USEFUL BIRDS. 



they may bear to the unnatural and semi-artificial conditions 

 produced by the agriculturist may then be better under- 

 stood. The position occupied by birds among the forces of 

 nature is unique in one respect at least ; their structure fits 

 them to perform the office of a swiftly moving force of 

 police, large bodies of which can be assembled at once to 

 correct disturbances caused by abnormal outbreaks of plant 

 or animal life. This function is well performed. A swarm 

 of locusts appears, and birds of many species congregate to 

 feed upon locusts. An irruption of field mice, lemmings, or 

 gophers occurs, and birds of prey gather to the feast from 

 far and near. 



This habit of birds is also serviceable in clearing the earth 

 of decaying materials, which otherwise might pollute both 

 air and water. A great slaughter of animals takes place, 

 and Eagles, Vultures, Crows, and other scavengers hasten to 

 tear the flesh from the carcasses. A dead sea monster is 

 cast upon the shore, and sea birds promptly assemble to 

 devour its wasting tissues. The gathering of birds to feed 

 is commonly observed in the flocking of Crows in meadows 

 where grasshoppers or grubs abound, the assembling of 

 Crows and Blackbirds in cornfields, and in the massing of 

 shore birds on flats or marshes where the receding tide 

 exposes their food. 



A study of the structure and habits of birds shows how 

 -well -fitted they are to checli excessive multiplication of 

 injurious ci'eatures or to remove offensive material. Birds 

 are distinguished from all other animals by their complex, 

 feathered wings, — the organs of perfect flight. 



The tremendous muscular power exhibited by birds is only 

 such as might be expected in creatures provided with such 

 perfect respiratory, circulatory, and assimilative organs. The 

 strength of birds as compared with that of man is enormously 

 out of proportion to their size ; but it is largely concentrated 

 in the muscles that move the wings, for it is by flight that 

 the bird is enabled to live. No other animals have such 

 sustained power of flight or such perfect command over 

 themselves while in the air. Even the bat, which is a most 

 skillful flyer, being remarkably quick in 'aerial evolutions, 



