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Vo 1. 25, Ho. 1 
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fall peak. Mallards constituted 90S; of the peak in 1901, compared with 80% for 
the 137G-1980 average peak. The slightly higher proportion of mallards in 1981 
is probably a result of the late population buildup. Fall migration numbers 
usually peak around the third week of November in the Illinois Valley when more 
of the early migrants such as teal, pintail, wigeon, and aadwall are present. 
Duck numbers reached an early peak of 8 / 47 ,000 birds on 26 October 1 98 1 in 
the central Mississippi Valley (Grafton to Rock Island). This concentration, 
comprised primarily of diving ducks, was slightly lower than the peak of 9^3,000 
on 3 November 1 980 and considerably lower than the 1973-1980 average fall peak 
of 1.^4 million birds. Peak mallard numbers (3^2,000 on 23 November 1981) were 
also down in the Mississippi Valley from the 1978-1930 average peak of 656,000. 
Locations most used by ducks changed little in l931 from previous years. 
Goose Pond (Bureau County), Hitchcock Slough, Grand and Cuba islands, and 
Senachwine, Peoria, Powerton, Dig, Chautauqua, Crane, Meredosia, Flat, and Swan 
lakes hosted the most ducks in the Illinois Valley. In the central Mississippi 
Valley, ducks preferred the Keokuk Pool, water areas in St. Charles County, 
Missouri, and Oqwawka, Keithsburg, Louisa, Batchtown, Cannon, Delair, and 
Shanks refuges. 
The decrease in the 1931 duck populations in the Illinois and Mississippi 
^ valleys was expected by duck hunters and biologists. Another poor hatch of 
young on the breeding grounds combined with poor food resources resulting from 
the high water conditions of summer (Ml/RL 2^(11):4) are major factors 
responsible for the decline. 
