. Bulletin. Natural history; Natural history. August, 1961 Bellrose et ah: Sex Ratios and Age Ratios 399 traps increased as the drake percentage in the population increased (indicated by bag checks, fig. 2). In the mallard and the black duck, dif- ferences in behavior may contribute to dif- ferences in numbers between males and females trapped or retrapped. One differ- blind near the traps on Lake Chautauqua showed that, when mallards were massed around the traps, the drakes were more forceful than hens in pushing their way into the traps. Chi-square tests of data in tables 1, 2, 3, and 4 indi
. Bulletin. Natural history; Natural history. August, 1961 Bellrose et ah: Sex Ratios and Age Ratios 399 traps increased as the drake percentage in the population increased (indicated by bag checks, fig. 2). In the mallard and the black duck, dif- ferences in behavior may contribute to dif- ferences in numbers between males and females trapped or retrapped. One differ- blind near the traps on Lake Chautauqua showed that, when mallards were massed around the traps, the drakes were more forceful than hens in pushing their way into the traps. Chi-square tests of data in tables 1, 2, 3, and 4 indicate that in both the mallard 80 75 70 65 60 55 50 45 Trap Cotches. 2nd 3rd 4th OCTOBER 1st 2nd 3rd NOVEMBER 4th 1st 2nd DECEMBER 3rd Fig. 2.—Week-to-week changes in the drake percentage of the autunnn flight of mallards in Illinois, as indicated by two sampling methods: checks of mallards in hunters' bags and inspec- tion of mallards caught in banding traps. Bag data are for the Illinois River valley, 1939-1949; trap data are for Lake Chautauqua, 1939-1944 and 1947. ence in behavior is the greater aggressive- ness of the drakes; this may occur because of differences in food demands during the fall. Studies on food consumption of penned wild mallards (Jordan 1953:122) revealed that, during the fall and winter, drakes consumed 15 per cent more food than did hens. Observations made from a and the black duck the propensity of drakes to enter traps was significantly greater at Lake Chautauqua than at Mc- Ginnis Slough. The population density was much greater at Lake Chautauqua than at McGinnis Slough. Consequently, the competition for bait at trap sites was greater, the aggressiveness of drakes was. 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 Illi
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Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
