528 



PRODUCTIl IT) OF GROUSE POPULATIONS 



that variations in the net effect of the forces responsible have paralleled each other quite 

 closely (figure 43). 



TO 



I 

 I 

 I 



Connecticut Hill 



Adirondack 



I 



J l_ 



-I L 



TO 

 •40 

 lo 



I9S0 1931 193Z 1933 193>4 1935 1934 1937 1938 1939 1940 1941 I94Z 



YEAR 



FIGURE 43. GROUSE BROOD SURVIVAL RECORDED ON CONNECTICUT HILL AND ADIRONDACK AREAS 



—1930-1942 



The primary causes of losses at this age, however, are still a major problem. Predation 

 seems to be responsible for rouphlv half the mortality in averajie seasons. Few specific data 

 have been obtained to account for the remaintier. As noted in Chapter VII (p. 316), a sub- 

 stantial parallel has been observed between the early decline among grouse chicks hatched 

 and reared artificially at the Research Center and that among wild broods. But even here the 

 closest diagnosis which has been possible so far is the ambiguous term ''nutritional defi- 

 ciency" which seems actually to refer to some physiological disturbance as sufficient food 

 is always available to these birds. Also studies of the foods eaten by wild chicks have indi- 

 cated a superabundance. Another influence is weather but its significance has not been de- 

 termined, although there can be little doubt that the cloudburst in central New York in early 

 July. 1935, directly increased the mortality of grouse chicks. Furthermore it seems most 

 likely that the markedly lower survival experienced in some years may fundamentally be the 

 result of some combination of these other factors rather than of predation. There is no evi- 

 dence, however, that disease has been important. 



Among the relatively few chicks found dead on the study areas, no cause of death other 

 than predation has been noU'd. althougii in 21.7 per cent of the cases no diagnosis at all could 

 be made. Elsewhere fatalities resulting from highway and miscellaneous accidents have now 

 and then been observed. 



It has been suggested that, as the number of chicks hatched |>cr unit of area decreases, the 

 corresponding proportion maturing tends to increase. Ihc data, howcycr, do not support such 

 a conclusion as shown in table 82, in which the records for the Connecticut Hill and Adiron- 

 dack areas were grou])ed according to the relative alunidance of chicks at the beginning of 

 the brood period. In fact on the northern tract, better survival was associated with the higher 



