Since the wren's brain responses were stronger for duets than for any other sound, it appears that their brains are wired for cooperation.

Deep in the cloud forests of Ecuador, on the slopes of an active volcano, there lives a chubby, unassuming looking bird known as the plain-tailed wren. As the name implies, it does not look extraordinary, but there is something extraordinary in the way this bird sings. The plain-tailed wren is famous for its unusual duet, where the vocalizations of a male and a female meld so seamlessly that one might think it was a single bird singing.

“What’s happening is that the male and female are alternating syllables, thought it often sounds like one bird singing alone, very sharply, shrilly and loudly,” explained John Hopkins behavioral neuroscientist Eric Fortune.

In order to examine how sensory information from each wren is used to coordinate singing between individuals for this cooperative behavior, Fortune and his colleagues listened to more than 1,000 wren vocalizations captured in over 150 hours of recordings. They found that wrens commonly sang duets, but both males and females also sang on their own as well. The structure and sequence of syllables sung in duets and solitary singing were identical—with gaps in the individual song where the partner would normally sing. But during a solo, the duration of gaps between sung syllables varied more significantly. This suggests that sensory cues affect the duration and variability of the gaps, and that the birds do not use a fixed pattern to sing.

To learn how cooperative duet singing was encoded in the brain, the researchers captured 6 birds and monitored brain activity in the area that controls singing. They recorded up to 30 hours from each of the three female and three male wrens, and then played back isolated “units” from the recordings. These various pieces included both duets and isolated syllables, and the researchers manipulated some of them, reversing a clip in its entirety or presenting each syllable in reverse order. The researchers expected to find that the brain responded most to the wren’s own singing voice, but both females and males responded best to the duet.

“We found that the brain of each individual participant prefers the combined activity over his or her own part,” said Fortune. Since the wren’s brain responses were stronger for duets than for any other sound, it appears that their brains are wired for cooperation. Because the neurotransmitter systems that control brain activity at the molecular level are nearly identical in all vertebrates and the layout of the brain structures is the same, the brain mechanisms observed in the wrens could hint at the same ones used for cooperative behavior in other vertebrate species. (Written by Allie Wilkinson, Ars Technica)

[For further information, follow this link at Science Magazine]