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Waterfowl Sex Ratios

A variety of factors influence the proportion of males and females in waterfowl populations.
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Dramatic changes in sex ratios are of concern to biologists if they coincide with declines in populations. Essentially, this can be an indicator of changes in adult female mortality possibly resulting from increased stress during the breeding season and landscape changes affecting nesting success. Arnold Erickson, after conducting studies during the late 1930s in Minnesota, stated, “In general, the female that nests in a greatly disturbed environment is more subject to predation and the activities of man than the one that nests in undisturbed habitat.” This is why Ducks Unlimited has for nearly 75 years stressed the need for landscape-level habitat conservation.

Dale Humburg is chief biologist at DU national headquarters in Memphis.

Can We Take More Drakes of All Species?

While bag limits for male and female mallards and, for a time, northern pintails have been implemented over the years, there has been limited use of sex-specific regulations for other species. For sex-specific regulations to be appropriate, the following conditions must be met:
  • No difference in sexual maturity exists between males and females.

  • Surplus drakes are not important in providing mates for renesting hens.

  • An increase in drake harvest (due to differential regulations) does not also increase hen harvest.

  • Hunters can identify both drakes and hens and actively select males in the field.

Look More Closely

Differentiating drakes and hens in the field is complicated by plumage variations among species, sexes, and ages. For geese, black ducks, and mottled ducks, the plumage of males and females is quite similar, and in many instances, behavioral differences are the only way to tell the sexes apart at a distance. For sea ducks, which sexually mature in their second year, it’s difficult—if not impossible—to confidently differentiate first-year males from young and adult females. And even among species where drakes and hens have obvious plumage differences, observers have to be careful that light conditions and other visibility biases don’t affect their data collection. Drakes show up a whole lot better than drab-colored females.
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