Like a stereotypical husband who pretends not to hear his wife berating him, some male songbirds show no signs of recognizing the call of their long-term mate in laboratory settings. But recent work with these animals finds that they can, in fact, differentiate their mate's voice but will react to it only in certain social situations.
Zebra finches are monogamous songbirds from Australia that fly in large flocks. As a result, couples routinely lose visual contact of each other and use calls to keep in touch. Whereas the female zebra finch clearly responds to the sound of her partner, the reciprocal behavior had not been observed in the male. Clémentine Vignal of Jean Monnet University in Saint-Etienne, France, and her colleagues acoustically analyzed the calls of seven female finches to see whether they had distinguishing characteristics. The results, published today in the journal Nature, demonstrated significant variation in the songs of the female birds, implying that the males could in all likelihood identify their sweethearts if they put their minds to it.
To test this hypothesis, the researchers observed the reactions of male zebra finches while recordings of their mates were played back. Unlike previous setups in which the male was alone in a cage, the team placed other zebra finches nearby. As in previous experiments, the male made no display of recognition to his mate's voice in the company of either two males or a male and female who were not mates. Interestingly, however, when a mated couple was in the next cage, the male made it clear that he knew his mate's voice by nearly doubling the rate of his own calls.
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Prior to this work, the ability to judge social context had been observed only in primates. "It really is a big finding because it shows that these birds can make social assessments like bigger-brained animals," remarks Christopher B. Sturdy of the University of Alberta, who authored an accompanying commentary. Sturdy suggests that the main function of the male's response is "to advertise that 'she's with me.'" But he is at a loss as to how to explain why the male does not have this advertising urge when in the presence of competitive suitors, because human analogies only go so far.