Songbirds, of course, are known for their singing. This is usually limited to the males, but certain songbirds sing duets with their mates. Especially impressive among these duos are those birds that sing antiphonal duets, in which the male and female sing alternating phrases back and forth. These duets can sound so seamless that the human ear may mistake them for a single bird.
The sonogram shows that what you’re listening to is actually an antiphonal duet; the contributions of the two birds are shown in red and blue.
When Chris Templeton of the University of St. Andrews listens to such duets, he wonders how the birds are able to coordinate their separate songs into such a complex duet. In a recent study, Templeton and colleagues tested duet integration in happy wrens, a duetting species native to the forests of western Mexico.
Singing perfectly timed antiphonal duets is perceptually and cognitively challenging. Each happy wren has a repertoire of about 40 different sex-specific song phrases, which can be combined and repeated to form a song. Different phrase types vary in length and pairs sing duets even when separated by several meters distance. What’s more, each pair has its own rules about how to combine phrases. In one pair, the male may reply to the female’s phrase A with his own phrase X and to her phrase B with his phrase Y. But a different pair might combine these same phrase types as duets AY and BX. Thus, this coordination requires both selecting the appropriate phrase and timing it exactly right, all in less than half a second.
Templeton and his colleagues caught male happy wrens and played back pieces of their mate’s song to them. These birds were from a population the researchers have been studying for years: mapping their territories, recording their songs, and marking the birds with plastic identifying rings. The playback consisted of a single phrase type from each male’s mate, repeated at various intervals. The researchers varied the distance of the recording and the tempo of the female’s song to see how the males coordinate their songs to produce duets.
Templeton and his colleagues report the males’ responses to the playback were surprisingly rapid. None of the male wrens sang before the playback started, and five of eleven responded immediately to the very first female song phrase, just a fraction of a second after its start. This suggests that almost instantly, the male wrens were able to recognize the playback as a happy wren song, and specifically as their own mate’s song.
Males were also good at matching their tempos to that of the playback, even as the researchers manipulated the playback rate. The male wrens were more likely to respond to closer playbacks than more distant ones. Since the purpose of the happy wren’s duet is thought to be territorial defense against intruders, Templeton and his colleagues suggest males may be reluctant to sing when their mate is further away. This could be because it is more difficult to maintain duet precision at greater distances, or the male may not want to advertise to intruders that he is far away from his mate.
The males also tended to reply with the correct phrase from their own repertoire, although they didn’t follow their duet code exclusively. All males sang the correct phrase at least once, and eight of eleven used the correct phrase most frequently, but the birds tried other phrases, as well. Templeton and his colleagues suggest this could be an attempt by the male to lead the female in the duet. Males generally lead duets, so when he changes the phrase type, she normally follows. In this case, the recording, of course, did not follow his lead. During the experiment, several males switched back to using the original, correct phrase type after their simulated mate failed to follow their lead, implying that while the male generally leads, he is also attentive to his mate’s singing.
Templeton says much of the research on duetting has focused on their function, while very little is known about how duetting birds coordinate their songs. “Our work has demonstrated that happy wrens achieve the remarkable precision in duetting through constant and careful attention to their mates,” he says.
That kind of devotion is enough to make any girl happy.
All images by Chris Templeton.
Templeton, C. N., Mann, N. I., Ríos-Chelén, A. A., Quiros-Guerrero, E., Macías Garcia, C., and Slater, P. J. B. (2013). An experimental study of duet integration in the happy wren, Pheugopedius felix. Animal Behaviour 86: 821-827. http://dx.doi.org/10.1016/j.anbehav.2013.07.022