Robotic Female Lures Male Bowerbirds Into Experiment

A feathered robot built by a University of Maryland mechanical engineering professor and students helped Maryland biologists discover a new twist in the mating ritual of Australia's amazing bowerbird.

In a paper to be published in the Jan. 17 edition of the journal Nature, biology graduate student Gail L.Patricelli, professor of biology Gerald Borgia, and associate professor of mechanical engineering Gregory Walsh show that the fellows who have the most success are the ones who can adjust the intensity of their mating dance if the female signals that she is uncomfortable.

"The male satin bowerbird puts on a very intense mating display, which is important for wooing the female," said Patricelli, who designed the experiment for her doctoral dissertation with Borgia. "But if it gets too aggressive and threatening, it also can startle her. Our experiment showed that the preferred males were those who could give a highly intense display but who could tone down the intensity to avoid startling the female.

"The less successful males either didn't pick up on the female's signals and were scaring her, or they were not displaying intensely enough."

The team's discovery reveals a new characteristic in understanding how males in polygamous species attract females. "Our observations of bowerbirds, that male display is very aggressive and that females are often startled, started us thinking that females might be threatened during display, and, for the benefit of both, females should signal their level of comfort with the males' display. Our experiments supported this view."

To determine the finer points of bowerbird sexual prowess, the Maryland team built a remote-controlled, realistic femme fatale that could mimic the movements of a real female satin bowerbird. Called a fembot, the remote-controlled flirt gives off all the subtle signals a male needs to figure out if the lady is interested. The fembot turns her head, fluffs her wings, tilts her beak and can assume the mating stance, a slow crouch with a tip.

"We wanted to control the signals given by females during courtship," said Borgia, who has been studying the bowerbird for 22 years. "Females have fewer moves than the male in courtship, so we could realistically duplicate the female's behavior with a mechanical bird."

Gregory Walsh, who, with his students, designed and built the robot after watching videotapes of the birds in their Australian habitat said, "It was tricky but not terribly difficult. Robotics takes a lot of inspiration from nature. We built a sheet metal skeleton, and a taxidermist did the bird's exterior. We inserted a small computer to control the bird. Of course we called that the 'bird brain.'"

The bowerbird courtship ritual is well suited for introducing a robotic love interest, because, for one thing, it's easy to tell where mating will take place. Males in almost all of the 19 bowerbird species, found in Australia and New Guinea, begin the mating season by constructing elaborate bowers, or courting areas, to attract females.

The satin bowerbird female, a gray-green bird about the size of a turtle dove, cruises the neighborhood, checking out the bowers, and when she sees one that interests her, she steps inside. The iridescent purple male then launches into a raucous song and dance, jumping, ruffling his feathers and singing, even imitating the calls of other birds. If he gets the crouch from the female, he knows he's succeeded, and mating takes place. Sometimes a female will visit the bower several times before she consents.

The actual consummation is as quick as a ruffle of feathers, and the female is off to lay her eggs and hatch her young. Once she has found a good man, the female may return to his bower each year as long as he is sexually active.

Patricelli carefully snuck a fembot into bowers scattered along Wallaby Creek in northern New South Wales, Australia when the males were away from the sites, hid the remote control wires under leaves and waited for the males to appear. From a hidden blind, Patricelli operated the controls to send four different courtship signals, including consent. A video camera recorded the action.

The feathered robot was so accurate in its movements that more than one male attempted to mate with the fembot, but it took several years to refine the fembot into her current svelte size. "Our prototype was a big, healthy girl, because she was radio-controlled and had a lot of machinery hidden in her gut, " Patricelli said. "We switched to wires, which slimmed her down a lot."

The debut bird was a hit in the bower, however, said Walsh, "In the trials, two males were fighting over her and knocked her head off."

The bowerbird is the only male bird in the world known to use interior decorating and landscaping to prove his manhood to the female, according to Borgia. Different species construct different styles of bowers, from the satin's upswept 2-walled stick construction to a 6-foot wide dome-style bower built by a New Guinea species.

Borgia's research has shown that the more refined and decorated the bower, the more successful the builder is in the mating game. The top male satin bowerbirds are even clever with landscaping. Many of the species lay out colorful lawn ornaments of seeds, feathers and bright plastic baubles, such as clothespins, in neat arrays around the bower.

"The males can't wander far from their bowers," said Borgia, "because other males will steal their gear. The satins especially like to steal the blue parrot feathers."

The 36 cameras that Borgia and his team of graduate students maintain in Wallaby Creek through the mating season have shown that attention to detail in the construction of a bower pays off for the satin bowerbird.

"One very successful male who had a good bower mated with 25 females over one 2-month mating period," said Borgia. "He mated with nine females in one day. But that's the exception. Most of them don't land a female mate at all. The sexiest guys get all the mates.

"Like humans, bowerbirds have evolved a high level of intelligence, but each species has come to this point with a very different set of ancestors," said Borgia. "The example of bowerbirds has led some to suggest that in humans and bowerbirds, intelligence may have been driven by competition to show off to the opposite sex."

By Ellen Ternes, University Media Relations

Published January 16, 2002