Papua New Guinea is an island country in the Pacific Ocean. Deep in its rainforests, male birds-of-paradise gather to display. They look glorious in the morning sun. Their fine black tail feathers coil behind them in ribbons. They let out a repetitive, piercing screech to let females know they are around. Each bird's call competes with the next. When a female appears, the males begin to strut and bob. They fan their delicate feathers, each seeking the female's attention.

With their beautiful appearance, birds-of-paradise have long captured people's curiosity. They were first introduced to the Western world in the 1500s by explorer Ferdinand Magellan. He brought specimens back to Europe from the East Indies. Since then, they have been an inspiration for art and fashion.

Birds-of-paradise are found throughout Papua New Guinea. They are also spotted in the surrounding islands of Indonesia and a small part of northeastern Australia. In all, there are 39 species, each one different from the next. They come in many colors, shapes, and sizes, from the plain-looking paradise-crow to the colorful Raggiana bird-of-paradise. While beautiful, these birds are perhaps best known for their showy methods for attracting a mate.

The Superb Bird Puts on a Shimmery Show

Consider the efforts of the male Superb bird-of-paradise. He totally changes his appearance to get the attention of a female. He fans out his black feathers with a few electric-blue feathers sticking out. It makes him look a crazed smiley face. Then he hops around excitedly, making sure the female always gets his best angle. He whirs and clicks and snaps his tail in rhythm, flashing a breastplate of shimmery feathers. The female watches, showing no emotion.

His dance moves may appear unpredictable, but they are carefully planned. He is trying to convince a female that he is the best mate. The male works hard to impress, tirelessly refining his moves until the female is won over. After all, she is the one in control. She ultimately decides who her mate will be.

Bright Feathers Can Attract Predators

Stunning as it is, the male's beauty is impractical. For example, take the ribbon-tailed Astrapia. It boasts bright white tail feathers that stretch one meter (three feet) long. Such long tail feathers might help it attract mates, but they aren't exactly useful for survival.

So how did long feathers and other features evolve? Famous naturalist Charles Darwin proposed his theory of natural selection to answer the question of how certain animals end up with certain features. Natural selection is sometimes called "survival of the fittest." It means that animals with traits that help them survive will live on. A trait might be its color. It might be what they eat or how they hunt. If an animal lives long enough, its children can also have traits that help them survive. Animals without these traits might get eaten or die out.

Yet the Astrapia's trait of bright long tail feathers does not seem to offer any survival advantage. They actually might put the bird at risk. A predator could spot it easier.

Males Compete To Pass on Their Genes

Darwin had another theory to account for this. He called it the theory of sexual selection. Darwin suggested that some traits evolve for another important reason: They improve an individual's chances of attracting more or better mates. This can happen even if the traits put survival at risk.

To compare the two theories, natural selection explains evolution driven by the competition for survival. Sexual selection explains evolution driven by the competition for mates.

The dense jungles of Papua New Guinea provide plenty of food for the birds-of-paradise. There are also few natural predators. These are the perfect conditions for a specific type of sexual selection known as "female choice." Females do not need males to defend them. They can get their own food and raise their young by themselves. As a result, a female can be picky about her mate. Males have to impress if they want a chance to pass on their genes.

Females Shape the Male Bird's Appearance

Sometimes, genes combine in new ways when species mate. This can cause new traits to emerge that females find more appealing. For example, say a male crow is born with longer-than-average feathers. For whatever reason, a female crow finds long feathers more attractive than short feathers. She picks the crow with longer feathers as a mate. Their young inherit both of their parent's traits. They get their father's long feathers and their mother's fondness for them. Over successive generations, these traits become more common. More males are born with longer feathers. More females are born that prefer longer feathers. The preferences of the females actually shape the appearance of the males over time.

Male birds-of-paradise are certainly fun to watch as they strut and dance center stage. Yet there is more to their performance than first meets the eye. You are actually seeing evolution in action. Generations of picky females shaped the male's incredible appearance. They are also why the males perform in a way that seems silly to us.