PRODUCTIVITY OF POPULATIONS 



527 



during this period by the occurrence of infertile eggs and embryos which do not survive in 

 clutches the remainder of which hatch successfully. These have been of minor importance 

 in the experience of the Investigation.* So also have been the eggs now and then filched 

 by foxes and other predators. 



•ABLE 80. 



PROPORTION OF BROKEN-UP GROUSE NESTS OBSERVED DURING THE 

 INVESTIGATION ATTRIBUTED TO VARIOUS CAUSE.S— 1930-1942 



* A greater number of broken-op nesls were observed then 

 were comparable for correlation with the number known 

 to have hatrhr<l as shown in table 35. 



Except for the occasional "drowning" of a nest, weather has had no recognizable effect on 

 nesting success, although certain conditions may facilitate discovery by predators. 



Brood Period 



By late August, broods comprising more than a hen and four chicks have been uncommon 

 and those with fewer chicks frequent. Average survival, however, has varied appreciably 

 between years (table 81), although the mean for the period covered on both the Connecticut 

 Hill and Adirondack study areas has averaged slightly less than 40 per cent. 



TABLE 81. BROOD SURVIVAL RECORDED ON CONNECTICUT HILL AND ADIRONDACK 



STUDY AREAS— 1930-1942 



*These figures in some cases are larger than those given elsewhere with resfiect to population trends becatise survival data were 

 often secured on broods occupying territory adjoining the area proper. 



It has also shown a strong similarity in trend in the two localities. This is especially note- 

 worthy in view of the distance between them and the fact that the general abundance of grouse 

 on the two has been very different. Furthermore, adjustment of the data for each area by 

 analysis of covariance for differences in the number of chicks hatched each year indicates 



• See Chapter Vlll. p. 365. 



