Why female birds cheat on their partners

Female birds may be socially connected to one male for its entire life, but they are not always faithful to the same mate.

Washington: Female birds may be socially connected to one male for its entire life, but they are not always faithful to the same mate.
In some cases, scientists have found that up to 70 percent of the eggs found in some nests were fertilized by a male other than the primary occupant, protector, and supplier of the nest, the ABC News reported.

This provides two advantages: greater genetic diversity in her chicks, and thus more resistance to disease, and yet the man of the nest will remain around to help raise the brood, probably unaware that some of the chicks aren`t his.

In a study published in the journal Molecular Ecology, researchers from the University of East Anglia found that female Seychelles warblers prefer having their eggs fertilized by a male other than their social partner.

They captured more than 97 percent of the warblers on the tiny island of Cousin in the Seychelles and drew DNA samples from the birds and observed their breeding habits.

Then they monitored the fate of 160 birds that hatched between 1997 and 1999 for 10 years and found that 40 percent of the offspring were fertilized by males other than the female`s mate.

And most important, these birds had higher genetic diversity of disease detecting genes-meaning they were more likely to defeat more diseases-than "if they had been sired by the cuckolded male," the scientists said.

Another study, from the University of Melbourne in Australia and the University of Groningen in the Netherlands, found that "extra pair offspring," as scientists now call birds sired by an outsider, have advantages other than just genetic diversity.

These researchers collected 1,732 eggs from 190 blue tit nests to determine their hatching order. All chicks were tested to identify the father.

It turns out that mom gave her illicit chicks a better start in life by hatching the outsider`s eggs earlier than her own mate`s eggs. That made them stronger than the competition during those crucial early days, and that could give them an advantage for the rest of their lives, the researchers concluded.

Michael Magrath of the University of Melbourne said that almost 75 percent of the offspring that resulted from these extra pair matings were produced in the first half of the clutch, giving them a 10 hour head start on life.