Bowerbirds Dance, Decorate to Suit Females' Changing Tastes

Bijal P. Trivedi
for National Geographic News

April 14, 2004

As a woman matures, so does her taste in men. What attracts her at 20
will most likely differ when she's 30. Female bowerbirds, it seems,
share these age-specific preferences when it comes to choosing mates.

A new study finds that a young, inexperienced, female bowerbird judges a male by the manner in which he decorates his bachelor pad. Once she's aged and mated a few times, this affinity for a swanky domicile fades, and she then relies on courtship routine—a vigorous song and dance—to select the most worthy suitor.

This research suggests that feminine taste, throughout the animal kingdom, may be more complicated than anyone thought.

The process through which a female satin bowerbird (Ptilonorhynchus violaceus) chooses her mate illuminates a relatively unexplored area of sexual selection—a theory that Darwin first proposed in 1871.

Darwin noticed that females are attracted to "fancy males" with lavish traits that appealed to the ear and eye: bright feathers, long tails, intricate songs, and complex dances. But little research has investigated how the female weighs these fancy traits against one another.

"Not all females find the same trait attractive," said Seth Coleman, a doctoral candidate in behavioral ecology at the University of Maryland in College Park, and co-author of a report that appears in the April 15 issue of the science journal Nature. "We think males have evolved complex mating rituals and a diverse collection of [fancy] traits to appeal to as many females as possible."

"The best males will have it all," said Coleman, who conducted a three-year satin bowerbird study in the Australian bush. The top male bowerbirds have what might be called artistic talent and vigorous courtship routines.

The Courtship Dance—The Buzz-Wing-Flip

Until recently people assumed that all females of a particular species preferred the same traits. We now know, based on Coleman's work, this is simply not true, said Stephen Nowicki, an evolutionary ecologist at Duke University in Durham, North Carolina. "This is a significant advance in the study of sexual selection."

Male bowerbirds are famous for their courtship rituals. They carefully decorate their bowers—U-shaped platforms built from twigs and grass—with strictly blue objects like berries and flowers, and even bottle caps and string, to attract prospective mates.

When a female pays a visit, she crouches in the bower and lets the male strut his stuff. He embarks on a frenetic physical display dubbed the buzz-wing-flip—an elaborate dance during which he fluffs up his feathers, produces buzzing vocalizations, and runs back and forth. The male performs this maniacal dance four times. Once he's finished, the female is off to the next bower, reserving judgment until she's sampled more performances.

Coleman and former lab mate Gail Patricelli, now a postdoctoral researcher at Cornell University in Ithaca, New York, suspected that young females are frequently startled by the males' spirited song and dance. The scientists classify the young females as "first years" and "second years" (those with no prior mating experience or just a single mating, respectively.)

"Their retreat is so hasty—often leaping up and out of the bower—that they can't possibly have any time to assess the male," Coleman said. (Sensitive males actually modulate this display to match the body language of the female. If she appears frightened, he tones it down. If she is secure, then he cranks up the level for his most intense performance.)

Finding a Quality Guy

The researchers speculated that the younger females use different indicators to size up a male—perhaps the bower with its blue ornaments. Blue objects are rare in the bowerbird environment, and a male whose bower is adorned with many is deemed superior, because it proves he is able to acquire and retain these items in the face of competition from other males.

To test their hunch, the scientists augmented a bowerbird group's environment with blue tiles and plastic strands and left another group untouched. Males from the blue-item-rich group quickly incorporated the blue decorations into their bowers.

Using video cameras, the researchers observed females at each of the three stages of courtship.

The first step in the mate search involves visiting a bower while the male is absent. Males with poorly constructed or asymmetric bowers or a haphazard arrangement of blue items are generally less successful at this stage.

Females impressed by the bower generally return for stage two—the buzz-wing-flip. After the performance the females leave for about a week to build a nest. They return for stage three, where they review encore performances from only the most promising candidates. Once they've narrowed their search to one, they mate.

Coleman discovered that in the absence of a male, all females, regardless of age, were more impressed by the augmented bowers and returned to these sites to view the male.

Decorating vs. Singing and Dancing

For the younger, less experienced females, this was the end of the story—they chose the males with the most blue ornaments because they couldn't tolerate the courtship. The three-plus-year females (with two or more years of mating experience), on the other hand, went with the physical displays, regardless of whether the bower had more curios.

The physical display is believed to be a more honest indicator of male quality. Blue ornaments can be stolen from another bower, but a buzz-wing-flip cannot be faked. "Only males in top physical condition are able to produce vigorous performances—something that sick or weak males can't do," Coleman said. Vigorous displays suggest a strong male with desirable genetic qualities.

"Not much attention has been given to female preferences and how this influences sexual selection, in part because the work is time consuming and laborious to follow individual females back and forth and record their preferences," said John Endler, an evolutionary biologist at the University of California, Santa Barbara.

"What Seth's group has achieved is outstanding—he has shown that females are assessing multiple traits. This is almost certainly true in other species, but no one bothered to ask."

Fortunately for the young female bowerbirds, good decorating skills correlate with high energy—so both young and old females tend to mate with the same group of top males. For bowerbirds, males that can sing, dance, and decorate get the females. That's a combo that could work for humans as well.