According to recent research at Lancaster University, male birds that can accurately repeat song tones have the best chance of attracting a female. Male birds need to make sure they have a variety of songs in their repertoire if they are to keep the female bird’s attention and prevent her from getting bored.
Over two years, researchers recorded and analyzed 7,000 breeding songs of wild blue tits in nest boxes near Lancaster University. They devised an experiment in which they played recordings of songs to receptive females and found that male vocal consistency repeating the same pattern of notes with high precision was a key feature of song that elicited sexual arousal in females.
While singing exact duplicates of the same note was sexy, it became “boring” for women. Their response gradually faded (habituated) until it flared up again when the males switched to a different song type.
The results may explain why birdsong in most species is not hypervariable and constantly changing, but shows some slight variation balancing a reliable signal of quality with the need to avoid the female becoming habituated and losing interest.
Researchers believe that a male bird’s ability to consistently hit the same note in song is a signal to females and competitors that they have strong motor skills that translate into other essential qualities of a good mate.
Lead author Dr Javier Sierro, whose PhD thesis at Lancaster University included the work, said: “In songbirds, singing requires the bird to perform complex motor patterns. Hitting these repetitive notes precisely is a way for a male bird to demonstrate these traits to potential mates, which also relate to social status, reproductive performance, longevity, sexual attractiveness, and the ability to defend territory.
“Many bird species produce trilled songs where the same note is repeated in rapid succession. The song may also be repeated during the singing match. Repetition is needed by the male to improve his singing skills, but this repetition can be expensive as the female loses interest over time.
“We found that when males sing different types of songs or insert quiet pauses between songs, it reduces the female’s habits and helps keep her interested.”
The study also showed that male bluefins with higher vocal consistency had higher reproductive success as measured by the number of eggs in their nest – further evidence that vocal consistency is a skill found in quality individuals – those who will contribute genes to future populations. Other song characteristics, such as variety, were not correlated with clutch size.
Vocal consistency increased during the breeding season, peaking between 7 and 10 days when his mate was most fertile, laying eggs daily.
The researchers suggest that a balance between two crucial aspects of birdsong, consistency and variety, may resolve a long-standing paradox in studies of bird communication and explain the level of variability in song styles between species.
Dr Selvino de Kort, from Manchester Metropolitan University and co-author of the study, said: “Our results explain why most birds repeat song structures and do not sing in a way that promotes song diversity by constantly creating new tones or song types.
Dr Ian Hartley of the Lancaster Environment Center at Lancaster University said: “Birdsong appears to have evolved under opposing selective effects, which may lead to a balance between repetition to achieve the ‘sexiest’ song and variety between songs to reduce psychological strain effect of habit.”
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