



this purpose. Birds have nothing of this nature 

 and make no provision for their young ; but they 

 of all creatures, except fishes, can seek what may 

 be required in distant stations with most facility. 

 A sufficiency of food for the adult parent may be 

 found in every climate, yet the aliment necessary 

 for its offspring may not. Countries and even 

 counties produce insects that differ, if not in 

 species, at least in numbers ; and many young 

 birds we cannot succeed in rearing, or do it very 

 partially, by reason of our ignorance of the re- 

 quisite food. Every one, who has made the 

 attempt, well knows the various expedients he has 

 resorted to, of boiled meats, bruised seeds, hard 

 eggs, boiled rice, and twenty other substances, 

 that nature never presents, in order to find a diet 

 that will nourish them ; but Mr. Montague's 

 failure in being able to raise the young of the cirl 

 bunting*, until he discovered that they required 

 grasshoppers, is a sufficient instance of the manifest 

 necessity there is for a peculiar food in one period 

 of the life of birds ; and renders it probable that, 

 to obtain a certain aliment, this willow wren, and 

 others of the insect and fruit-feeding birds, direct 

 their flight to distant regions, and is the principal 

 cause of their migrations. 



It is some stimulus like this, which urges that 

 little creature, the golden-crested wren (motacilla 



* Linnean Transactions, vol. vii. 



