1939 1940 1941 1942' 1943 1944 1945 1946 
-40 —41 -~42 —~43 ~44 —45 —46 —47 

NO. OF DAYS 
US. HUNTING 
S ADULT 
SURVIVAL INDEX 
30 Isr SEASON RECOVERY RATE 
DU (CANADA) 
COOK CO..ILL. 
Figure 20.--Associations of Survival of Adult Mississippi 
Valley Mallards in the 19l0's 
Annual survival rates (starting as Sept. 1) are here approximated by 
a survival index (described in Chapter III). The percentage of 
juveniles among mallards shot by hunters was obtained in the Illinois 
River Valley by personnel of the Illinois State Natural History Survey 
(Hawkins, in litt.). First-season recovery rates are for unaged mal- 
lards (from figure 14). Interpretation: No general relation of 
adult survival rate and length of hunting season in the United States 
during this period is evident. Because the period began when the 
population was thought to be high, the lack of association between 
adult survival and annual production of young is to be expected 
during the years 1939-40 and 1940-41. The gradually increasing 
association of these two statistics could be explained as a chance 
phenomenon or as the result of a population declir? in which the pro- 
portion of juveniles in the population became more and more important.- 
152 
