Why cats land on their feet - the well-balanced cat explained
Cats are agile and graceful; as perfectly at home walking on the top of a narrow garden fence as when sauntering down the garden path. They can climb up trees (though climbing down is sometimes an issue) and walk along the branches with nonchalant ease. As the video further down this article demonstrates, walking the tightrope is no challenge for a well-balanced cat. So how do they do it?
Thereís no one secret ingredient, but the most important factor can be found just behind the catís ears - in the semicircular canals of the inner ear. Not only cats have these canals, all mammals do. But thatís like saying humans have a sense of smell and so do bloodhounds. Bloodhounds use their noses better, and cats make the most of their semi-circular canals. So what is a semi-circular canal and how does it help balance?
Well, the world is three-dimensional, so the inner ear has three of those structures, set pretty much at the right angles to each other. To get technical for a moment, these canals are: the horizontal, anterior and posterior canals. The canals are filled with fluid, and when this fluid shifts about, this alerts the brain that the balance of the body has shifted. So, for example when a cat moves her head from side to side, the fluid presses on the cupula (a sensory structure in the ear which nature has designed for this purpose). Hair cells within the cupula pick up on the mechanical movement of the fluid and send electrical signals to the brain.
Movement of the fluid in each of the canals picks up on different directions. The horizontal semicircular canal alerts the brain about the rotation of the head around the vertical axis (as for example when doing a pirouette). The anterior and posterior semicircular canals are positioned at approximately 45 degrees between two anatomical points called the sagittal plane and the frontal plane. What this means is that when a cat moves her head up and down in a nodding movement, the movement is recorded in the sagittal plane. When the head moves from side to side it registers on the frontal plane. So whatever direction the head moves, the semicircular canals are busy telling the catís brain which way it is moving and how far and how fast.
Now letís put this anatomy lesson into practice. The cat has rolled over once too often, and tumbled off the top of the wardrobe. Letís see what happens as she falls to the floor. In the first moments of falling, the catís sensory equipment immediately works out which way is up, and the cat quickly rotates her head so it is upwards.
The movement of the head informs the brain which signals to send to other parts of the body to get everything turned into place, because once the head is aligned with the horizontal plane, the rest of the cat can now swiftly whip into place to align with the head. So while still in mid-air the cat is in position, and so is the landing gear. The cat lands on her feet, with the stronger back legs slightly lower to take most of the weight. Because each twist of the head has informed the brain exactly how to restore the catís balance, a perfect landing is guaranteed even in pitch dark conditions.
The whole thing works as a reflex action so it takes milliseconds for the feline body to be properly aligned. So why, if all mammals use their semicircular canals for balance, do cats handle falling so much better than we humans do? Itís because cats have other anatomical advantages.
For a start this is an animal which can wash almost every part of its body with its tongue. To achieve this takes a spine as flexible as an elastic band, and muscles and reflexes that can snap the limbs instantly into place. Even an olympic gymnast canít compete with a cat, because cats lack a true collarbone; so their bodies rotate more easily in mid-air than any other mammal. (The same lack of a proper collarbone helps cats squeeze through gaps that youíd think a kitten couldnít get through.)
And then there is the catís not-so-secret weapon; her tail. If you watch a cat walking along a narrow edge, you will see the tail swing from side to side in time with each pace. This is because the cat is using her tail as a counterweight to compensate for changes in weight distribution. Observe that the tail always moves in the opposite direction to the head, in this way preserving the equilibrium of the body overall. Now watch as the cat prepares to jump off the fence. She raises her tail straight up. This helps to arrest forward movement following the jump and makes for a more controlled landing.
Although the tail is helpful to maintain balance, a cat can manage without it. Indeed, cats which do not have tails, such as that well-known tail-less cat breed - the Manx, are still pretty good at balancing. Even cats which have lost their tail through injury can quickly adjust.
But a good comparison is with a tightrope walker. A tightrope walker uses a pole as a counterbalance in just the same way as a cat uses her tail. Although some very good tightrope walkers dispense with the pole altogether, that doesnít mean that the pole would not make the job easier. Interestingly Manx cats have longer hind legs than front legs and the hind legs are very muscular and therefore heavier. This shifts more weight into the rear of the cat and may to some extent compensate for the lack of tail. To put it crudely, Manx cats balance with their butts.
Cats have one more anatomical feature which puts them ahead of tightrope walkers - their paws. When the cat walks, her front paws turn somewhat inward. As you can tell by seeing a catís paw-prints in the snow, the front legs are directly in line. The back paws turn inwards somewhat less but still take up very little width. Even on the ground, cats walk as if they were on a tightrope. So it hardly matters if a cat is walking along the top of the narrow fence if that fence is no narrower than the space the cat needs for normal perambulation.
And finally, of course, the cat has a backup feature that no tightrope walker possesses. If something does go wrong, the tightrope walker canít instantly shoot sixteen hooked claws into the rope to keep him there while his semi-circular canals do their stuff to get his balance back. Cats have so many unfair advantages.