Birds feathers inspire future water-capture technologies

The desert-dwelling sandgrouse. Image: Dhaval Vargiya

Feathers from a bird with an incredible ability to retain water could inspire the next generation of water capture technology, say US researchers.

Many birds’ feathers are remarkably efficient at shedding water — hence the phrase “water off a duck’s back”. Much more unusual are the belly feathers of the sandgrouse.

Using high resolution microscopes and 3D technology, scientists at Johns Hopkins University and Massachusetts Institute of Technology have been studying the feathers of the desert-dwelling sandgrouse, and revealing for the first time how they hold so much water.

Desert sandgrouse, such as the namaqua, nest up to 30km away from watering holes. Adult male desert sandgrouse have specially adapted feathers on their bellies that hold water, even during flight, allowing the birds to transport water back to their chicks.

Out of evolutionary necessity, the sandgrouse developed a clever way to carry the water, by storing it in its plumes. It walks into shallow water, fluffs its feathers and rocks back and forth.

This action means it can soak up to 25ml of water - an incredible 15% of its body weight - while still being able to fly at speeds of up to 65km per hour. When it returns to its young, the chicks suck the water directly from the feathers with their beaks.

"There are a lot of parameters to play with, which creates a lot of complexity but also a lot of opportunity in creating such microstructures."

Jochen Mueller, John Hopkins University

This system is unique to the sandgrouse and its subspecies in other parts of the world. Naturally, most birds have water-repellent feathers.

“Birds don’t want to get wet and heavy because that limits their flying capabilities,” explains Jochen Mueller, the study’s co-author and an assistant professor in the department of civil and systems engineering at Johns Hopkins University.

"There are a lot of parameters to play with, which creates a lot of complexity but also a lot of opportunity in creating such microstructures," he added.

The microscopy techniques used in the new study allowed the dimensions of the different parts of the feather to be measured.

The engineers used various 2D and 3D microscopes to view feathers, donated by the Harvard Museum of Comparative Zoology and the Los Angeles Natural History Museum, from stuffed sandgrouses that lived long ago, and other birds for comparison.

They saw that as feathers enter water, microscopic coiled structures within automatically suck up the fluid using capillary action through tiny tubes. The water spreads throughout the feather, and the wet tubes uncoil and expand, absorbing water like a sponge, while those on the tip of the feather remain dry and coiled.

That surface layer acts almost like a bottle cap, retaining the trapped moisture within.

The findings could be used in biomimicry for future engineering designs that require controlled liquid intake, retention and release. Possible applications include the design of netting for collecting and retaining water from fog and dew in desert regions.