DIET 



219 



which buds and calkins are also the chief parts eaten is utilized fairly consistently. In this 

 are found the birches and maples. Then there is a third group, largely fruit-producers, such 

 as cherries, sumachs, strawberries, sedges and blackberries, which exhibit inconsistent and 

 substantial fluctuations in use by grouse over the 11 years. 



TABLE 29. YEARLY VARIATIONS IN PERCENTAGE BULK OF IMPORTANT FOOD 

 PLANTS OF ADULT GROUSE IN NEW YORK IN COMPARISON 

 WITH THE 11 YEAR AVERAGE 



*Coaibiaed, since the number present in a single year was too fewatu tabulate satisfactorily. 

 A Not recorded. 



Reasons for tliese variations are interesting but certainly still conjectural. Precipitation 

 and temperature conditions are probably basically responsible for fluctuations in the abun- 

 dance of many fruits. A shift in the carbon-nitrogen relationship is said to control a cycle of 

 approximately three years in the occurrence of beech mast. In years of plenty, the nuts are 

 eaten in large quantities, their very size being conducive to their bulking large in the birds' 

 diet. In non-beechnut years, however, the grouse fall back on other sources of food, notably 

 sumach, thornapple, cherry and aspen. In each of the years studied, the bulk supplied by all 

 four of these groups together was very similar. In 1934 the consumption of beechnuts was 

 about three times that of the subsequent two years, and products of the other three species 

 were eaten correspondingly less that year. 



As yet there is no satisfactory explanation for the yearly changes in consumption of the 

 always available buds. Though the study should be continued over a much longer period 

 before all conclusions can be stated with certainty, it seems clear that changes in utilization 

 are many times dictated not by availability, but rather by some other factor not yet apparent. 



One has but to compare the 11 -year average with that for any one of the individual years 

 to raise the question as to the degree of importance to be assigned to studies covering short 

 periods. The bulk of many of the foods taken in any of the 11 years here compared shows 

 wide variations from the 11-year average. Deviations too large to be ignored are likely to be 

 obtained by drawing conclusions on the volumes taken over short periods, unless one is in- 

 terested primarily in obtaining a mere list of foods and a rough indication of the extent to 

 which they are utilized. The degree of reliance that one may place on such generalities is indi- 

 cated by the fact that, of the five genera taken in greatest volume over an 11-year period, in 

 only four years were the same five at the head of the list, and even then the order was shifted 

 in each case. In 1934, 1935 and again in 1939 but three of the group were among the first 

 five. 



