ROLE OF PREDATION 



317 



On the other hand, losses experienced during the rest of the 

 attributable to predator activity. On the game farm mortality 

 old is negligible but in the wild moderate losses continue. The 

 more and more independent of the female with the result that 

 vulnerable to attack. The principal predators at this age, the 

 hawks (Accipiter cooperi and A. velox). were least affected by th 

 even here, there is some evidence that variations in the degree of 

 may often be traced to weather conditions*. 



summer seem more directly 

 after the birds are six weeks 

 chicks at this time become 

 they probably become more 

 Cooper's and sharp-shinned 

 e control experiments. Yet, 

 loss during July and August 



FEATHER REMAINS OF GROUSE CHICK KILLED BY A HAWK 



PROBABLY A SHARP-SHIN 



Considering all the data at hand it appears that upwards of one-third of the chicks hatched, 

 or a little over half of the total lost during the brood period in a normal season, have suc- 

 cumbed as a result of predation. The proportion, of course, varies with circumstances. 

 Furthermore, it represents a greater number of individuals during those years when the hatch 

 was higher. In other words, the more birds present the more frequently they are encountered 

 and caught. Major differences in total losses, however, have apparently been the result 

 of other influences despite the fact that predators may ultimately devour the birds. Thus 

 while this factor is important in determining brood survival it does not seem to have been 

 paramount, especially with respect to the occasional years of markedly high mortality. 



» Sec CliniiKT VI. p. 303. 



