Pigs do it. Mice do it. Dogs definitely do it. Kangaroos? Not so much.
Why do animals shake? The short answer is, because they’re wet. But there’s actually more to it than that — a lot more.
In an article published in Journal of the Royal Society Interface, Dr. Andrew Dickerson and others at the Georgia Institute of Technology take a broad look at this odd issue. They wanted to know why it’s so important for animals to dry off, and how they do it so quickly. The research team of biologists and mechanical engineers used high-speed videography and “fur particle tracking” to record the peculiar shaking characteristics of 33 animals, including 16 animals species and five dog breeds.
It turns out that mammals preserve a considerable amount of energy by doing their cute little quaver. If it weren’t for their ability to shake, animals would have to use up to 20 percent of their daily caloric energy simply staying dry.
And nearly all furry mammals shake to rid themselves of water. Those that don’t, like kangaroos who shake only part of their body, tend to live in desert climates where keeping dry isn’t very hard. But not all animals shake at the same rate. Smaller animals seem to shake more quickly — 30 shakes per second for a mouse — while bears, tigers and big dogs average only about four (still twice as fast as your average techno beat).
It may look cute, but an animal’s shake is actually a very violent process — for the water, at least. A drop of water sitting on an animal’s fur is thrown off at accelerations of between 10-70 times gravity. That’s a serious ride! Even the best-trained fighter pilots only endure sustained accelerations of about 9 Gs.
How exactly do animals reach such breakneck speeds? Well, a lot of it has to do with all that extra skin. "Loose mammalian dermal tissue" — the same stuff a mama bear uses to carry her cubs around — helps animals keep dry. By being able to whip their wet and heavy fur around their bodies, certain mammals (again: mice, tigers, dogs, bears) are able to increase both acceleration speeds and surface area. They are remarkably efficient dryers.
In fact, in an interesting find, Dickerson and his team have shown that these animals actually do the job as efficiently as possible. A slower shake would be less efficient, while a faster one would experience diminished returns. The observed shaking frequencies are in each case just about optimal, allowing the animals to rid themselves of about 70 percent of accumulated water in mere seconds.
This should all be impressive to humans. It takes us not seconds but minutes to dry our hair — just over three on average. An amount of blow-drying that sucks up between 60 and 90 watts of electricity. Granted, in the grand scheme, that’s not all that much energy, but it’s a lot more than your dog needs.
Mother Nature wins again!