Our Balanced World 539 



mice, and weed seeds, or when they act as scavengers. They are 

 harmful when they eat grain, fruit, and fowl. 



The Division of Biological Survey connected with the Depart- 

 ment of Agriculture reports that a large number of birds, formerly 

 considered undesirable because they were supposed to destroy 

 much grain, are on the whole useful, since they kill vast numbers 

 of insects that feed on vegetation. These include swallows and 

 starlings. Even the crow has something said in its favor. 



Among birds that are useful as killers of rodents are owls and 

 hawks of various kinds. Cooper's hawk, the sharp-shinned hawk, 

 and the great horned owl are considered harmful, since they are 

 enemies of birds and poultry. As all birds must have food to 

 survive, they should be judged by the net result of their 

 work. Any bird that is more useful than harmful should be pro- 

 tected. 



Rats. Of all the mammals in the world, rats are the most 

 harmful to man. Because they live in drains, sewers, and other 

 filthy places they are often the carriers of the germs of infectious 

 diseases. Rats also harbor on their bodies fleas that are some- 

 times carriers of the germs of the dread bubonic plague. For 

 this reason special steps are taken in our ports to prevent the 

 escape of rats from ship to shore. 



Rats are also great destroyers of property. It is estimated 

 that rats in this country alone destroy over $200,000,000 worth 

 of grain in a single year, besides doing enormous damage to 

 property of other kinds. 



Fishes and Other Sea Creatures. Fishes are a great source 

 of food for man. Every year millions of pounds of salmon are 

 taken from rivers flowing into the northern Pacific, and vast quan- 

 tities of cod, haddock, mackerel and other food fishes from the 

 waters of the Atlantic. In addition, a vast business is carried on 

 in the catching and selling of edible fresh water fish. Modern 

 refrigeration methods enable us to ship large quantities of fresh 

 fish to all parts of the country. The balance of the catch is pre- 

 served for future use by canning, salting, and drying. Aside from 

 the fishing industry, there is sport fishing which supplies recreation 

 for millions of people. 



