Why Do Females Cheat?

She may not love you anymore or she may feel neglected or experience curiosity. But female cheating is not only limited to humans. In the case of the superb starling, females seem to cheat their males for the sake of their chicks, as Cornell researchers have found.

The superb starling females (Lamprotornis superbus) can mate with subordinate males from within their social group as these individuals can help raise their chicks. (These birds are cooperative breeders, breeding pairs being helped in raising chicks from other individuals within the social group). The supplementary male brings food to the nestlings and protects them, rising the chicks' survival rates.

Usually, females leave the group when they get mature, while most males remain for life with their families, being related with the "husband" and its chicks. As nurses, they enhance in fact their own genes.

Some females cheat with males from another group if they sense the males of their won group are too genetically similar. Strangers can introduce new genes into the brood, even if they do not help in raising the chicks. More diversified genes means healthier offspring. But how females track the genetic similarities, phenomenon also found in other species, is unknown.

"This is the first study to show that individuals from the same population mate with extra-pair males and gain both direct (like additional helpers) and indirect benefits (like better genes for the offspring), but that they do so in different contexts," said Dustin Rubenstein, a former Cornell graduate student in neurobiology and behavior and now a research associate at the Cornell Laboratory of Ornithology and a Miller Research Fellow at the University of California-Berkeley.

"Usually, if a female bird (and at times if a human female) is caught cheating, the partner punishes her by doing less work in raising the chicks, or in extreme cases, leaves her to raise the chicks on her own. But because superb starlings, a bird common to East Africa, are cooperative breeders, females have more incentive to stray, because even if she is caught cheating, she still may get help from other group members. Yet, superb starlings tend to stray much less often than other cooperative breeders, despite the dual potential benefits for females in seeking extra-pair mates." said Rubenstein. "In most avian cooperative breeders, 40 to 60 % of offspring are a result of extra-pair matings, but in superb starlings, only about 14 % of the offspring are fathered by other males," Rubenstein also stated.

Rubenstein explains it by a less powerful war of the sexes in the case of this species, compared to others.