Washington, Sept 5 : Duets sung by breeding pairs of some tropical bird species may sound harmonious to humans, but a new study has found that some of these birds fight by singing, using melodic tweets to defend their relationships and territories.
The University of Windsor and Cornell University team made their study possible by eight microphones positioned strategically throughout the dense tropical forests of Costa Rica.
The microphones fed the song duets of rufous-and-white wrens into a single laptop computer, enabling researchers to pinpoint the exact positions of the colourful songbirds.
"Your first impression after you hear the duet of a pair of tropical birds is one of great harmony and cooperation," said Daniel Mennill of the University of Windsor.
"Their duets require coordination and synchronization, and my multi-microphone recordings confirm that birds do coordinate their activities by performing duets.
"But there is a darker side to duetting; tropical birds also perform duets in very aggressive contexts, and respond with special aggression to rival individuals of the same sex. Their voices are beautiful harmonies, but they're also aggressive audio warfare," he added.
The researchers found that male and female wrens approach each other following duets and use them to play a version of the children's game Marco Polo.
"One bird sings, listens for the song of its partner, and moves towards their partner after hearing a response," Mennill said.
In another set of experiments, Mennill used two loudspeakers to simulate the voices of a pair of duetting wrens and found that birds fight duets with more duets.
He said that as soon as the birds heard the duets of a rival pair, their singing rate 'shot through the roof' - evidence that the melodies play an important role in aggressive territory defence.
The study is published in the September 4th Current Biology, a Cell Press publication.