By Tina Yerkes, Ph.D.
Somehow it just doesn’t seem right that drakes are decked out in attractive colors and eye-catching patterns while hens are dull brown and boring. A theory called sexual selection accounts for this arrangement in many birds. In waterfowl, this is common among species—primarily dabbling ducks—that select new mates each year.
The basic idea behind sexual selection is that the sex that chooses a mate is the one that drives the development of characteristics that make the species successful. Female ducks choose their mates, and that results in drakes having to compete for hens. According to this theory, males with the right stuff win, and those traits are passed on to their offspring. The signals that indicate the right stuff may include large body size, fancy plumage, intricate songs, or striking displays. The tail of a male peacock is a good example of an exaggerated difference between males and females.
Dabbling ducks are seasonally monogamous, which means they choose new mates each year, generally on the wintering grounds. These pair bonds break once the female begins incubation. Males neither help incubate the eggs nor raise ducklings. They do, however, escort and guard females while they are paired, allowing hens to spend most of their time feeding. This behavior likely allows females to increase their foraging efficiency and improves their chances of nesting successfully when they reach the breeding grounds.
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Although being choosey appears to provide few obvious advantages for hens, the benefits may be hidden. Hens may indeed be choosing good genes. The “good genes” hypothesis states that exaggerated male plumage or courtship displays truthfully signal genetic or physiological superiority. Another aspect of this concept is the “sexy son” hypothesis, which proposes that female choice is based on the genetic advantage passed on to her male offspring. For example, females that prefer to pair with larger males should produce large sons as well as daughters that show a preference for larger males. This process can escalate over time, resulting in increasingly exaggerated male traits and stronger female preference for those traits.
How do females determine which male has the best genes? According to this theory, females assess characteristics such as color, ornamentation, and vigorous behavior that may be related to better genes. In ducks, males perform courtship displays for females in courting parties, and females choose among displaying drakes. Studies have shown females choose males that are more active in courtship displays and are the fashion icons of the group. They likely choose these flashy looking males because they appear stronger and healthier and likewise will be more capable of protecting them while they feed on wintering areas and during spring migration.