CHARACTERISTICS 567 



in each case has been that during the fall of which the grouse population first reached a sig- 

 nificantly low level even though the absolute bottom of the trough may have been a year or 

 two later. Not only is it often difficult to determine which season was lowest but the year in 

 which scarcity was first reached must have been more closely associated with the conditions 

 which were responsible. 



The second index is that of the last year of real abundance preceding each major decline in 

 each region. Here, too, the year plotted is not necessarily the one during which the fall grouse 

 population was at its maximum. Rather it marks the end of each period of generally high 

 abundance and, in conjunction with the year when the following low ebb was reached, further 

 delineates the primary interval of decline. 



It is evident from this chart that the major declines in grouse abundance during the years 

 covered have not taken place simultaneously over its range. Records indicate that the nearest 

 approach to uniformity probably occurred in 1907. although in 1917 also grouse ])opulations 

 over a large proportion of this range were reported to have reached a low level at the same 

 time. But in the latter instance there was wide variation in the year when the decline com- 

 menced. Since then the pattern has been more irregular, exhibiting the greatest degree of 

 variability during the decade between 1920 and 1930, when, paradoxically, the initial year of 

 decline seems to have been quite uniform. 



Even closely allied regions such as Minnesota and Wisconsin have not usually been affected 

 simultaneously. Yet considerable similarity is shown in the records for Minnesota, Michigan 

 and northwestern and central Ontario. In New York the declines of 1907 and 1917 coincided 

 with similar fluctuations in Pennsylvania and New England, but subsequent years have shown 

 a lack of harmony in this territory. Apparently the populations of various regions tend to 

 react independently of one another. 



Similar conclusions have been stated regarding the population behavior of other species. 

 MacLulich''" after intensive study of the snowshoe hare in Ontario demonstrated that '"the 

 last year of great abundance, which is the year in which the decrease began" varied from 

 1932 to 1935 ill different districts. Likewise Cross"' after studying the red fox iVulpes julva) 

 in Ontario found, with respect to different regions of the province, tliat "there were wide 

 variations as to the years in which the maximum numbers occurred, the years in which the 

 minimum numbers occurred and in the intervals between these years". 



On the other hand, it has been suggested that the onset of grouse scarcity, while not at any 

 time sinniltaneous over the range, might nevertheless follow a similar course from region to 

 region in recurrent instances. The records are conflicting in this respect, however. Clarke's 

 data for Canada in the '30s'' exhibit a trend begiiming in the northeastern and northwestern 

 districts at about the same time and progressively converging southwestward and southeast- 

 ward respectively. A pattern of this kind during that decade is further indicated by the fact 

 that conditions in Maine and the Lake States roughly coincided with those of Quebec and 

 Ontario while the decline in New York. Pennsylvania and southern New England took place 

 still later. Figure 59 also indicates that the pattern was generally similar in the previous 

 decade. But no such progression is apparent in the records prior to 1920. Neither does it 

 seem to be true of the current situation although this has not yet run its course. In this con- 

 nection it may be mentioned that in Nova Scotia the recent period of grouse abundance seems 

 to have ended earlier than elsewhere even though this was not similarly true of the time 

 when the population reached a significantly low level. Thus the available evidence does not 

 support the idea that recurrent declines follow a regular sequence between regions. Yet in 



