PRODUCTIVITY OF POPULATIONS 



539 



Net Productivity 



The degree of survival observed during each life period from year to year has been dis- 

 cussed. Yet the actual number of grouse which a hunter may find in a covert in the fall 

 depends on the net success of the whole breeding and rearing season. Likewise the size of 

 succeeding breeding populations rests on the progressive survival throughout the year. The 

 records of the Investigation for the areas studied afford some idea of how this net produc- 

 tivity may vary. 



Considering first the hunting season, table 87 presents the ratio of the April to the Septem- 

 ber* populations observed on the two principal study areas. 



TABLE 87. 



PRODUCTION RATIO OF GROUSE BREEDING POPULATIONS ON 



CONNECTICUT HILL AND ADIRONDACK STUDY AREAS 



AS OF SEPTEMBER 1—1930-1942 



* Figures in parenthesis computed frum number of adults remaining in September on basis of average summer lossea for pre- 

 ceding years since no spring census was made on this area after 1938. 



On both a considerable range of productivity has been observed. In one instance on each 

 area, 1933 on Connecticut Hill and 1935 on the northern tract, the populations barely held 

 their own. On other occasions they more than doubled themselves. In fact, on the Adiron- 

 dack area the ratio twice reached 3.04, ahhough in 1934 the proportion was actually a little 

 lower since several birds were known to have moved in from surrounding territory during the 

 summer. On the basis of this record anything over 2.0 may be considered to represent a 

 good crop. 



The reasons for low productivity have been different on different occasions. In 1933 on 

 Connecticut Hill unusually high losses throughout the breeding, nesting and rearing periods 

 resulted in a net decrease by September. In 1935 on the same area, in spite of a low nest 

 mortality, what the authors believe to have been a high degree of breeding failure^ coupled 

 with low brood survival, resulted in an increase of only 1.17. In 1940 nest mortality alone 

 was controlling, and in 1942 brood mortality. On the Adirondack area very high brood losses 

 were responsible for the poor crops in 1933 and 1935. 



Of interest is the fact that the lower densities characteristic of the latter area have exhibited 

 a somewhat higher average production ratio. Beyond this, correlation of the data for each 



"'■* No iDdication haa been nnted of more than very minor mortality between September and the usual open season. 

 A See Chapter VIII, p. 359. 



