"Table 69.--Some Age Ratios in North American aes 
Real ang cine 


~B: *: ome oe Qw-=+- = 
Source of. Data Piste =c=— «Life “Table -=-+---! ‘Hunters! Bags — ! 
Time. Implie’t | Sept. 1. (Late Fall): ‘Feb. - Early Fall Late Fall 
Period Studied: 1925-h6 1939-7 19h0-7 192h-hé 1939-42 195-49 


Where Secured § No. Am. Tll,. Ill. No. An.- Man. -Ark.. 
Size. of Sarple 163 pak 2257 4377 1270 ++ 
093 var 
aiias Per Adult 1.6 ~76-.88 0.91 0.95 202 1.45% 
Per Cent: Youn 61. h3-h7# 47.6 48.7 69.5 59.2 
Reference. . - Fabis Bellrose and Table Hochbaum Hawkins 
feetin a 28 Chase (1950) 67 (1944) - (in litt.) 

* arithmatic mean of ratios for 5 separate years 
# recalculated as per table 58 
Using colum (3) + (4) in table 68 as a very rough sort of 
putida, we can now examine in table 69 the age ratio of 2.2 young per 
adult. reported from Manitoba hunters! bags by Hochbaum (194). This 
ratio would seem to suggest either less-than-averazge production in 
1939-l1.or differential migration by the young birds. The ratio of 
1.45 young per adult found by Hawkins (table 69) in Arkansas would 
appear to demonstrate better-than-average production in 195-9. 
Annual adult mortality rates.-~As I have pointed out in 
the discussion of table 61, no reliable method for measuring mortality 
rates for. specific years emerged in this study. That these rates 
do vary widely from one year to another cannot be doubted. In table 70, 
TI have gathered together some mortality "rates" based on a series of 
cohorts (birds banded in separate years). These approximations of 
what is occurring in mallard populations seem to suggest that at 
least during this period mortality in this species was by no means 
a local phenomenon. They are also a clear warning that comparative . 
mortality rates for two species of waterfowl are most reliable when 
based upon birds banded during the same period. 
‘Table 70.--Comparison of Adult Mortality "Rates" for 
Different Regions 
Data from materials in Chapter media lee Each year starts as of 
September le 
Mortality Rates Calculated for Specific Years 
Where banded 
Montana té). S(t 63) C6 Ca 
Illinois...) | eee tet et | ere eae giao 3 
161 
