. Bulletin. Natural history; Natural history. 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 Fig. 12.—Year-to-year variations in the seasonal migration of juvenile mallards through the Illinois River valley, 1939-1950, as shown by the proportion of each year's juvenile flight that was in the valley in each of 6 weeks in autumn. 60) and in 1953 (Lynch & Gollop 1954: 47; Gollop 1954:67; Hawkins 1954:77). That the age composition of the mal- lard population in Illinois varied from week to week in the fall is shown by checks of hunters' bags, table 44. In any one year, pronounced
. Bulletin. Natural history; Natural history. 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 Fig. 12.—Year-to-year variations in the seasonal migration of juvenile mallards through the Illinois River valley, 1939-1950, as shown by the proportion of each year's juvenile flight that was in the valley in each of 6 weeks in autumn. 60) and in 1953 (Lynch & Gollop 1954: 47; Gollop 1954:67; Hawkins 1954:77). That the age composition of the mal- lard population in Illinois varied from week to week in the fall is shown by checks of hunters' bags, table 44. In any one year, pronounced week-to-week vari- ations in the age composition of mallards taken by hunters in Illinois suggest that there may be many migratory movements, some scarcely detectable, within a local population. The adult-juvenile composition of the mallard flight in Illinois for the period 1939-1949 is reflected in fig. 13. Gen- erally, juveniles made up a greater part of the mallard bag early in the season than later. The juvenile proportion in hunters' bags soon declined, as indicated by data collected during the first half of Novem- ber; it recovered somewhat during the second half of November but declined again during the first 2 weeks of Decem- ber. The decline in December resulted as juveniles moved farther south and large numbers of adults moved into Illinois from the north. In 6 of 7 years, juvenile mallards in Arkansas formed a greater proportion of the hunters' bags in the second than in the first of two periods during which data were collected, table 49. The findings shown in fig. 13 and tables 49 and 50 suggest that, between the mid-flyway areas (Illinois) and the wintering grounds (Arkansas), juveniles may be more prone to leisurely migration than adults. The daily change in age composition of the mallard bag at Stuttgart, Arkansas, for December 2-11, 1950, is given in ta- ble 50. A marked change in the relative number of juveniles in the bag occurred on December 8. A large sout
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