Interrelationships of Ruffed Grouse 219 



to be a possible correlation in the 1936 decline in grouse take, which 

 coincided with decreases in the take of foxes and gray squirrels and 

 with the completion of the reduction in take of cottontails that had 

 begun two years prior ( see Fig. 9 ) . 



So many factors enter into these population trends, and they are 

 of such varying importance, that it would not be expected that the 

 population curves of so many animals would agree in details. There 

 is enough evidence from the data, though, to support the interrela- 

 tion theory among these populations. In Fig. 10 we have tried to 

 generalize the data in order to illustrate what appears to be the cor- 

 relation. The rodents lead the parade, and change most violently; 

 the predators and giouse follow with less marked changes. 



OTHER ANIMALS THAT AFFECT THE GROUSE WELFARE 



Predators and their usual prey, the buffer species, are not the only 

 mammals that influence grouse. Many mammals, and birds too, 

 compete with grouse for food, although this does not ordinarily 

 cause much trouble ( see page 178 ) . However, those mammals that 

 graze or browse can have a seriously detrimental effect on the wood- 

 land cover. Over most of the grouse range, the white-tailed deer is 

 the only one that becomes abundant enough to damage the range. 

 The Pennsylvania deer problem, much publicized in the past two 

 decades, will serve as an example. Leopold (1943) in discussing this 

 situation says: "Many plants important to other game species were 

 also depleted; thus greenbrier, on which ruffed grouse depend for 

 cover, was nearly annihilated. Snowshoe hare and wild turkey like- 

 wise felt the pressure of excess deer." 



PREDATION AS A LIMITING FACTOR 



Throughout the discussion of the relations of grouse populations 

 to other animals, it has been apparent that predation is normally a 

 constant and immediate medium of reduction of grouse, either as 

 eggs or birds. The manifestation of predation does not, however, 

 necessarily measure its status as a limiting factor, or potential limit- 

 ing factor. However, it does deserve the most careful analysis in 

 comparison with other major factors. Any group of organisms that 

 normally destroy two eggs out of every five laid by a prey species, 



