254 Cameron, The Golden Eagle in Montana. \.^uU 



its force is greatly weakened by two considerations which give a 

 somewhat different complexion to Mr. Oberholser's results. In 

 the first place it must be remembered that the "balance of Nature" 

 is maintained by relatively few survivors out of the total number 

 born. " Heavy destruction," to use Darwin's classical phrase, 

 "inevitably falls either on the young or on the old during each 

 generation and at recurrent intervals." Birds of prey or epidemic 

 disease are the necessary complement of grouse. In England we 

 have extinguished the birds of prey and our plethoric grouse moors 

 are periodically swept by a pestilence. With all rapidly increasing 

 species, whether of fur, fin or feather, a periodical destructive agency 

 is not only necessary but beneficent. The eagle is replaced by 

 the bacillus. 



In the second place, Mr. Oberholser's figures rest on the as- 

 sumption that all the Montana eagles live on grouse; but this is 

 a mistake, and his estimated eagle grouse-bag may therefore be 

 considerably reduced. As pointed out by Mr. Frank M. Chap- 

 man: "A bird's food habits may vary so greatly with locality 

 that it is as deserving of protection in one place as it is unworthy 

 of it in another." ^ All my observations and enquiries show that 

 Golden Eagles invariably feed themselves and their nestlings 

 upon whatever prey is most convenient to their eyrie. Thus 

 many pairs take very few game birds. For example, large prairie 

 dog towns constitute the domain of the Knowlton eagles, and, in 

 striking contrast to my Fallon pair (which never captured a prairie 

 dog), they subsist almost exclusively upon this rodent. AVhereas 

 I never visited the badland eyrie without finding one or more 

 Sharp-tailed Grouse, the Knowlton nest, on the other hand (which 

 I examined two or three times a week), always contained one, and 

 occasionally two prairie dogs. Now, the destruction of prairie 

 dogs is of the greatest benefit to the settlers, as in this locality 

 (Knowlton) they have increased to an alarming extent. On 

 some ranches the rodents play havoc with the crops and "dog 

 towns" have encroached upon miles of good grazing land, reducing 

 it to a desert. The burrows also constitute a serious menace to 

 fast riding horsemen. It is only necessary to read the forcible 



' Bird Lore, November— December, 1906. p. 213. 



