THE PRACTICAL VALUE OF BIRDS. 1 



of Nature's immutable laws and a sad disarrangement of .her adjustments, 

 which can only be disastrous. 



True, in the rapid settlement of a new country it is impossible to avoid 

 a disturbance of the equilibrium, by destroying breeding places and food 

 supplies of certain species in bringing land under cultivation, and at the 

 same time providing better breeding places and food supplies for other 

 species. This, however, does not excuse unnecessary disturbance of natural 

 conditions by deliberately destroying useful species. It makes it even more 

 imperative that all species not known to be actually harmful be given an 

 opportunity to restore the equilibrium. Much is found in the past history of 

 agriculture in America to indicate that trouble with various pests is likely 

 to immediately follow the extension of agriculture into new regions, but that 

 in time readjustment takes place. It should be our aim to aid, rather than 

 to hinder, Nature in the accomplishment of such readjustment. 



It has been urged as an objection to the preservation of birds, that 

 many species of insects are predatory or parasitic; that such species destroy 

 other species of insects, and hence are themselves useful ; that birds eat the 

 useful insects, as well as the harmful ones. This same argument applies 

 with equal force to the use of sprays and other artificial methods of keeping 

 insect pests in check. Sprays and fumigants destroy useful as well as harm- 

 ful species. Beal (4) conclusively answers the argument by pointing out 

 that if, for example, one-half of the individuals of each species of insect 

 were destroyed, it would leave entirely undisturbed the "internal relations 

 of the insects among themselves." In other words, the various species would 

 still bear the same ratio to each other. The preservation of the balance is the 

 service rendered. 



The rate of increase of some insects is almost inconceivable. Dr. Mur- 

 ray (5) estimates that the increase from a single house fly, allowing only 

 one out of every 12 eggs to develop would reach the almost incredible number 

 of 7,600,000,000 from April 10 to September 10, only 5 months. Were it not 

 for their active enemies of all kinds, parasitic and predatory, insects would 

 soon increase to such an extent as to be destructive of all vegetation. 



The same may be said 'of pernicious rodents. Field mice have from 6 

 to 13 young at a time, and from 2 to 6 litters per annum (6). Were it not 

 for the hawk?, owls, weasels, snakes and other animals constantly feeding 

 upon them thoy would soon render agriculture hopeless. 



Many species which under normal conditions are useful, or at least 

 harmless, may . become very harmful if not kept in check by their enemies. 

 Probably under natural conditions no species is altogether harmful. Fruit 

 trees usually put forth more fruit buds than can mature into choice fruit, 

 and often more foliage than is really advantageous. Insects in reasonable 

 numbers to carry on the work of budding the trees early in the season may in 

 many cases be useful, but if they greatly increase in numbers they would 

 become harmful. When they become too numerous they have been known 



(4) Beal, F. E. L., The Relations Between Birds and Insects, U. S. Dept. Agric., 

 Yearbook for 1908, p. 350, 1909. See also Forbes, S. A., Illinois State Lab. Nat. Hist., 

 Bull., Vol. I, No. 3, pp. 90-93. 



(5) Popular Mechanics, June, 1912, p. 793. 



(6) Piper, Stanley E., The Nevada Mouse Plague of 1907-8, U. S. Dept. Agric., 

 Farmers' Bull. No. 352, 1909 ; Mouse Plagues, Their Control and Prevention, U. S. 

 Dept. Agric., Yearbook for 1908, p. 303, 1909. 



