How a dumpy, short-legged bird could change water bottle designs

The sandgrouse’s unique feathers can hold and transport fluids.
Pin-tailed sandgrouse in a body of water
Pin-tailed sandgrouse hovering in a watering hole. DEPOSIT PHOTOS

The sandgrouse isn’t considered an elegant-looking bird. In fact, it is described by online database ebird as a “dumpy, short-legged, pigeon-like bird that shuffles awkwardly on the ground.” But it also harbors a special secret: It can carry water weighing around 15 percent of its body weight over short flights. Short in this case is up to 20 miles—enough to travel from a watering hole back to their nest. The key to this ability is the architecture of their belly feathers. 

In a new study published this week in the journal Royal Society Interface, researchers used high-tech microscopes and 3D technology to reveal the detailed design of these feathers, with hopes that it might inspire future engineers to create better water bottles, or sports hydration packs. According to a press release, the team says that they plan to “print similar structures [as the bird feathers] in 3D and pursue commercial applications.”

To observe how the feathers performed their water-toting magic, the researchers examined specimens they got from natural history museums and looked at dry feathers up close using light microscopy, scanning electron microscopy, and micro-CT. They then dunked them in water, and repeated the process. 

[Related: Cuttlefish have amazing eyes, so robot-makers are copying them]

What they saw was that the feathers themselves were made up of a mesh of barbs, tubes, grooves, hooks, and helical coils, with components that could bend, curl, cluster together, and more when wetted. In other words, they were optimized for holding and retaining water.

Close up of sandgrouse feathers. Johns Hopkins University

“The microscopy techniques used in the new study allowed the dimensions of the different parts of the feather to be measured,” according to the press release. “In the inner zone, the barb shafts are large and stiff enough to provide a rigid base about which the other parts of the feather deform, and the barbules are small and flexible enough that surface tension is sufficient to bend the straight extensions into tear-like structures that hold water. And in the outer zone, the barb shafts and barbules are smaller still, allowing them to curl around the inner zone, further retaining water.”

Further, the team also used measurements of dimensions of the feather components to make computer models of them. They also used these numbers to calculate factors like surface tension force and the stiffness of the components that bend. 

“To see that level of detail…This is what we need to understand in order to use those principles to create new materials,” Jochen Mueller, an assistant professor in Johns Hopkins’ Department of Civil and Systems Engineering and an author on the paper, said in a press release

One use of this design would be to make water bottles that don’t allow the water to slosh around. Another possible application is to incorporate bits of this structure into netting in desert areas to capture and collect water from fog and dew.