productivity per adult is possible at this time. Allowing for 10 per 
cent adult mortality during the nesting season and renesting by 50 
per cent of the females that lose their first clutches, reproduction 
would appear to result in an age ratio of the order of 3 juveniles 
per adult at the time of banding. Even with considerable juvenile 
mortality between the flapper or banding stage and the peak of the 
hunting season, this productivity would be ample to stabilize the 
population implied in tables 28, 29, and 30. First-year mortality 
rates of 68 or 73 per cent as of September 1 are thus possible, but 
being derived from small samples they must await further verification. 
Discussion of the dynamics of mallard populations is deferred until 
‘Part III, where variations in mallard mortality rate are given in 
greater detail. 
Summary 
The literature on North American mallards reveals that the 
mean clutch for 541 nests observed was 7.8 eggs, that the mean number 
of young in 1310 broods was 7.1, and that the shrinkage in brood size 
for 758 broods in Minnesota was about 20 per cent from hatching to 
the time the young were ready to fly. The number of unproductive or 
unsuccessful females in the population is still unknom, but 55 to 
70 per cent of all nests studied have hatched. 
Preliminary calculations of first-year mortality rates for 
a small sample of 163 wild-reared juveniles yielded 68 per cent, the 
bias in this figure being difficult to assess. A mean adult mortality 
rate of 47.8 per cent for 2992 birds unaged at the time of banding 
checked fairly well with a smaller sample of birds of known age. 
Birds captured in mammal traps had the same overall mortality rate 
as those reported by hunters. Hand-reared birds had a considerably 
higher initial mortality rate than wild-reared ones, the difference 
possibly persisting until the third year of life. The mortality 
rates found here for Nort: American birds were considerably lower 
than those reported for mallards in Great Britain. 
72 
