Women cheat on men for their own needs but superb starling females stray from their mates for the sake of their chicks, according to recent Cornell research. This reasoning includes being able to know if mates are too 'genetically similar' for breeding.

That gives 'doing it for the kids' a whole new layer of meaning. The study found that superb starling females (Lamprotornis superbus) cheat on their mates based on these factors:
  • Superb starlings are cooperative breeders, meaning breeding pairs get help in raising chicks from other family group members. Some females mate with subordinate males when they need help to raise their chicks. This additional male then acquires food and tends to the nestlings, which increases the chicks' survival rates.
  • The subordinate males get something from this also. Females often leave the group when young but most males live their entire lives with their families and, therefore, are usually related to the chicks. By helping the chicks survive, they pass on familial genes.
  • Because family males are often around their entire lives, some females cheat with males outside their group if they sense their mates are too genetically similar to themselves. Mating with strangers increases their brood's genetic diversity even though it does not give them additional help.

How do they know? No one is sure how females detect the genetic similarities between themselves and their mates, though other species of birds appear to adopt similar mating strategies.

Usually, if a female bird (or 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. Not so with these starlings.

Superb starlings of East Africa are cooperative breeders and even if the female is caught cheating, she still may get help from other group members. Still, superb starlings tend to stray much less often than other cooperative breeders, despite the dual potential benefits for females in seeking extra-pair mates.

"In most avian cooperative breeders, 40 to 60 percent of offspring are a result of extra-pair matings, but in superb starlings, only about 14 percent of the offspring are fathered by other males," said Rubenstein. No one knows why superb starling females have lower rates of cheating, but Rubenstein said it suggests that there may be less conflict between the sexes than in other species. He is currently researching this issue.

While it has long been known that males of many species cheat and mate widely to produce as many offspring as possible to spread their genes, the reasons behind female infidelity appear more complex. With this study and this species, "we can break down the reasons why superb starling females are not faithful to their mates and see that they have different extra-pair mating strategies," said Rubenstein. "It adds a whole new layer of complexity to the story."

Source: Cornell