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Although it isn't the case for all birds, many species do show sexual dimorphism, a difference in appearance between the sexes. Examples of drab females partnered with downright gaudy males include cardinals, mallard ducks, yellow finches, pheasants, turkeys and, the poster child for sexual dimorphism, the peafowl. So why are male birds such pretty boys?

* The Energy Cost of Being Showy *

The bold colors and fancy feathers of male birds become even more of a mystery when you consider what it "costs" for a male bird to put on this extravagant show. Growing fancy feathers requires energy. Consider the over-the-top tail feathers of the peacock. A great deal of energy must first go into producing the raw materials and then growing that gigantic display piece (not to mention carrying it around all the time). And even in the case of less extreme males, it takes more energy to produce colorful feathers than it takes to grow drab plumage.

* Bright Feathers and Predation *

These bright male showoffs are certainly more conspicuous than the females. And, for an animal that is preyed upon, it's usually best to keep a low profile. Pretty boy birds are at greater risk of being eaten by predators than are their drab female counterparts.

* Yet Girls Prefer the Pretty Boys *

With all of the energetic costs and dangers of having showy plumage, what advantage could these bright feathers possibly have? The reason many male birds are so fancy-looking is that females are choosing the prettiest of the pretty-boys to mate with. Over many generations, the female birds preference for good looks has shaped the appearance of the males, making the males progressively more showy. This is called sexual selection; when the mating preference of one sex is the evolutionary force shaping the appearance of the other sex. But why would a female want a fancy male; a bird who spends his energy on appearance, and, as a result, is more vulnerable to being caught by a predator?

* Males Showing Off Their Success *

The feathers of a showy male bird are essentially an advertisement screaming, "Hey baby! Look how healthy I am! I do so well that I have extra energy to spend on these ridiculous, unnecessary feathers" (i.e. optional equipment). Fancy plumage is "bling"; akin to a male human spending a wad of cash on a luxury sports car. The ostentatious automobile is not a necessity. It is a statement of success; of having money to burn. Female birds see extravagantly feathered males as being extremely successful; as having energy to burn, and by mating with a successful male, the dowdy female bird is betting that her male offspring will inherit daddy's extreme genes for success.

For more information on animal behavior and evolution see:

* Evolution 101 Sexual Selection

* PBS Evolution Web Site

* Sources *

Campbell, N.; Reece, J.; et al. (2007) "Biology". Benjamin Cummings.

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