. Bulletin. Natural history; Natural history. 452 Illinois Natural History Survlv Bulletin Vol. 27, Art. b principally Illinois. It is apparent that the ratio of adult to juvenile vulnerability has no correlation with the number of juveniles per adult baj:;^ed by hunters. Table 58 shows also for each year the number of juveniles per adult and per adult hen amonj; mallards checked in the bags of Mississippi Flyway hunters, each number corrected for the greater vulner- population between the breeding grounds and Illinois. Both shrinkage in the juvenile segment of mallard populations and seasonal
. Bulletin. Natural history; Natural history. 452 Illinois Natural History Survlv Bulletin Vol. 27, Art. b principally Illinois. It is apparent that the ratio of adult to juvenile vulnerability has no correlation with the number of juveniles per adult baj:;^ed by hunters. Table 58 shows also for each year the number of juveniles per adult and per adult hen amonj; mallards checked in the bags of Mississippi Flyway hunters, each number corrected for the greater vulner- population between the breeding grounds and Illinois. Both shrinkage in the juvenile segment of mallard populations and seasonal de- clines in the vulnerability rates of the juveniles are indicated by the progressive- ly smaller relative numbers of juveniles in hunters' bags as the ducks moved down the fivwav from Manitoba to Illinois to. JUVENILES ADULT 6 BREEDING GROUNDS Fig. 18.—Numbers of juvenile mallards per adult on the breeding grounds just prior to the hunting season, as calculated from numbers of juveniles per adult in Illinois during the hunting season; each of the Illinois numbers on which curves A, B, and C are based has been adjusted to compensate for a greater shooting loss among juveniles than among adults before reaching Illinois: A, juveniles per adult, B, juveniles per adult, and, C, juveniles per adult. ability of juveniles. For the period 1939— 1955, the corrected figure was juve- nile per adult and juveniles per adult hen. These figures probably reflect the age composition of mallard populations in the Illinois River valley for the 17-year period quite well, for inaccuracies in the yearly vulnerability rates would tend to cancel each other out over the period. Trends in the age composition of mal- lard populations in the Illinois River valley reflect trends in the age composi- tion of mallard populations on the breed- ing grounds prior to the hunting season. However, population figures obtained in Illinois do not represent the tr
Size: 2106px × 1187px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
