CONCLUDING REMARKS. 97 



quently, a wholesale destruction of the farmer's crops 

 would be the inevitable result. In every fauna left to 

 itself, or but slightly disarranged by man, "a certain 

 balance of forces is sooner or later established tending 



c^ 



to the co-ordination and subordination of various forms 

 of animal life." 



Every species has a natural check to undue multipli- 

 cation. When propagation has reached a certain limit, 

 farther increase is stayed by natural conditions. Either 

 the supply of food becomes diminished and thousands 

 perish, the stronger alone surviving in the " struggle 

 for existence, 7 ' or else the overgrown species affords an 

 extra allowance of food to its natural enemies which 

 have waxed powerful enough to reduce the threatened 

 numbers. 



In America the birds exist under unnatural conditions. 

 They are out of place. Their remarkable increase should 

 not excite astonishment. Other instances than this 

 could be cited to show the reaction of exotics upon the 

 natural species. The Norway rat, which was introduced 

 into this country many years ago, is destined to usurp 

 the place of our native species. There are but few 

 localities where the latter exists. Its hardy and pugna- 

 cious relative from the north of Europe, is slowly but 

 surely supplanting it. Among plants, the white weed 

 has overrun the entire country, and choked out native 

 vegetation. Even the Indian, who once inhabited the 

 whole of North America, is fast receding before the 

 rapid advances of the energetic European, or his de- 

 scendants. 



The sparrow is rapidly exterminating the native song- 

 sters and insect-eating birds from our cities and large 

 towns. Even in many rural districts the same condition 



