Female birds competing for mates resemble males
Female birds can puff out their chests and prance around just like their male counterparts in species where parents share caring for offspring and females need to compete for mates, researchers have found.
Ornithologists at Cornell University say females in species that breed in groups can show characteristics usually associated with males, like bright plumage and courtship dances.
The researchers, whose work was published this week in Nature, focused on African starlings, but say the concept is the same for all birds.
"We've known it happens with females in some specialized cases, but it's probably more widespread than we ever realized before," said Irby Lovette of Cornell in a statement.
These typically male embellishments are the result of sexual selection and are seen in pair-breeding bird species where males court females and females must choose their mates carefully.
In species where males and females share the job of caring for offspring and females have to compete for the attention of males, the two sexes tend to look more alike.
The researchers say this isn't the result of males evolving to be less colourful, but of females evolving to be more ornate.
To test this idea, the scientists compared 17 species of African starlings that breed co-operatively with 28 typical pair-breeding species.
They analyzed the DNA of all 45 species — 1,600 bird specimens in total — to reconstruct the birds' evolutionary history.
They found sexual selection in the pair-breeders pushes the males to become sexual show-offs, and the same force in co-operative breeds pushed females to be just as extravagant.
"This goes beyond starlings," said study co-author Dustin Rubenstein.
"Any species that lives with relatives might be expected to show similar patterns. This type of complex social behaviour is not only common in birds, but also many mammals — including humans — and insects," he said.