Melbourne, May 13 (ANI): Female tit birds are known for mating with rival males before their social partner, for giving genetic advantage to their chicks. But, a new study has questioned this belief by claiming that the chicks resulted from promiscuity are benefited only because they are laid and hatch earlier.

Dutch and Australian researchers have claimed that the chicks are stronger, larger, and more likely to survive simply because they get a head start over chicks produced from faithful unions.

Dr. Michael Magrath, of the University of Melbourne’s Department of Zoology, says that this means they begin feeding earlier than their half-siblings, who may hatch as much as five days later.

For the study, the researchers numbered 1732 eggs from 190 blue tit bird nests in the order in which they were laid across two breeding seasons, and then placed the eggs in an incubator to note the order in which they hatched, before finally returning them to their original nest.

“Remarkably, almost 75 per cent of the offspring from these ‘extra-pair’ matings were produced in the first half of the clutch,” ABC News quoted him as saying.

On an average, the extra-pair chicks were hatched 10 hours before their half-siblings, which gave them time to gain an initial size advantage because they start feeding immediately.

The promiscuous nature of commonly monogamous female birds has puzzled researchers, but studies had earlier showed that the offspring of these so-called extra-pair matings were bigger, had better immune response, and were more likely to survive.

Thus, the researchers had concluded that these matings provided a genetic advantage.

“We don’t rule out the idea (extra-pair mating) is to gain a genetic advantage. But we have shown what’s been considered good evidence isn’t that strong,” said Magrath.

The study has been published online in Current Biology. (ANI)