310 The Ruffed Grouse 



ties. And finally the grouse themselves affect each other's survival 

 by their fighting, courting, and other relations. 



We cannot unravel all of these many involved relations of grouse 

 ecology. Even if we could, we would surely find that all must be 

 considered in evaluating tlie needs of the species, and in translating 

 them into management. No one aspect of the maze can get far out 

 of balance without seriously affecting the whole. 



Pervading all grouse environmental needs as of first importance 

 is habitat: food, and shelter. The cover definitely delimits the possi- 

 bility of grouse inhabiting any portion of the range. Within the 

 framework of acceptable cover, all of the other factors and influ- 

 ences combine to determine the level of the grouse population. 



Cycles of Abundance. A cycle, according to the dictionary, is a 

 round of operations or events— a series which returns upon itself. 

 A recent adaptation of this usage in connection with animal popula- 

 tions refers to changes in numbers of a species that take place regu- 

 larly according to uniform time intervals, and usually include a pre- 

 cipitous decline phase. During this decline, the species may lose up 

 to ninety per cent or more of its members in a relatively short time. 

 Species that are thus regular and violent in their population changes 

 are said to be cyclic species. The ruffed grouse has been among the 

 group so classed. 



The general concept of an animal population cycle is that an 

 abrupt drop in numbers occurs some time after the species has 

 built its population up to carrying capacity— i.e., all tliat the environ- 

 ment can support. In some cases this carrying capacity level is tem- 

 porarily exceeded, thus assuring a quick and large drop in num- 

 bers. The size of the population itself may bring about its down- 

 fall through the medium of some mass-decimating agency; in this 

 case the regularity of the cycle would be due to the constancy of the 

 time required to bring the population to the critical level. It may be 

 that the periodicity is involved in a factor that is independent of 

 the animal population in question. Such might be the case ff years 

 of sunspot maxima, which themselves occur in cycles, brought about 

 some environmental influence which caused catastrophic decima- 

 tion regardless of the position of the population level at the time. 



That these two types of cycles exist in nature, no careful student 

 of the subject can deny. Whether or not ruffed grouse populations 

 adhere to any such biological or physical laws is another matter. 



