. Bulletin. Natural history; Natural history. 446 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Horicon Marsh in Wisconsin, the Pointe Alouillee Marsh in Michigan, the marshes at Sandusky Bay in Ohio—show h'ttle cor- relation with changes in the Mississippi River basin areas, fig. 16. However, the Great Lakes areas are frequented by only a small proportion of the mallard popula- tion of the Mississippi Flyway; these areas are to the east of the principal routes used by mallards migrating between their breeding and wintering areas. I'here was reasonably close agreement in the year-to
. Bulletin. Natural history; Natural history. 446 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Horicon Marsh in Wisconsin, the Pointe Alouillee Marsh in Michigan, the marshes at Sandusky Bay in Ohio—show h'ttle cor- relation with changes in the Mississippi River basin areas, fig. 16. However, the Great Lakes areas are frequented by only a small proportion of the mallard popula- tion of the Mississippi Flyway; these areas are to the east of the principal routes used by mallards migrating between their breeding and wintering areas. I'here was reasonably close agreement in the year-to-year fluctuations in the num- ber of juvenile mallards per adult in hunt- ers' bags in the Mississippi River basin areas: the Upper Mississippi River, the Illinois River valley, and the Stuttgart, Arkansas, area, table 51 and fig. 16. There was a highly significant relationship be- tween the age ratios of mallards bagged in the Upper Mississippi River area, Illinois River valley, Missouri, and Arkansas dur- ing the period 1946-1949, table 51, as demonstrated by a correlation coefficient of r=+ or higher, which indicated that the probability that the correlation was due to chance was less than The age ratios for mallards bagged in the Illinois River valley were close to those for mallards taken in the Stuttgart, Arkansas, area in all but 2 (1950 and 1953) of 11 years (1946-1955 and 1959), table 52 and fig. 16. The lack of agree- ment in the age ratios from the two areas in 1950 and 1953 is believed to have been related to a delayed hatch on the breeding grounds followed by a somewhat delayed movement of juveniles to Illinois, where a high kill of these young birds occurred. In 1950, mild weather induced large numbers of mallards to remain on the breeding grounds until November 7, when a severe cold front resulted in an unusu- ally large exodus. The ducks moved rap- idly down the flyway, and the adults passed through Illinois without stopping so long as is customary
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