Horses sweat, men perspire and ladies glow – but they are not the only creatures to be so refined. Researchers now know that budgies have a sexual radiance all of their own.
A study of budgerigar sex-appeal has found the feathers on the crowns of both sexes emit a fluorescent sparkle that is invisible to humans but is an alluring signal to would-be lovers of the avian world.
Just as companies sometimes use fluorescent lights to draw attention to their advertisements and logos, so the budgie uses fluorescent pigments to show off its feathery head-dress to suitors.
Kathryn Arnold and her colleagues at Glasgow University have demonstrated the importance of fluorescent feathers in a study of the budgie's head-bobbing courtship ritual.
Theywork by absorbing ultraviolet light, invisible to the human eye, and re-emitting it at longer wavelengths that can be seen by budgerigars and other members of the parrot family. "It has been noticed that if you put a parrot under an ultraviolet light it glows," Dr Arnold said.
When the scientists smeared sunblock on the head feathers of an otherwise sexy budgie, the bird became noticeably less attractive to other birds – in effect making it 14 per cent less alluring to the opposite sex than without the sunblock.
The findings, published in the journal Science, are the first experimental evidence showing that animals use fluorescent pigments to attract potential mates. Dr Arnold believes that budgies and other parrots use fluorescence as a way of showing off their general fitness to be a sexual partner. "We know it's a metabolically expensive form of coloration, so it is an honest indicator of individual quality," she said.