An abridged dynamic life table for 71 redheads (table 33, 
part A) indicates that the life span was short for most of the popula~ 
tion (less than 5 full years for 99 per cent of the birds sampled) 
and that the adult mortality rate was of the order of 5 per cent. 
In an effort to confirm this adult rate, a time-specific life table 
(table 33, part B) was also constructed, using banding work up to 
1942. The small number of adult recoveries encountered was disap~ 
pointing, but a reasonably close approximation of the same rate 
was obtained. The juvenile mortality rates derived here will be 
examined under Age Ratios and Productivity. 
Age ratios and productivity 
The preponderance of juvenile birds (87 per cent) in 
table 33, part A, is identical to that to that found by Williams 
(194) in an analysis of 357 recoveries of Utah-banded birds. The 
data would at first seem indicative of band loss in the adults, 
but Hochbaum (19));) has shown that 92 per cent of 277 redheads 
bagged at Delta, Manitoba, were first-year birds. The banding 
data thus reflect a condition found in the field and are not biased 
by a loss of bands among the older birds. 
If we consider the age ratio among the birds alive in 
table 33, part A, we obtain a value of 4.2 juveniles per adult as 
of September 1, equivalent to 8.) young per pair. J. B. Low (195) 
found that the average at hatching in Iowa was 4.) young per pair, 
and I conclude from his paper that the age ratio in Iowa is of the 
order of 1.5 to 1.8 young per adult at the start of migration. This 
discrepancy between the life-table population and a natural popula~ 
tion arises here from the violation of a basic assumption in life- 
table compilation: that the birds reported as dying in each age 
interval are typical of the unreported or unrecovered birds dying 
in similar age intervals. There is a strong probability that after 
the close of the hunting season first-year birds die from natural 
causes at approximately the same rate as adult birds. Now, if — 
the juveniles are, say, twice as wilnerable to hunting as adults 
are and if hunting reports form the sole basis for the life table, 
the life table would not be typical of mortality occurring after 
the hunting season. First-year mortality rates would then be 
exaggerated. This type of exaggeration has been illustrated in 
table 13 in Chapter III. It is frequently encountered in sur- 
vival analyses based on birds shot, but it does net imply that 
the mortality rates for adults calculated from such data are wrong. 
Population dynamics 
The somewhat precarious status of the redhead on the North 
American continent should encourage us to obtain a picture of its 
population turnover as soon as possible. Two important statistics 
need to be carefully ascertained before this can be done with relia- 
bility: (1) an accurate field appraisal of the average ratio of | 
juveniles to adults in the population at the start of the hunting 
76 
