Several studies have been conducted on birds to test these theories. Male house finches, which have brightly colored plumage, were altered to appear brighter or duller than normal. Those dyed brighter were chosen most often, and all obtained mates. Only 30 percent of those dyed a duller color obtained mates. Similar findings were observed in swallows that had their tail feathers artificially elongated or shortened. Apparently, female swallows like longer tails. All the males with extended tails were chosen as mates, and those males actually produced more offspring. All animals are not the same, as each species tends to key in on different male traits.
What makes a drake attractive? In the dabblers that have been studied, courtship displays and plumage characteristics have been shown to be among the most important determinants in mate choice. In both mallards and pintails, males with more vigorous courtship displays are chosen more often than less active males.
Male mallard plumage characteristics important for female choice included a full green head and normal, brown chest. When researchers cosmetically degraded the appearance of drakes by plucking breast and head feathers to create a “beat up” look, hens chose the unaltered, “good-looking” males. Hen pintails preferred males with clean white breasts and more colorful scapulars, but surprisingly tail length didn’t appear to be a factor.
As for the hens, there is an advantage to being dull and boring—camouflage. Because female ducks basically go it alone while nesting, they suffer a higher mortality rate than males. As all hunters know, there is great advantage to blending into your environment. Female ducks are dull and brown so that they blend into the vegetation on their nesting areas, such as native grass or brush. It just doesn’t pay to attract unwanted attention when trying to incubate a nest full of eggs.
All of this raises the question: Why do male and female geese and swans look similar? Both geese and swans pair for life, and according to theory, the pressure for selection is therefore reduced.
Dr. Tina Yerkes is director of conservation planning at DU’s Great Lakes/Atlantic Office in Ann Arbor, Michigan.