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Female Body Language No Enigma to Male Bowerbirds, Study Finds

Bijal P. Trivedi
National Geographic Today

January 16, 2002
 
To most men, a woman's body language can be one of the most mystifying
things in the universe. But male satin bowerbirds have cracked the code.
Studies by a scientist at the University of Maryland show that male
bowerbirds modify their courtship rituals based on the females' body
language.

Male bowerbirds woo females through dramatic
behavior—ruffling and puffing their feathers, stretching their
wings, and buzzing loudly as they strut about their bowers.


But sometimes these macho displays are overly aggressive, resembling rough male-to-male encounters. This can frighten the females and abruptly end the courtship. So the males must interpret the females' body language to determine just how far to go.

According to Gail Patricelli of the University of Maryland in College Park, male bowerbirds gauge the nature of their performance by studying the females' posture.

Female bowerbirds indicate their level of interest in suitors by "crouching," or lowering their bodies and tilting forward toward a mating position. A fully crouched female also fluffs up her wings.

A female that stands or barely crouches during a display signals alarm. This tells the male to tone down his antics. A female that begins to crouch during a courting display signals some degree of tolerance—a sign that the male can intensify his display.

Robotic Decoy

Patricelli wanted to find out how male bowerbirds responded to changes in females' behavior. She asked a mechanical engineer at the University of Maryland to build a robotic bird that was capable of a few basic movements: turning its head from side to side, fluffing its wings, and crouching in several positions.

Patricelli covered the robotic skeleton with a skin from a real female bowerbird. "It looked like a museum piece, but instead of being filled with sawdust, the bird had robotic innards," said Patricelli.

With the robotic female, Patricelli and her colleagues headed to the Australian outback, where satin bowerbirds live. The researchers put the remotely controlled robotic bird in a male's bower—a retreat constructed of sticks and boughs to attract a mate—and waited for the male to return. Upon finding a "female" in its bower, the male began its courtship display.

The robot was built for three levels of crouching, from barely crouching to a deep-seated squat. Patricelli observed that as crouching became more intensive, males increased the flamboyance of their behavior.

When the robot stood in the bower, the male exercised a cautious, rather subdued display—wooing carefully to avoid flustering the prospective mate. If the robot was placed in a slightly crouched position, the male's display was a little more flamboyant.

When the female squatted and fluffed her wings, the male was highly energetic in his display—puffing up, flapping, and buzzing loudly. Squatting assured the male that the female was definitely interested and was giving the male an opportunity to show his assets.

"Natural selection favors males that are responsive to females and know how to communicate well," said Patricelli. Males that are sensitive to females' signals are more likely to mate with several females, she added.

The results are described in January 17 issue of the journal Nature.

Elaborate Courtship

The male bowerbirds courted the robotic female much as they would a real bird. "At the end of the display, some males—mystified by the lack of further interest—would simply jump on the crouching female and try to mate," said Patricelli.

Male satin bowerbirds become sexually mature at seven years old, when they acquire their trademark black plumage with an iridescent purple-blue sheen. When younger, their plumage resembles that of females, with a combination of green, gray, and brown feathers.

Often these young males are mistaken for females by sexually mature males and courted. "Young males seems to learn courtship rituals by role-playing the other side," said Patricelli.

To further impress females, the males elaborately decorate their bowers with bright blue objects: pen caps, parrot feathers, toothbrushes, baby pacifiers. "Males that have many blue decorations symmetrically arranged on their bowers are more successful breeders," said Patricelli.

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