"This suggests that mimicry is pretty important in the final decision of mate choice," Coleman says. He described his results at the Conference on Acoustic Communication by Animals, hosted by the University of Maryland in July.
Among bowerbirds, "(the mating system) is like a singles bar," says Jack Bradbury, a behavioral ecologist at the Cornell Lab of Ornithology. Males want to mate as widely as possible to spread their genes. But females, who do the parenting, need to discriminate for mates of good genetic stock—helping ensure survival of the offspring.
Coleman carried out his field work at Wallaby Creek, about 90 miles southwest of Brisbane, Australia, within a 3 square mile (8 square kilometer) plot of forest in Tooloom National Park. More than 250 species of birds inhabit the park, a favorite of birders.
Good Mimics, Many Mates
Coleman rigged up 35 motion-sensitive cameras and microphones—one per bower. Each research season—from September through December—the cameras recorded about 4,000 hours of bowerbird activities.
Back in the lab, Coleman analyzed the vocalizations using a software program called Canary, developed by the Cornell Lab. Canary creates a spectrogram, or visual representation of each bird call.
Coleman produced spectrograms for each of the bowerbird's mimicked calls, then compared them with spectrograms for the model species.
The research shows that the best mimics with the broadest repertoire were most successful at wooing the females. The top males mimicked four or five species with accuracy and mated with 25 different females in one season, according to Coleman.
A poor mimic could only imitate the vocalizations of one or two species.
"(A poor mimic) sounds like a kookaburra with bronchitis," says Coleman, "and doesn't mate with a single female. These guys are probably lifelong losers."
The quality of mimicry may reveal something about a general ability to learn, Coleman speculates.
"Females need a way of getting honest information about a potential mate," says Bradbury. "Some species engage in courtship feeding, which tests the males' ability to gather food. Canaries, which sing incredibly complicated songs, can only do so when they are in good shape."
Stephen Nowicki, an evolutionary ecologist at Duke University in Durham, N.C., has proposed that what females really want in a male is a good brain. He and his colleagues have shown that when song sparrows get less food when young, their brain is smaller, inhibiting their ability to learn songs—and to lure mates.
"Seth's work is significant because he has identified yet another of these 'fancy traits' that females use to select a mate," Nowicki says.
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