Cape Town - Most birds are socially monogamous – they build homes together and raise kids together – but this does not extend to sex.
Take the crimson-breasted shrike: New research has established that of the females studied over three consecutive breeding seasons, 20 percent of all babies born were not fathered by their “mates”. Paternity testing proved this.
And the researchers have also found out that these sexually adventurous females indulge in a particular kind of deceit to ensure their social partners stick around and play daddy to someone else’s kids.
The research was co-authored by Michael Cherry from the University of Stellenbosch and Georg Klump from the University of Oldenburg in Germany, who both supervised doctoral research student Irene van den Heuvel.
Cherry said scientists had learnt that on average about 11 percent of baby birds in any nest were sired by a bird other than the resident male. However, duetting birds were thought to be the exception.
Less than five percent of all bird species engage in duets, crimson-breasted shrikes being one of them.
“One hypothesis is that duetting functions to re-inforce the bond between the couple, thereby reducing extra-pair mating. Other hypotheses are that duets serve in territorial defence, mate guarding and mutual recognition and maintaining contact in dense vegetation,” Cherry said.
Van den Heuvel’s study of crimson-breasted shrikes tested two hypotheses: that the birds’ practice of singing duets between males and females was used to guard paternity, and that taking part in these bird-song duets was a signal of commitment to sexual monogamy.
Not so. The researchers combined an analysis of the acoustics of duetting with a genetic analysis using microsatellite DNA marker to investigate the mating patterns of the birds. In the three breeding seasons they studied 19 pairs of crimson-breasted shrikes and 83 nestlings from 44 broods.
They found that 20 percent of the baby birds had been sired by males that were not the females’ social partners.
Then they found out why the females sing duets: It was to manipulate the males into sticking around to look after the other guy’s babies.
Cape Times