Researchers at the University of Exeter discovered that males in poor condition could vary their song to give a false impression to stranger females. But they did not even try to fool familiar females, who use song as a reliable test of their underlying qualities.
The scientists studied zebra finches to establish how trustworthy birdsong was in providing honest signals about the male’s value as a mate. Singing is a test of the condition of birds because it uses a lot of energy. Fit and healthy birds are thought to be able to sustain a high song rate for longer, making them more attractive to females.
Dr Sasha Dall, of the University of Exeter, was involved in the research. He said: “Every man wants to cast himself in a favourable light when he meets an attractive female, and we have shown that birds are no different. But just like many humans, it seems zebra finch males are unable to dupe females who know them well enough. When the birds were in an established relationship, the female could tell the true condition of a male by his song, and judge whether he would make a good father for her next brood.”
The team studied 91 male and 91 female birds from a colony in France, and 12 of each gender from a colony in the UK. In the study, there was no difference in the singing of male single birds in encounters with unknown females. But, when in front of their partners, birds who were in good condition sang at a higher rate than those in poor condition.
Dr Morgan David, who led the research, said: “This is the first study to find evidence that the link between male body condition and birdsong differs depending on the context of the encounter with the opposite sex. It could have significant implications for learning more about the evolution of courtship patterns such as birdsong.”