New video of male riflebirds’ extreme wrist flares and feather noises reveals how these show-offs do their dazzle.
Males of the four Ptiloris species, a group within the birds of paradise native to Australia and New Guinea, have long fascinated biologists as well as female birds with their courtship displays. A male repeatedly fans out dark satiny wing feathers into a curved arc. He sways his head rhythmically and opens his mouth to a soundtrack of short, sharp thwacking sounds.
How males created the loud percussion was a mystery to science, says Thomas MacGillavry, a zoologist at the University of Veterinary Medicine in Vienna. Researchers at first thought birds somehow clapped their wings together. This makes sound effects in some other bird species. A riflebird instead uses his beak to play his feathers like an instrument, MacGillavry and colleagues conclude in the September issue of the Biological Journal of the Linnean Society.
The team managed to get some new film of a male Victoria’s riflebird (Ptiloris victoriae) in action and examine specimens of other species. As a male swings his head, he periodically closes his beak, briefly hiding the lovely yellow throat lining. The beak whacks against fanned out feathers as it swings over them, like a stick dragged against a picket fence.
That arc of feathers that the beak drums against is a marvel in itself. It curves strikingly inward, like a cape curling forward. To create such a curve takes an extremely flexible wrist.
“In riflebirds, it looks like the males are doing something analogous to a body builder flexing,” MacGillavry says. Yet the birds’ elbow-equivalents are tucked under other tissue, and it’s actually the wrist that bends so much.
The wrist of a dead Victoria’s riflebird specimen could be flexed 237.1 degrees. Other Ptiloris wing specimens bent a few more degrees. That’s “something no other birds can do,” says MacGillavry. At least, as far as we know.