A new study has revealed that mother birds can provide an early advantage to the chicks that they have sired with their non-social partner (known as extra-pair offspring).
It has long been known that female birds commonly mate with males other than their social partner, producing broods of mixed paternity in which the interloper's 'extra pair' offspring often outperform their half brothers and sisters.
While the superiority of these extra-pair offspring has generally been attributed to improved genetics, the new study has revealed that the difference may have more to do with mothers giving these 'extra pair' offspring a head start.
The team from the Universities of Melbourne and Groningen in the Netherlands have found that the superior performance of these extra-pair young arises largely because they are placed earlier in the laying order.
"Our findings indicate that mothers often give extra-pair offspring a better start in life, which can have life-long benefits" said Dr Michael Magrath from the Department of Zoology at the University of Melbourne.
"Our study examined a population of blue tits which are usually socially monogamous, but females commonly mate outside their pair to produce clutches with mixed parentage. Remarkably, almost 75% of the offspring that resulted from these 'extra pair' matings were produced in the first half of the clutch."
The study will be published in the latest issue of Current Biology on May 12.
Over two breeding seasons, Dr Magrath and colleagues numbered all 1732 eggs from 190 blue tit nests to determine their laying order. They placed these eggs in incubators to determine hatching order and, as they hatched, brought the chicks back to their original nests to monitor survival and growth. All chicks were also genotyped in order to determine the offspring's sex and genetic father.
"Typically, the eggs in a clutch hatch over a period of several d
|Contact: Nerissa Hannink|
University of Melbourne