Differential Responses of Male and Female Pintail Ducks to Decoys

Abstract

Field tests employing 3 variations in sex ratios (50:50; 100:0; 0:100) of pintail decoys revealed a higher proportion of male pintails (Anas acuta) responded to the decoys than existed in the local population. These results contrast with those of the canvasback (Aythya valisineria) where Olson (1965) found that females were especially vulnerable, perhaps contributing to the imbalance in the continental population of this species. The sex ratio and other characteristics of decoy arrangements may be a useful tool in managing the annual waterfowl harvest, and a vulnerability pattern for pintails is suggested for this form of management. J. WILDL. MANAGE. 41(4):657-661 In 1918 bird banders and field naturalists realized that the sex ratios of certain ducks, especially diving ducks (Aythya), were disproportionate (Erickson 1943). The imbalance, favoring males, is in contrast to the more or less balanced sex ratios among puddle ducks (Anas) (Beer 1945, Smith 1946, Johnsgard and Buss 1956, Hochbaum 1959: 15, Anderson et al. 1969). However, the sex ratios for both diving and puddle ducks do not differ from the expected 50:50 distribution at fertilization, hatching, or among juveniles yet the imbalance is clear among adults as noted by Hochbaum (1959:51), Sowls (1955:164) and especially Bellrose et al. (1961:405). One must therefore assume that some phenomenon affects the sex ratios of diving ducks after the time each cohort attains flight. Olson (1965) proposed that hunting, as measured by the differential response of each sex to decoys, resulted in higher mortality of females. Earlier, Trippensee (1953:194) and Hochbaum (1959:150) also suggested that hunting may be the responsible factor for imbalanced sex ratios but Mendall (1958:225), in his study of the ring-necked duck (A. collaris), felt that the effects of hunting might in fact bring sex ratios into balance. We designed experiments to test Olson's (1965) conclusions on a common puddle duck, the pintail. If the hypothesis is correct there should be no difference in the response between males and females to decoys as the sex ratio of the continental pintail population is nearly in balance and thus presumably unaffected by hunting. Our objectives were to determine if sex classes of pintails respond to pintail decoys differentially and to compare Olson's data for a species exhibiting an imbalanced sex ratio (the canvasback) with data for a species showing far less imbalance in its continental population (the pintail). Our study is confined to pintail ducks wintering in the Texas Panhandle. We are indebted to the Max McGraw Wildlife Foundation of Dundee, Illinois, for financial assistance and to M. K. Rylander for his critical review of the manuscript.