In 71% of all songbird species with available data, the female sings too. This is remarkable because in the wake of Darwin's theory of evolution, birdsong has generally been seen as a characteristic of male birds, allowing them to compete with other males and attract females.
Leiden biologist Katharina Riebel published this finding on 4 March in Nature Communications, together with an international team.
Message to Darwin: Birdsong is not all about sexual selection
The team studied the available literature on the song of female songbirds. This resulted in the first worldwide survey and the first study of song in females of primitive songbird species. The team used a genetic databank to map the characteristics and evolution of these female songbirds. Their analysis shows that in the common ancestors of modern songbirds of both males and females must have had song. Leiden biologist Riebel says that 'the origin of birdsong must therefore lie not only in sexual selection and competition among males, as suggested by Darwin. It seems more probable that sexual and social selection also played a role in females: song allowed both males and females to compete for the resources necessary for survival and reproduction.'
Female birds have a voice of their own
The current view is that competition for partners led to the evolution of bright colours and a loud song in males, together with substantial sex differences in the brain while the need to avoid predators led to relatively unobtrusive female birds with camouflage colours. Riebel: "Our study disputes the general validity of this view by showing that a) singing female songbirds are very widespread and b) both the females and the males of the ancestors of all modern songbirds must have had song. This means that the preference of females for singing males cannot have been the first and foremost reason for the evolution of song. This is a starting point for alternative scenarios, that so far have not been taken into consideration in birdsong research."
New research questions
The exciting question now is how females apparently repeatedly lost their song in the course of evolution. Why did they stop singing in some lineages, but not in others? And did the pronounced brain sex differences arise each time the females lost their song? Does this mean that the exceptional adaptations for singing and vocal learning in the bird brain and the underlying neural and molecular networks can easily be switched off?
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