6 INTKODUCTION. 



ripening fruits ; and, as that is the proper food of the larvae, 

 or caterpillars, of insects, these would appear in myriads, as if 

 they came by magic, or rode on the wings of the destroying 

 wind. Those reverses are part of the system of nature's 

 economy, and inseparable from a climate so variable, and, by 

 that means, so favourable to continual cultivation as ours ; 

 and they produce the most serious effects when they come 

 upon the vegetable tribes in the most active and vigorous 

 growth. Nor is there any season during which they would 

 not destroy the produce of the gardens and orchards, and 

 greatly diminish that of the fields, were it not for the birds. 



Almost all birds feed upon insects, molluscous animals, 

 (such as snails and slugs,) and worms, though many have 

 recourse to other food, particularly at certain seasons ; and 

 many retire from Britain when their favourite food becomes 

 scarce. But even those birds which feed upon the smaller 

 seeds are of service ; and the flocks which throng to the 

 corn-fields and pastures .during the winter, pick up the seeds 

 of various plants, which, if allowed to remain, would spring 

 up during the following season, and choke the more valuable 

 species. 



. The organs by which the various races of birds get at that 

 species of food which is best suited to their natures, are 

 admirably suited to the functions which they perform. If 

 the bird is to procure the larvae from the earth, as the rooks 

 do in clearing the land of those of cockchaffers and other 

 insect pests, the bill is formed like a sort of mattock, for 

 digging into the soil ; if the food be soft insects and their 

 caterpillars, the bill is soft and weak ; if seeds are part of the 

 food, the bill is of stronger form and firmer texture, in order 

 that it may clear the kernels of the seeds from their exterior 

 husks, which are either indigestible or afford very little nou- 

 rishment ; if the food is more strongly enclosed, as when it is 

 the kernel of a nut, or some insect or larva which burrows 

 under the bark or in the decaying wood of trees, then the 



