Risky ... female Gouldian finches play the field. Photo: Sarah Pryke
SNEAKY sex with a male other than your partner makes for healthier offspring, at least when it comes to the exquisitely plumaged Gouldian finch, Australian researchers have found.
The female Gouldian finch regularly cheats on her mate to maximise the chance of robust offspring, even though the male is more likely to shirk fathering tasks if she is found out, Macquarie University biologists Simon Griffith and Sarah Pryke revealed.
The practice is ''an insurance policy against the possibility that their partner isn't very good'', Dr Griffith said.
Like humans, birds often form monogamous partnerships for parenting, but this is fraught with risk for the Gouldian finch, which has an unusually high rate of intra-species incompatibility.
The diminutive native Australian bird has a head in one of three colours: black, red and yellow. Curiously, black-headed birds are genetically incompatible with red-headed birds, studies have found.
A previous experiment by Dr Griffith and Dr Pryke determined that offspring born to parents of this head-colour combination were more likely to die.
Gouldian finches mate two to four times a day during breeding season but, given the opportunity, the female will cuckold her mate and go to great lengths to keep it a secret.
Males will help to incubate eggs and feed chicks, unless the female's infidelity becomes known, in which case he might abandon the brood.
''They have a lot to lose if caught with another male so we were intrigued to find out why the female would run such a risk, since the costs of cheating are quite high,'' Dr Griffith said.
The results suggest the birds are driven by the possibility of stronger young. In just one coupling, a genetically superior male could fertilise up to 75 per cent of the female's eggs, the biologists found.
''The female is apparently able to select out genetically good sperm from bad sperm,'' Dr Griffith said. ''It's like a lottery where you rig the lottery.''