Male purple-crowned fairy-wrens use their purple plumage to display their social status and competitive ability, according to a study by Monash University biologists including ARC Future Fellow and Discovery Projects recipient, Associate Professor Anne Peters. The study showed that the function of bright plumage in attracting mates or repelling rivals may be gained or lost independently, offering some new explanations for the great diversity of brightly coloured plumages seen in birds.

While some male birds seasonally produce a brightly coloured nuptial plumage to attract females at the start of the breeding season, the researchers studying the monogamous purple-crowned fairy-wren found that, as well as being faithful long-term to their partners, these birds also act aggressively towards other rival males. By closely following marked individuals over six years and watching their behaviour around 3D lifelike male models, the researchers established that ‘prettier’ versions of such models—males with more developed purple crowns—were attacked more aggressively by the dominant male in family groups.

The study has provided new insights into the function of plumage ornaments, and how they are gained or lost through different evolutionary processes. The long term research also aims to make a contribution to the conservation of this endangered species.

The research is significant because it is the first time that researchers have found evidence for such evolutionary scenarios, and it shows how complex—even more than previously thought—the evolution of colourful plumage ornaments might be.

Image: Resident breeder male purple-crowned fairy-wren investigating a 3D-printed model representing a male intruder in nuptial plumage in his territory.
Credit: Laurent Lermusiaux/AWC.