As per a new study, sexual selection isn't the last word on bird plumage.
University of Wisconsin-Milwaukee researchers going back to Charles Darwin have focused on the contrast between the sexes, attributing the males' brighter colors to their need to attract mates.
Researchers took a different approach, testing a hypothesis that evolution has actually resulted in similarities among the sexes as much as differences.
Looking at nearly 1,000 species of birds, they found that while males often have brighter feathers than females, the two sexes have come closer together in color over time to blend into their surroundings and hide from predators. Natural selection, that is, during migration, breeding in subtropical locales and care of young, is as powerful as sexual selection.
Although most studies of bird plumage focus on dichromatism, evolutionary change has most often led to similar, rather than different, plumage in males and females, the authors wrote.
Peter Dunn and Linda Whittingham added that the study shows that ecology and behavior are driving the color of both sexes and it is not due to sexual selection.
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When the sexes became more similar in color, they did so for reasons of natural selection. When the color gap increased, it had more to do with sexual selection, they found.
Dunn hopes the findings will send future research in new directions.
The paper appears in Science Advances.