164 CONSERVATION OF CANADIAN WILD LIFE 



under the snow, under which they are accustomed to shel- 

 ter, but which proves to be a death-trap when alternate 

 thawing and freezing causes the formation of an ice-crust. 

 The most important and at the same time the most in- 

 teresting cause of the scarcity of grouse during recent 

 years has been the migration southward of certain large 

 species of northern predatory birds such as the goshawk 

 and great horned owl. This southern migration of these 

 predatory birds was evidently due to the scarcity through- 

 out the northern regions of the rabbit or varying hare, 

 which experiences, as is well known, periodic cycles of abun- 

 dance and scarcity, as I have described in another chapter 

 (see p. 216). This relation between the scarcity of rabbits 

 and the decrease in the numbers of grouse was indepen- 

 dently studied by Mr. P. A. Taverner and myself in Canada, 

 and Mr. John B. Burnham, president of the American Game 

 Protective Association, who has published an interesting 

 report on the subject.* Owing to the scarcity of rabbits, 

 which normally constitute the chief food of such predatory 

 birds as the goshawk and great horned owls, these birds mi- 

 grated southward in large numbers and sought other prey. 

 This migration brought these enemies of our game-birds 

 in abnormal numbers into the natural haunts of the various 

 grouse, and these birds suffered from the consequent ex- 

 cessive slaughter. In cases of this kind the natural balance 

 usually becomes restored in a few seasons, and, if close sea- 

 sons are wisely fixed to counteract the baneful influences of 

 natural factors over which we have no control, it is possible 

 to prevent excessive reduction in numbers provided steps 

 are taken at the same time to prevent overshooting. These 

 species of grouse afford such excellent sport and recreative 

 exercise that the greatest care should be taken in the fixing 

 of open seasons, bag limits, and in regulating the methods 



* Bulletin of the American Game Protective Association, vol. VII, no. 1, 

 pp. 4-8, January, 1918. 



