First Author

Many male birds sport brightly coloured feathers and other ornaments in order to woo as many females as possible. By contrast, females, which tend to focus their efforts on raising their brood, are often unarguably drab. This is because females in most avian species are left on their own to raise their young and face little competition for mates. However, in some species males and females live together in family groups that share breeding responsibilities. This means that fewer females get to mate, so they too have to compete. Dustin Rubenstein of Columbia University in New York City and Irby Lovette of the Cornell Laboratory of Ornithology in Ithaca studied 45 species of African starling to examine the evolutionary consequences of such competition (see page 786). Rubenstein tells Nature more.

How did you come to this question?

I have been studying African starlings for about 10 years, and one species particularly intensely. In this species, the superb starling, birds live in family groups of 20–30 individuals. I have always wondered what the evolutionary causes are of family living in animals, particularly in creatures such as starlings, where some species live in groups and others do not. About six years ago, we started to build an evolutionary tree of Earth's 117 starling species in an effort to find an answer. We collected data from living species in Kenya, museums and zoos.

How did you use the data?

In 2007, we published a study showing that starling species that live in family groups are more likely to live in environmentally unpredictable habitats. Having family members available to raise young might help to buffer the tough conditions.

What about the current study?

This study addresses a different question: what are the evolutionary consequences of living in a group? We found that female starlings living with relatives are just as ornamented as males. Both have traits such as exaggerated crests and tails, or iridescent patches of blue or green feathers. Thus, for species living in family groups, selection for such traits acts with similar intensities on both genders. In species in which individuals don't live with relatives, selection acts less strongly on females.

Do the findings apply only to birds?

We think they may apply to any species in which individuals live with relatives, including many mammals and insects. I often get asked whether that includes humans, and although it may, I prefer to leave figuring that out to the sociologists.