. Bulletin. Natural history; Natural history. 432 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 trapped at Lake Chautauqua or mallards bagged in the vicinity of that lake. Despite marked differences in the size of samples between trapped and shot mal- lards, the two sampling procedures indi- cated similar ^Tar-to-year trends in age ra- tios, fig. 10. The statistical correlation in the annual changes in age ratios between mallard drakes trapped at Lake Chau- tauqua and mallards shot along the Illi- nois River was found to be significant (r=+, 13 ) at the 99 per cent level. Ma
. Bulletin. Natural history; Natural history. 432 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 trapped at Lake Chautauqua or mallards bagged in the vicinity of that lake. Despite marked differences in the size of samples between trapped and shot mal- lards, the two sampling procedures indi- cated similar ^Tar-to-year trends in age ra- tios, fig. 10. The statistical correlation in the annual changes in age ratios between mallard drakes trapped at Lake Chau- tauqua and mallards shot along the Illi- nois River was found to be significant (r=+, 13 ) at the 99 per cent level. Mallards inspected in hunters' bags in the Illinois River valley (1939-1949) and mallard drakes taken in traps at Lake Chautauqua (1939-1944 and 1947) showed similar trends in age ratios for most of the hunting season, fig. 11. The trends tended to be parallel except in early December. The correlation between age ratios calculated weekly for the samples 70r- Trap Catches 2nd 3rd OCTOBER 2nd 3rd NOVEMBER 1st 2nd 3rd DECEMBER Fig. 11.—Week-to-week changes in the adult percentage of the autumn flight of mallards in Illinois, as indicated by two sampling methods: checks of mallards in hunters' bags and inspec- tion of mallard drakes caught in banding traps. Bag data are for the Illinois River valley, 1939- 1949; trap data are for Lake Chautauqua, 1939-1944 and Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Illinois. Natural History Survey Division. Urbana, State of Illinois, Dept. of Registration and Education, Natural History Survey Division
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