204 The Ruffed Grouse 



by this bird. Since many of the signs could not be distinguished with 

 complete accuracy from those of other hawks and owls, this figure 

 is only approximate. It is regularly somewhat over fifty per cent of 

 grouse adult losses from all causes. 



While the prominence of the homed owl as a predator of grown 

 grouse far overshadows its indirect effect on nests, a considerable 

 number of grouse eggs are lost due to the owls killing the mother 

 bird. On Connecticut Hill about one in twenty-five of the nests 

 destroyed was attributed to avian predators, largely this species of 



owl. 



We have already noted that predators are not a primary cause of 

 mortality among the young grouse in the summer. No doubt the 

 homed owl takes a small toll then, but the fact that feathers of 

 very young grouse are not left in the woods but are consumed with 

 tlie birds, makes an accmate survey of the owl predation impossible. 

 Some remains of immature grouse have been found in horned owl 

 pellets and the feather remains of a few have been taken as evidence 

 of horned owl killings. It is probable that this species ranks next, 

 after the sharp-shinned and Cooper's hawks, as a destroyer of young 

 grouse. 



We have seen that the foxes, though veiy important as grouse 

 predators, do not depend upon them for a high proportion of their 

 food. This is also tme of the great homed owl. Although first among 

 the predators upon adult ruffed grouse, it still does not make a very 

 high percentage of its food of grouse. We must again conclude, 

 therefore, that the proportion of a predator's food composed of a 

 given prey species does not necessarily measure, or even indicate, 

 the place that that predator plays in the ecolog)' of the prey species. 



Typical of the records of horned owl food habits are those sum- 

 marized by McDowell ( 1940 ) . Ruffed giouse made up one and nine- 

 tenths per cent of the whole diet of the nine hundred and eighty- 

 three owls examined. They were taken between November and May. 

 The grouse were found in only fourteen of the stomachs, or one and 

 four-tenths per cent of the total, and were far outranked by a num- 

 ber of other prey species, mainly rodents. Errington, Hamerstrom 

 and Hamerstrom (1940) examined four thousand, eight hundred 

 and thirty-eight pellets from Iowa and Wisconsin and found twenty- 

 two of them, or five-tenths of one per cent, to contain remains of 

 ruffed grouse. They say: "Ruffed grouse . . . populations in the 



