
With scaup, on the other hand, the low harvest in propor- 
tion to the population, probably reflects more the type of hunt- 
ing than vulnerability, since most of the hunting along the river 
in the areas checked is done from blinds and in the marshes 
rather than on open river "points." The same holds true for 
canvasbacks which comprise 2.50% of fall use on the Upper Missis- 
sippi but only 0.93% of the checked kill; while for the entire 
area, this species makes up 1.03% of total use and 0.50% of the 
checked kill. 
Tables 21 and 22 compare the species camposition in the fall 
flight with the species composition in the checked kill, together 
with the number of years for each category from which data are 
available. All figures shown in these tables are average figures 
based on length of time the data cover. 
Comparative vulnerability of species 
Since duck species were represented in different abundance 
in the population and in the harvest, there is probably a differ- 
ence in vulnerability to gunning. Vulnerability, as considered 
here, encompasses all facets of the harvest and recognizes that 
there is a difference in the way in which the various species are 
taken. Whether this depends on being more vulnerable to the gun, 
& preference by hunters, weather conditions, response to decoys, 
or the type of hunting done is of little consequence. The impor- 
tant thing is that for a given segment of the population present, 
some birds are taken in a higher ratio than are others. Vulner- 
ability, thus, relates entirely to the ratio of harvest per unit 
of population, regardless of why these different ratios apply. 
In comparing the data, it became apparent that within rather 
close limits, mallards were present in about the same relative 
abundance in both the population and the harvest. They accounted 
for 37.60% of the population and 40.30% of the checked kill. Since 
these figures were so close, it was decided to arbitrarily assign 
&@ vulnerability rating of 1 to mallards and to compare all other 
species to them. 
Using the above percentages for mallards (37.60% in the 
population - 40.30% in the checked kill) as a base, the mallard 
index was obtained by dividing the percentage of the checked kill 
by the percentage in the population which gave an index of 1.07 
for mallards. This was then arbitrarily set up as a vulnerability 
rating of l. 
For black ducks, it was found that they accounted for 1.91% 
of the population on the Upper Mississippi Refuge and 2.28% of 
the checked kill. Dividing as before, an index of 1.19 was obtained. 
To correct this on the seme basis as for mallards, the following 
formula was used: 
34 
