Male birds who can repeat song notes attract female mates: Study

LONDON: Male birds who can accurately repeat song notes have the highest chances of luring a female partner, according to recent Lancaster University research. The research was published in the journal 'Nature Communications.'

Male birds must have a diverse repertoire of songs if they are to keep a female bird's attention and keep her from becoming bored. The researchers recorded and analysed 7,000 songs of wild blue tits breeding in nest boxes near Lancaster University over the course of two years.

They devised an experiment in which they played song recordings to receptive females and discovered that male vocal consistency - the ability to repeat the same pattern of notes with high precision - was the key song feature that elicited sexual excitement in females. While singing exact duplicates of the same note was sexy, it became 'boring' for females. Their response gradually faded (habituated) until it was rekindled when males switched to a different type of song.

The results may explain why birdsong in most species is not hypervariable and constantly changing but shows some moderate variation - balancing the reliable signal of quality against the need to avoid the female habituating and losing interest. The researchers believe that a male bird's ability to consistently hit the same note in a song is a signal to females and competitors, that they have strong motor skills, which carry over to other essential qualities in a good mate.

Lead author Dr Javier Sierro, whose PhD thesis at Lancaster University included this work, said, "In songbirds, singing requires the execution of complex motor patterns within the bird. Precisely hitting those repetitive notes is the way a male bird can demonstrate to potential mates these qualities, which also cut across social status, reproductive output, longevity, sexual attractiveness and ability to defend territories." "Many bird species produce trilled songs where the same note is repeated in quick succession. A song may also be repeated during a singing bout. Repetition is needed by the male to perfect his singing skills, however, this repetition may carry a cost where the female loses interest over time."

"We found that when males sing different song types or introduce silent pauses between songs, it reduces female habituation and helps retain her interest," said Dr Javier. The study also showed that male blue tits with higher vocal consistency had higher reproductive success as measured by the number of eggs in their nest - further adding to the evidence that vocal consistency is a skill found in good quality individuals - those who will contribute genes to future populations. Other song features, such as diversity, were not correlated with clutch size.

Vocal consistency increased over the breeding season and it peaked during the 7 to 10-day period when his female partner was at her most fertile when she laid an egg daily. The researchers suggest that a balance between the two crucial aspects of birdsong, consistency and diversity, may resolve a long-standing paradox in studies of bird communication, and explain the level of variability in singing 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 advertises song diversity, by continuously producing novel notes or song types." Dr Ian Hartley, from the Lancaster Environment Centre at Lancaster University, said: "Birdsong seems to have evolved under opposing selective effects, which may result in a balance between repetition to achieve the 'sexiest' song, and diversity between songs to reduce the psychological effect of habituation."