One of the really neat things about diving deep into a scientific problem is that you start to spot surprising things in images or videos that nobody else would see! My book on Falling Felines and Fundamental Physics got me really involved in studying videos of cats landing on their feet after a fall, and after the book came out I wrote a whole blog post about a cat flip video that I happened to see online where I spotted some really neat new dynamics in the falling felines problem.

Well, today I again spotted something remarkable in a falling animal video, and in fact I think it answered a question that I had been unable to answer ever since writing the book!

Let me give a little background: cats possess this remarkable reflex, often called the cat-righting reflex or just the cat flip, that allows them to change the orientation of their body in the air and land on their feet whenever they fall from a height. It is a true reflex, and something that comes naturally to them, and they can do it very fast — they can often land on their feet even if dropped from a height of one foot.

Clearly, cats have developed this instinct because they are natural climbers, and inevitably some of them fall from trees. Evolution has “trained” them to possess this reflex so that they can land safely. Even cats falling from skyscrapers at heights of 20 stories or more often survive with only minor injuries.

So it is easy to understand why a cat has developed this ability… but it turns out that rabbits can also do it! I found this gif on the internet that demonstrates the abilities of rabbits, cats, and dogs (source unknown, alas). It is quite clear that cats and rabbits have little problem landing on their feet, while the poor dog has a lot more trouble.

In the 1960s, one researcher on the righting reflex used rabbits instead of cats, as their capabilities are so strikingly similar.

The rabbit’s ability poses a bit of a puzzle, though: why would rabbits have developed a righting reflex? To the best of my knowledge, rabbits don’t spend a lot of time up in trees. I’ve mentioned this puzzle a number of times while giving talks on the cat-righting reflex. I made two guesses, both of which were a bit unsatisfying. The first guess is that rabbits, while fleeing from ground-based predators, occasionally run right off of ridges or small cliffs, and the reflex helps them land safely. The second guess is that rabbits, when picked up by aerial predators, wriggle themselves free often enough that the ability to land from a height became an important evolutionary selection process.

Well, thanks to the video I’ll show you, I think I’ve found the answer, and it’s different from my guesses!

The video in question is taken from my friend Standplaats Krakow’s Twitter page, where he shares neat memes and videos he find around the internet. (He also does so because he is in poor health and needs financial support to carry on, so if you feel inclined to help here’s his Twitter page with Paypal link.)

The video is of a rabbit (or a hare; I have no idea the difference, as I am a physicist) managing to dodge a swooping bird of prey with some fancy maneuvers:

(I was unable to track down the source of this particular video, so if anyone recognizes it and can point me to it, I will share the attribution.)

The bird swoops in horizontally, and just before it strikes, the rabbit jumps straight up! The bird attempts to reach up with its claws to grab the rabbit, making the animal tumble, but it uses its righting reflex to flip right-side up. By the time it hits the ground, it is already running, leaving a rather irked and unbalanced bird behind.

Watching this video, I became convinced that it revealed the answer to the rabbit-righting puzzle: rabbits leap into the air as a deliberate strategy to avoid avian predators, and the righting reflex allows them to land running! I had assumed that any falls they experienced, like a cat, must be unintentional, but the video shows the opposite.

The strategy is quite brilliant to me. If the rabbit tried to dodge one way or the other while running, the much faster bird could adjust to catch it. The rabbit instead goes in the one direction the bird cannot easily move: straight up! Evolution eventually selected for those rabbits that possess the reflex to land on their feet.

A quick search of YouTube provided other examples of bunnies leaping over swooping birds. I feel pretty confident that this answers the question, “why does a rabbit have a righting reflex?” And I am delighted that the answer was not what I expected!

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Postscript: while I’m thinking of evolutionary strategies for animals to survive falls, I like to point out there are two ways to do it. One way it the cat/rabbit strategy, of developing a magnificently precise righting reflex that has intrigued scientists for centuries. The other way is the panda strategy: just be round and gooshy!