Male desert-dwelling sandgrouses have a truly extraordinary ability to gather water in their specially-adapted belly feathers, hold and safely transport it during flight and release it to their chicks back at the nest.
Now, engineers have taken an extremely close look at these special feathers to finally reveal exactly how they can hold so much water.
The feather’s unique architecture, described in The Royal Society Interface, could inspire the next generation of absorbent materials.
“It’s super fascinating to see how nature managed to create structures so perfectly efficient to take in and hold water,” says co-author Jochen Mueller, an Assistant Professor in the Department of Civil and Systems Engineering at Johns Hopkin University in the US.
“From an engineering perspective, we think the findings could lead to new bio-inspired creations.”
Sandgrouse (Pteroclidae) are a family of sixteen species of ground-dwelling birds found in Asian and African deserts.
African sandgrouse need to nest as far as 32 kilometres away from watering holes, to stay safe from predators, and the male sandgrouse’s ability to absorb and retain water in his feathers keeps most of it safe over the roughly half hour flight.
Engineers zeroed in on the microstructures of the belly feathers from a single male adult Namaqua sandgrouse (Pterocles namaqua) using scanning electron microscopy, microcomputed tomography (which uses x-rays to produce 3D images), light microscopy, and 3D videography.
They observed the feathers while dry, wet, and then, in an imitation of a sandgrouse at a watering hole, while dry feathers were dunked in water, pulled out, and then resubmerged.
“When you do that type of work, you can’t even breathe or else you blow it away,” says Mueller.
They found that the shafts of the feathers are just a fraction of the width of a human hair and contain even tinier individual barbules – coiled hairlike extensions on the feather that expand to soak up water like a sponge.
The feather’s structure is optimised to hold and retain water in a few different ways. For instance, curled barbules near the top of the feather act almost like caps to keep water held in the forest of barbules close to the shaft. This is possible thanks to tubular structures on the barbules that capture water, and the way that the barbules form protective tentlike clusters when wet.
“That’s what excited us, to see that level of detail,” says Mueller, who specialises in smart materials and design.
“This is what we need to understand in order to use those principles to create new materials.”
These findings will underpin the designs of new materials for the controlled absorption, secure retention, and easy release of liquids. Potential future applications include netting for collecting water from frog and dew in desert regions, medical swabs that efficiently soak up liquids and easily release it, and even a water bottle designed to prevent annoying swinging and sloshing.
Mueller is contemplating a design that includes an inner feather-like system that keeps water from sloshing around while someone moves with it, such as a hydration pack or water bladder for runners.