Buzz
Stefan Pociask:
The timeless mystery of bats hanging upside down. It's certainly strange that a mammal—an animal at that—spends its time in this inverted position. Sure, some monkeys do it when they're just being playful. A few other tree-dwelling creatures, such as margay cats, may hang upside down to reach something or even hunt while doing so... But bats stand alone as creatures that spend a significant portion of their lives in this upside-down posture: feeding, nurturing their young, and yes, even sleeping or roosting in this way.
There's a practical and logical reason behind this odd behavior: Bats must hang upside down in order to take flight.
First, it's important to note that bats are neither birds nor insects. These are the other two groups of animals that are capable of true powered flight (as opposed to gliding). The key difference between bat flight and that of birds or insects is their weight—specifically, the balance between their weight and the lift capacity of their wings. When you approach a bird or an insect, most species can fly straight up from a standstill, and they do it quickly.
Bats, on the other hand (or wing), struggle with this. They find it challenging to take off from the ground (though they can do it, it’s just harder). Insects and birds often take a leap into the air to help them get started in the right direction, and then their powerful wings take over, lifting them higher and higher.
Birds have hollow bones, but bats do not. Insects have lightweight chitin or soft, airy tissue, unlike bats. Bats also don’t have what you’d call 'powerful' wings. These remarkable creatures are mammals, the only mammals capable of flight. To evolve a flying mammal, nature had to make some compromises. Once airborne, bats manage quite well in the air, easily flying circles around most birds. The real challenge is simply getting off the ground.
To overcome the extra weight that mammals naturally have and to solve the problem of getting off the ground, evolution devised another solution for bats. The idea was simple: 'What if we drop them from above? That way, they’re already in the air and just need to start flapping.'
It turned out to be a brilliant solution. However, bat feet aren’t designed for perching on a branch. As mammals, their muscles, bones, and tendons are set up quite differently from those of birds. When a bird lands on a branch, their tendons automatically lock their toes into a firmer grip, which helps them stay on the perch. This is an instinctive trait for birds, and it’s universal. That’s why they don't fall off while sleeping.
Bats, being mammals, are structurally different from other flying creatures. To adapt to this, nature came up with a clever solution: 'What if they hung upside down?' This way, their tendons would naturally close their toes, much like a bird’s feet lock in place when perched, but in reverse. So, evolution granted bats the ability to hang from an object, and when they let go, they are instantly airborne. Thanks to gravity assisting their takeoff, bats can achieve flight even more quickly than birds, who have to overcome gravity.
Just a quick note: If you’ve ever wondered how bats manage to relieve themselves while hanging upside down... First, their poop isn’t a problem. Bat droppings resemble tiny rice grains, and when they hang, it simply falls to the floor of their roosting place as guano. As for pee, bats handle that too—they simply hold it in until they are flying.
So there you have it. Bats sleep upside down because, as mammals, they can’t take flight as easily as birds. But when they hang, all they need to do is let go and they’re flying.
Makes perfect sense, right?
That being said, not all of the 1240+ bat species hang upside down. There are some exceptions—around six species from two different families. One is found in South America (Thyropteridae) and the other in Madagascar (Myzopodidae). The Myzopodidae family, which includes just a single species, is extremely rare.
It turns out that these bats roost inside the tubes of young, unfurled banana leaves and other similarly large leaves. When they cling to the inside of the rolled-up leaf, they do so with their heads facing upward. The issue with living in rolled leaves is that, as the days pass, the leaves continue to grow and eventually unfurl. Each time this happens, the entire group of bats has to relocate to a new spot. This process repeats itself over and over. All six species of these rare bats have suction cups on each wrist and ankle, which they use to attach to the smooth inner surface of the leaf tube. Evolution: the more you uncover, the more astonishing it is.
This post originally appeared on Quora. Click here to view.
