per cent, indicating that about half of the number of birds shot would have died before spring 
from natural causes, if the areas had not been opened to hunting. 
In the 1939-1947 period, the natural loss in the mallard population migrating through 
Illinois was so small that any marked increase in the kill would undoubtedly have resulted in a 
proportionate rise in the total mortality. The natural loss had contracted to the point where a 
stretching of the hunting loss might have had disastrous results. 
If this line of reasoning is valid, the blue-winged teal and perhaps the black duck 
could undergo greater hunting losses without raising their total mortality rates. In this con- 
nection, it is necessary to consider that the potential stretch and contraction, or ''give and 
take,'' between natural mortality and shooting mortality differs in various species of ducks, 
Several wild game species are known to possess a flexible productivity potential of 
such a nature that they respond to increased mortality with an increase in productivity. 
Bump et al. (1947) found that, although hunting increased the mortality rate of 
ruffed grouse, the flexibility of the productivity potential tended to overcome this added loss. 
They found from a correlation of population data between protected and hunted populations that 
there was a distinct tendency for greater relative increases of young to be associated with lower 
breeding populations; thus, there was an inverse relationship between the number of grouse in 
the spring and the proportion of juveniles in the fall population. This population phenomenon has 
also been demonstrated by Errington (1945) to occur in bobwhites and by Allen (1943) in fox 
squirrels. Its wide occurrence in small game populations would lead us to suspect that it is 
present also in waterfowl populations. 
To what extent the flexibility of the mallard's productivity potential could overcome 
increased mortality in Mississippi flyway populations is at present conjectural. 
The mallard has a high reproductive potential and appears to be capable of maintain- 
ing its population under conditions of at least moderately high mortality losses. On the other 
hand, its breeding potential: in the north may be affected by drastic annual fluctuations in breed- 
ing habitat, and in certain years, despite the excellent reproductive potential of this species, 
total numbers may be affected by the area available for expression of this potential. 
This paper only opens the door to the subject of population losses in waterfowl. Even 
where the conclusions appear final, they may be only temporarily so. Future, more extensive 
studies may reveal, for example, that hunters report more or fewer bands, or that the loss 
from crippling is greater or less, 
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