How Animals Keep Warm in Freezing Wetness

We shiver to think of going without heavy coats in snow, but snowshoe hares, gophers and birds look perfectly comfortable. What’s their secret?

The secret is trapping air in feathers and fur, and using material that sheds water. This article on Science Daily explains how air trapped within feathers and fur works as an ideal insulator. It took scientists at MIT to figure out why their coverings work so much better than man-made ones:

To examine how the hair properties (such as hair length and hair spacing) affect the wettability of the surface, the researchers experimented with various parameters including hair length, hair spacing, fluid viscosity and plunging speeds, finding that the geometry of the hairy surface plays a significant role. In particular, the denser the hair array, the more water repellant the surface is.

The team also found the hairy texture entrains a much larger quantity of air than that of the classical dip coating called the Landau-Levich coating, thereby creating an “augmented version” of dip coating. However, unlike classic Landau-Levich, the dominant balance at orders of length relevant to aquatic animal hair is between viscous stresses and hydrostatic pressure. “We hope these findings could also potentially inform advances in coating technology,” said Nasto.

Feathers work extremely well, too. Take an extreme case: penguins. In “The anti-icing trick of penguins,” another article on Science Daily describes several factors in penguin feathers that both resist water and trap air.

Antarctic penguins live in a bitterly cold place, where the air temperature can drop to -40 degrees Celsius and the winds can hurtle at speeds of 40 meters per second. Although these birds routinely hop in and out of the water in sub-freezing temperatures, they manage to keep ice from coating their feathers.

Now researchers have examined penguin feathers in extreme detail and think they know the penguins’ anti-icing trick: a combination of nanostructures and a special oil make Antarctic penguin feathers ultra-water-repelling, or superhydrophobic. Droplets of water on the feathers bead up so much that’s it’s difficult for heat to flow out of the droplet, and the water will roll off before it has time to freeze.

That’s really cool! –er, warm. But it must work just as well for Weddell seals, because they swim in the same waters as the penguins as if they were sport-swimming in the Bahamas.

Needless to say, scientists at UCLA would like to learn these tricks. Ever had to wait for the de-icing operation before a flight?

Penguin’s anti-icing solutions could help humans solve some of our own problems with ice. For example, ice on an airplane’s wings, flaps and rudder can alter the aerodynamic properties of the plane and even cause it to crash. Airlines spend lots of time and money applying chemical de-icers to planes that fly in winter weather. Superhydrophobic surfaces inspired by penguins might be cheaper, longer-lasting and more environmentally friendly.

“It’s a little ironic that a bird that doesn’t fly could one day help airplane fly more safely,” Kavehpour said.

Who taught animals these tricks? When you think about birds and mammals, they endure all the environments Earth throws at them. Arctic terns, for instance, as shown in Illustra’s film Flight, cover almost the whole globe’s temperature gradients. Moreover, they dive into the water at all latitudes to catch their food. Coyotes thrive from deserts to Yellowstone winter snows. The match of each animal’s covering to its habitat is truly astonishing.

Thinking this over, it’s apparent that a lot more design is involved than just producing materials that work. The hairs and feathers need the right length, density, and oil to function properly. They must be layered properly. They must cover the most vulnerable spots. And they have to allow the animal to move. How is that coded for genetically? We see glimpses of hierarchical design not explainable by self-organization or random mutations and selection. But of course; everything in the living world exhibits brilliant design. That’s why biomimetics is so popular.

God didn’t give humans fur or feathers, but He gave them brains to figure things out. The first humans borrowed animal skins, then figured out how to make better and better clothing material. That’s why you can find humans at the North Pole, the South Pole, Death Valley, the Sahara desert, and everything in between. For most temperate environments, human skin works really well at water resistance and evaporative cooling, so we, too, have some pretty amazing material to be thankful for. We could learn a great deal from animals, though, about materials science that is both environmentally friendly and functionally superior to many artificial materials.