Those that sing together, stay together -- at least for some birds, according to the latest study from the Cornell University Lab of Ornithology. 

Not all birds are monogamous, and when it comes to Australian red-backed fairy-wrens both sexes tend to be very promiscuous. In fact, Cornell researchers found that 60 percent of bird nests surveyed during their study contained offspring that belonged to a male who did not share the nest. Raising one's own young can be taxing as it is, so how do fairy-wrens keep from wasting energy and resources on another male's chicks? Researchers found the answer is simple: Sing with your mate. 

"The result was not expected at all," Daniel Baldassarre, of the study researchers, said in a news release. "In fact, we were actually looking into whether more aggressive males did better at preventing extra-pair matings with their mate than more timid males. We thought the aggressive males would be cuckolded less often."

Researchers tested their aggression hypothesis in the subtropical grasslands and open woodland habitats favored by red-backed fairy-wrens just outside Brisbane in Queensland, Australia. Fake fairy-wrens were set up in bushes and researchers played male song recordings to see how wrens would react.

While some birds were fierce in their territorial defense, physically attacking the fake birds to drive them off, others were more cautious. However, aggressive behavior made no difference, as the males' mates were just as unfaithful. 

Instead, researchers discovered pairs were less likely to mate outside of their pair bond when they sang together more. In other words, those that began a duet quickly after detecting an intruder and sang duets more often had lower rates of infidelity. This is what researchers call a "strong" duet-singing response. 

"The male and female will immediately fly together and perch on a branch right next to each other and start belting out these duets," Baldassarre added. "If the males are particularly riled up, they will do this 'puff-back' display, raising the orange or red feathers on their back to the intruder. While singing duets, their heads are thrown back to the sky with their beaks wide open."

Next researchers hope to study what exactly is going on during these duets and who is taking the lead. 

"The big picture question is about how animals make mating decisions," Emma Greig, one of the study researchers, explained in the university's release. "Our results suggest the females are deciding what males to cuckold (cheat on). Females are either being influenced by their mate's songs, or females are indicating their own choice by singing with their mates more. We need more detailed work to distinguish these alternatives."

Their findings were recently published in the journal Biology Letters

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