How Did the Peacock Get His Tail?

Sanjida O'Connell
The Independent (London)
September 9, 2002

How did the peacock get his tail? It sounds like a Just So story, but it's a question that has tormented zoologists for more than a century.

It was Charles Darwin who first noted that it is the choosy peahen who plays a crucial role in the evolution of this extravagant sexual display.

"We may conclude that…those males which are best able by their various charms to please or excite the female, are under ordinary circumstances accepted. If this be admitted, there is not much difficulty in understanding how male birds have gradually acquired their ornamental characters," Darwin wrote.

He continued: "In all ordinary cases, the male is so eager that he will accept any female, and does not, as far as we can judge, prefer one to the other."

At the time, Darwin's theory on female choice in animals, and birds in particular, was revolutionary, and he spent pages justifying a bird's appreciation of beauty and the quality of "love" that must be felt between a pair bonding for life.

More recently, biologists have delved into the reasons why birds have large, showy ornaments, like the peacock's train, which, as Darwin noticed, hamper the ability to escape from predators.

A study published earlier this year in the journal Behavioural Ecology shows that a male's plumage is a direct indicator of the strength of his immune system; a signal to females of his internal workings.

Growing Insight

In the early 1980s, biologist Malte Andersson carried out some seminal research in the area of female choice. Andersson studied long-tailed widow birds, whose males have tails one and a half meters (4.5 feet) long and court by jumping in the air. In the prairies where they live, they can be seen for a kilometer and a half (nearly a mile).

Andersson cut some males' tails short, down to 14 centimeters (5.5 inches), and elongated other males' tails. He was able to show, for the first time, that females do choose, and what they want are males with long tails, preferably artificially enhanced.

A decade later, Marion Petrie of Newcastle University, observed a group of male peacocks, and then clipped the eye spots out of half of the males' tails. She did not reduce the tail length, only the number of eye spots. She discovered that females preferred males with the most eye spots.

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