BIRDS AS RELATED TO AGRICULTURE 197 



in the spring when insects are beginning to appear. This is. 

 a time when the destruction of insects gives the greatest 

 protection to crops. Many adult insects are killed before 

 they lay eggs, thus preventing in advance the damage a new 

 generation might do. Again, countless young caterpillars 

 and other insect larvae are destroyed before they are large 

 enough to do much injury. 



Bird population. The effect of the decrease in the bird 

 population in any agricultural region is shown almost im- 

 mediately by the rapid increase of insects. On the other 

 hand, injuries threatened by large numbers of insects are 

 soon checked by the appearance of birds. 



The importance of maintaining the bird population has 

 been recognized in most states by laws protecting song birds 

 and their nests. State laws have been greatly strengthened 

 lately by national laws, both of the United States and of 

 Canada, which are intended to protect birds during their 

 migration periods. 



A bird census or survey which was conducted in 1914 and 

 again in 1915, under the direction of the U. S. Department of 

 Agriculture, indicates that the kinds of birds, as well as 

 individuals of each kind, are less numerous on farms than 

 they should be for adequate protection against insects. 

 These surveys show approximately an average of one pair of 

 birds to each acre of farm land, an average much too low for 

 the protection of crops. The facts of bird life, as shown by 

 many observers in various parts of the country, point to a 

 decrease in the bird population ranging from ten to seventy- 

 five per cent in thirty states. It is not enough merely to 

 protect birds from wanton slaughter. Some measures need 

 to be taken to increase the number of birds, especially on 

 farms. Among the things which encourage the presence of 



