Hourly-success data 
Again, these data were obtained from voluntary reports of 
hunters checked as to how long they were afield on the day they 
were checked. 
Hunting pressure 
Each week during the hunting season the district managers 
on the Upper Mississippi Refuge report the total man-days of hunt- 
ing in the districts. These reports are based on car counts, 
concentrations of hunters, number of hunters contacted in the 
field, etc. District reports are combined into an overall refuge 
report. Since these data are collected the same way every year, 
there is a good basis for comparing hunting pressure from year to 
year. 
On Mark Twain Refuge hunter-use data are obtained by indi- 
vidual units and are based on car counts, hunter contacts, and 
records of hunters passing through the check stations operated 
by Illinois and Iowa. 
Estimation of total kill 
Estimated total kill is calculated as follows: For each 
district on the Upper Mississippi Refuge, the average daily bag 
for the season and the average daily crippling loss is based on 
the sample of the hunters actually checked. These average 
figures are expanded to derive the estimated total kill. Thus, 
if the average daily kill is determined to be 1.30 ducks and the 
total hunting pressure estimated at 20,000 man-days, it is assumed 
that all 20,000 hunters succeeded in taking the average harvest, 
and an estimated bag of 26,000 ducks is calculated. If the aver- 
age crippling loss is 0.25 ducks per hunter per day, this figure 
is~similarly expanded to show a crippling loss of 5,000 ducks. 
fhe two figures are then combined to indicate an estimated total 
kill of 31,000 ducks for the district. After these data are 
worked up for each district, the district totals are added to 
arrive at the refuge total. 
On Mark Twain Refuge a similar system is used, expanding the 
seasonal average of daily kill and crippling loss from each Unit 
by multiplying the seasonal averages by estimated total days of 
hunting. Data from each Unit are combined to give the total refuge 
figure. 
Where kill data are shown for the entire area, they are a 
composite of information from both the Upper Mississippi and Mark 
Twain Refuges, each of which was separately computed as described 
above. 
