An up-close look at the belly feathers of a desert bird reveals complex coiled structures that absorb and trap water, allowing Namaqua sandgrouse to transport water inside their plumage.
Male Namaqua sandgrouse (Pterocles namaqua) make daily trips to watering holes in South Africa, where they soak their lower feathers in water. The water-logged birds then fly up to 30 kilometres to their thirsty young, which suck water from their father’s feathers. Researchers first discovered that these feathers had coiled filaments called barbules more than 50 years ago. But no one had taken a closer look.
Advertisement
To see the special feathers in detail, researchers used imaging techniques such as high-resolution microscopes, micro-CT scans and 3D modelling technology. They found a stiff central feather shaft supporting symmetrical rows of straight barbs, which were covered in coiled barbules – the entire structure resembling a fern with curly leaves. When they dunked the feathers in water, they watched the flexible, curly barbules draw in water through capillary action.
“Once the barbules get wet, they uncoil and build this kind of dense forest of these now straight barbules, and that’s really what holds the water inside the feather,” says at Johns Hopkins University in Maryland. “The cool thing is that it’s reversible. As soon as the water is out and the feathers dry, they go back into their coiled form.”
Based on earlier reports, Mueller expected these curly barbules on the feather’s barbs, but they also found them sprouting directly from the feather’s central shaft. He and his colleagues also discovered a honeycomb-like structure inside the central feather shaft, which provides lightweight and rigid support.
“Some of the most exciting science comes when new tools are applied to biological systems that have been described for a long time, and the belly feathers of sandgrouse are a prime example of this,” says at the Natural History Museum of Los Angeles County in California, who wasn’t involved in the work.
Mueller hopes a better understanding of sandgrouse feathers could lead to new engineering innovations like nasal swabs to test for COVID-19, which need to both absorb and release liquid efficiently.
The Royal Society Interface
