516 



PRODUCTIVITY OF GROUSE POPULATIONS 



It would thus appear that the sex ratio among adults at the end of the summer, in which 

 females predominated, shifted to one having a majority of males between that time and early 

 winter. Further, the fact that there has been no indication of hens suffering heavier decima- 

 tion during the fall than cocks suggests that males outnumbered females among the maturing 

 birds of the year. 



Analysis of collections of young grouse from .August through December since 1938* 

 further indicates this possibility (table 7.5). It is recognized that these data are subject to 

 sampling errors through selective shooting as noted above, although to a lesser degree because 

 similarity in the habits of birds of this age is probably greater than among older birds. Never- 

 theless the differences are sufficientlv consistent to be noteworlhv and statistically sound as 

 demonstrated by analysis of variance. But the reasons for unbalanced sex ratios among matur- 

 ing grouse are still obscure. 



•|\HLI'; 7.-). SE.\ It.vnOS OF IMMATURE GROUSE— STATEWIDE COLLECTIONS- 

 AUGUST 1 THROUGH DECEMBER 31—1938-1941 



If the trend so far suggested is real, then some influence must bring about another shift in 

 the sex ratio from more males in winter to more females in summer. Such a factor seems to 

 be a differential mortality in spring through which the cocks suffer more heavily. Of the 477 

 dead grouse (which were sexable) found on the Connecticut Hill area throughout the Inves- 

 tigation and judged to have died from January through May. 59. .5 per cent were males. That 

 this is quite likely associated with the breeding behavior of the cocks, especially drumming, 

 is indicated by the fact that their mortality cui vc reaclii-^ it.- |ieak in \iiril while that of their 

 mates drops off following a high in March". 



These data, therefore, indicate the existence of a basic tenileni\ fur llic sex ratio of wild 

 grouse populations to become unbalanced in the spring through a disproportionate mortality 

 among males, following which the balance is swung the other way by a jireponderance of this 

 sex among the maturing young in the fall. Normally the ratio is most nearly even at some 

 time in late winter or early s()ring. . 



It is likely, however, that this fundamental pattern is often modified by various circum- 

 stances. For example, in a season of failure in the chick crop, the mitnber of maturing males 

 might not be sufTicient to offset the summer surplus of females. Then the ultimate effect would 

 be an augmented proportion of breeding females the following spring lending to compensate 

 for the previous year's low priiduitivil\ . On the other hand, the greater the proportion of 

 maturing young in tin- f;ill. ;in(l bcjuc llic number uf <'\lia males added, the more the 

 resultant ratio would favor that sex. 



That such changes arc often associated with nuctualions in produclix il\ llicrc ran be little 

 doubt, but it has been impossible from the data at hand to determine just how strong the 



* Thr l>iir*t n( Fabrirtis an a rriirrirtn of agr M.ifi imr knoun to the Invptiigatioii prinr to 1938, 

 A Sri- itUcunaiiin nf ,A<lllIt Survival. |>. .S16. 



