PESTS AND THEIR TREATMENT 131 



There should be inaugurated a general movement 

 for the planting of these trees. 



Our second subject relates to the species of birds 

 and mammals that usually are harmless, but under 

 exceptional local conditions sometimes become 

 pests that require abatement. 1 



The principle involved is best explained by 

 examples. The most world-famous case is that of 

 the introduction of the European rabbit in Aus- 

 tralia. Under the restrictions imposed by hunters, 

 poachers, hawks and owls in densely populated 

 England, the English hare is so scarce as to be 

 harmless. In Australia, with abundant food, a 

 hospitable climate and practically nothing to keep 

 the species in check, it multiplied to such an extent 

 as to constitute an intolerable pest. In southern 

 California, Texas and Oklahoma, the wild jack- 

 rabbit in the same manner once increased so 

 enormously that wholesale killing measures became 

 necessary to keep down the total. 



In one locality in the state of Oregon, eagles once 

 became so numerous that their depredations on the 

 lambs of the flocks of the sheep-owners became too 

 great to be borne. When the case was laid before 



i The crow has long been fought over, by a small minority that 

 recounts his wrong-doings and demands his blood, which is opposed 

 by an overwhelming majority that recounts the bird's good deeds 

 and resolutely prevents his being slaughtered. It is perfectly true 

 that some of the ways of the crow are very trying; but when all the 

 evidence has been brought in and weighed and measured, the good 

 deeds of the crow in devouring grasshoppers, cutworms and other 

 bad insects, meadow mice and other bad rodents, are so many that 

 Corvus seldom is condemned to wholesale destruction. 



