Chapter XIII.--Variations in Mallard Mlortality Rates oa 
In Chapter VI, it was shown that 1230 adult mallards banded 
in the Mississippi Valley from 1922 to 1926 had a mean annual mor- 
tality rate of 6.5 per cent per year, while 1762 adult males banded — 
on the Pacific coast from 1926 to 1935 had a mean average of 8.5. 
That this conformity is the result of averaging a wide variety of 
conditions can be seen in table 57, which brings out a significant , 
difference between rates calculated for Pacific coast adults banded 
in 1926-30 and those banded in the nest 5-year period. This con~’ 
vircing difference could mean that important differences in annual 
mortality rates occurred from one year to another, or that the _ 
heterogeneous collection of reports from different places on the 
Pacific seaboard contained regional differences that showed up in 
this fashion. 
Variations Between the Sexes 
Variation in mortality rates between the sexes was explored 
only at the start of the study. Time-specific estimates on birds 
banded in Oklahoma by H. S. Davis and R. H. Jordan permitted means 
to be calculated for the first 3 age intervals subsequent to banding. 
These are included in table 58 along with four other dynamic life- 
table computations derived from materials in the U. S. banding files 
and a fifth set recalculated from the literature. 
Tt would appear from the few samples in this table that 
rather striking mortality-rate differences exist either geographically 
or chronologically for this species, and that two patterns involving 
different mortality rates for the two sexes are possible. Bellrose 
and Chase (1950) rightly ascribe the hizher mortality rate in their 
sample to the probable vulnerability of females to predators during 
the nesting season. One naturally wonders if the higher mortality 
rates for males in the facific Flyway represent a greater selectivity 
of hunters shooting males in preference to females. This problem 
may be studied in table 59 which I compiled at the ‘suggestion of 
A. S. Hawkins. 
The differences in first-season recovery rates reported 
here (1.4 and 1.6 per cent) closely follow those evident in Bell- 
rose and Chase's (1950) study of mallards banded at Lake Chautauqua 
Illinois: 6.3 per cent for 22,28 males and 5.0 per cent for 8628 
females. These differences also increase in a similar manner as 
more years are added to the recovery periods. There is thus no 
evidence presented here that demonstrates any difference in hunter 
selectivity on the west coast and in the Mississippi Valley. We 
are left with the implication that nesting conditions encountered | 
by the Pacific Coast birds reviewed here possibly differed from 
those postulated for the Illinois-banded birds studied by Bellrose 
and Chase (1950). 
136 
