States. Major fluctuations in the frequency of muskrat trapping pre- 
sumably affect the number of banding recoveries, but I did not attemot 
to detect them in the small sample available for study. 
The breakdown for a sample of 92 mallards banded through the 
spring of 1937 is illustrated in table 30. Eighty-nine of these had 
a mean annual mortality of 50 per cent from age x + 1 to age x + 7 
inclusive, the data for subsequent age intervals being slightly in- 
complete. The survival curve is fairly straight on semilog paper for 
6 or 7 years. A possible increase in survival rate in the later years 
of a mallard's life (when vulnerability to predation and hunting q 
possibility decreases with added experience) is studied in Chapter XIV. 
s 
Table 30.—-Banded Mallards Reported Caught In Mammal Traps 
These birds were unaged at the time of banding (August to April 
inclusive). Each year starts as of June 1, but all birds re- 
covered in the same year in which they were banded (age interval 
x) are omitted. Brackets and the symbol X signify age intervals 
That were not included in the totals and means at the bottom of 
the table because the data for these ages were incomplete or 
unavailable when this table was compiled. 
When Banded my. Woeessy. if ne Ge Pant eS es 
177) a [Sr 
Age Interval ane —_ Caught Calculated 
in Years in Traps Mortality in Traps Mortality 
x+ltox+ 2 14,6 28 89 Sh 
x+2 tox +3 18 OH 35 15 
x+3tox+ 11 L 20 5 
x+htox4+5 7 3 15 x 
x+5 tox +6 k 2 x x 
x+6tox+7 2 1 x x 
x+7tox+ 8 1 -1 x Xx 
x+8toxs+9 2 (1) x Xx 
x+9toxe1 1 ( X X 
, 0 by 1) 
~—_fotalL 
Mean Mortality Rate 
(per cent per year) 50 
| 

y excludes last 2 age intervals 
2/ for first 3 age intervals only 
A second sample, banded up through the spring of 191, greatly 
increases the amount of recoveriss available for age groups and gives 
a 3-year mean mortality rate of 51 per cent. 
Age ratios and productivity 
From our short review of the nesting biology of the North 
American mallard, it is evident that no precise analysis of average 
71 
