ROLE OF PREDATION 



311 



something far more fundamental than mere conflict between individuals was emphasized by 

 Huxley*. 



"I suppose that most professional biologists think of the relation of carnivores to herbi- 

 vores, preyer to preyed-upon, almost wholly in the light of the familiar metaphor of 

 enemies; and of the relation between the two as being in some real way like a battle. 

 The ecologist, however, speedily arrives at the idea of an optimum density of numbers, 

 which is the most advantageous for the animal species to possess. He then goes on to 

 see by what means the actual density of population is regulated towards the optimum; 

 and finds that in the great majority of cases the existence of enemies is a biological 

 necessity to the species, .... To have the right 'enemies', though it can hardly be 

 spoken of as an adaptation, is at least seen to be a biological advantage." 



Such is the role played by predation in the ecology of the ruffed grouse. Yet this factor 

 is not a static influence, exacting its "pound of flesh" inexorably year in and year out. Rather 

 its effect in any covert is in a constant state of flux depending on the relative abundance of 

 the grouse and its various predators and buffers, as well as the weather, the amount of hunt- 

 ing done and innumerable other conditions. 



Effect During Each Life Period 



Throughout its range the grouse is subject to essentially the same pattern of predation. 

 Beginning with the breeding season the losses mav be Iogirall\ divided into three categories 

 corresponding to the major life periods of the bird, namely, nest, brood and adult. 



Nest Period 



Although reduction of the possible productivity each season commences with unsuccessful 

 breeding in terms of unmated females and infertile eggs, nesting failure represents the first 

 major loss during most years. Since nest sur\'ival data could be recorded without conducting 

 supplementary population censuses, material was gathered throughout the State in addition 

 to the study areas. From 1930 through 1942 a total of 1.431 nests were examined by the 

 Investigation for which survival figures are comparable'^. In each case the fate of the nest 

 was noted and for those which had been broken up a diagnosis of the cause responsible 

 was made. Table 35 presents the results with respect to total losses and the proportion attri- 

 butable to predation. Tlie reliability of the percentages for the years 1930 and 1942 is ques- 

 tionable due to the small number of records. 



TABLE 35. GROUSE NEST IMORTAI.ITY HECORDED IN NEW YORK STATE 

 PROPORTION RESULTING FROM PREDATION— 1930-1912 



* Incliuies only nests for wliich survival data are comparable. 



AND 



* In Elton. Charle9i23. 



A Infnrmation nxht-x ihan survival lias been senired for a larnc nunihiT of additional nests, particularly ihnse tak<Mi for propaga- 

 tinii. Tims titbles appearing elaewlicre in the book, particularly in Chapter III, involve a greater total during some years. 



