New research shows that the woodcock is the unlikely owner of the brightest of white feathers of any bird tested.
Woodcocks are not known for their white plumage. Their upper surface of these nocturnal waders is a mosaic of browns and greys that camouflages them exquisitely against forest floors by day.
“That’s the beauty of it,” says Jamie Dunning, who led the work at Imperial College London. “They keep it where you can’t see it, but where they can get it out when they need it.”
The research, published in Royal Society Interface, focused on a fringe of white spots on the underside tips of the tail feathers of both males and females.
It shows that these are 30 per cent brighter than any other plumage tested to date. The feathers’ barbs contain microscopic reflective structures and are flattened and overlapping, like Venetian blinds, to maximise the reflective surface area. The angle at which they overlap enables the birds to direct the signal precisely.
The feathers’ brightness probably aids visual communication in low-light environments, says Dunning. But what are they signalling? And to whom?
Woodcock are well known for the males’ “roding” flights performed for females on the ground. “We know females use it to signal to males roding above them,” says Dunning. “And we think maybe the roding males use it too, because they fan their tail feathers as they do their parachuting flight down.”
“We turned up an old, obscure reference to French hunters making fans out of the tail feathers and flashing them in the woods to attract woodcock,” says Dunning. “There’s another record of a female possibly flashing her tail feathers to a line of chicks following her.”
They may also use it to startle predators. “If you catch woodcock in a net to ring them, they frantically flash their tail feathers at you as you approach.
“It’s probably a bit of a multi-tool,” says Dunning. “And they can put it back in their bag when they’re finished with it.”
Main image: A woodcock flashes the white spots on the underside of its tail feather tips. © Sven-Erik Arndt/Arterra/Universal Images Group/Getty Images