As one progresses down river, peak dates are delayed 
approximately 1 week for each unit of Mark Twain Refuge. For 
example, Louisa Unit recorded its earliest peak during the week 
ending November 2, its latest during the week ending December 7, 
and averaged about the week ending November 23. Calhoun Unit 
(the southermmost, located at the mouth of the Illinois River, 
and about 250 miles south of the Upper Mississippi Refuge) had 
its earliest peak during the week ending November 30, the latest 
during the week ending December 28, and averaged the week ending 
December 7. 
The earliest opening day during the period of this study 
was October 1. By referring to table 4, it will be noted that 
by opening day there have been fair populations of ducks present 
on most refuge areas, except at Louisa, Keithsburg, and Gardner 
Units of Mark Twain. 
Table 4 - Opening Day Populations 
Minimum Maximum Average 
Opening Day Opening Day Opening Day 
Refuge Count Count — Count 
Upper Mississippi 56,092 (10/1/53) 136,455 (10/1/58) 94,2 
Louisa 225 (10/6/56) 16,862 (10/20/59) eet 
Keithsburg 100 (10/19/57) 1,281 (10/28/60) 710 
Gardner * 125 (10/18/58) 2,322 (10/30/59) 1,540 
Batchtown 500 (10/22/54) 156,450 (10/28/60) 31,150 
Calhoun 13,350 (10/15/55) 35,000 (10/13/56) 27,305 
* Only 3 years' data 
Tables 5 through 9 show a comparison of peak dates, peak 
numbers, and average peak populations for the area under consid- 
eration. 
Duck-day use 
The two refuges support heavy duck-day use. Tables 10 through 
1h indicate that an average of 38,025,391 days of duck use occurs 
each fall. The Upper Mississippi Refuge has an average of 
10,879,065 days' use; while the units of Mark Twain Refuge have a 
combined average of 27,146,326 days' use. Much of the use on Mark 
Twain occurs late in the fall, but with delayed hunting seasons 
there is still heavy use during the open season. On the Upper | 
Mississippi Refuge it was found that over 84% of all fall duck use 
occurred during the period of the open hunting season, while for 
the entire area nearly 82% of all fall use occurred during the open 
season. Furthermore, the average weekly duck population occurring 
11 
