What would a dog or cat be without their tail? It is hard to imagine a dog without it being able to wag its tail in excitement or a cat without it showing off its tail as it dominates your home. Of course, it’s more than just cats and dogs – from Lions, Panthers, and Bears (oh my!) to Ravens and Dolphins and even a few animals not represented by an NFL team, tails are common throughout the animal kingdom. There are many reasons for tails’ existence, ranging from balance to the added navigation ability they can give flying and swimming animals to more decorative examples such as a peacock’s tail being used to attract mates.
But what about bats? The interesting thing about bats is that, while most bats do indeed have tails, a few don’t. What’s more, the purpose of tails in those who do have it can be unclear. With that in mind, let’s wrap up the “tail end” of this intro on bat tails and see what’s at the heart of the question.
An Overview of Bats and Tails
There are around 1,300 kinds of bats in the world, and most of them have tails. The big differentiation for most variations is whether the tails are free of or encased within what is known as the uropatagium, which is the thin membrane of skin between bats’ thighs. Those whose tails are free of the membrane are known as free-tailed bats. In these bats, the tail tends to extend far beyond this membrane of skin and is very visible, whereas in bats where the tail is instead encased within the uropatagium, it tends to be a lot less noticeable. Among the bats with free tails are molossids and rhinopomatids, while vespertilionids tend to align more with the bats whose tails are mostly tucked away within or only barely extend beyond their uropatagium.
How Bats Use Their Tails
The physics of how bats fly is surprisingly complicated, in no small part because the legs of many bat species are not well-built for the task. Unlike birds, which have strong enough legs to push off from the ground and take flight, most bats’ legs are too skinny to do this. Instead, they take more of a “dive bomber” approach, dropping down from an elevated point and then flapping and gliding their way along – and that’s where their tail comes in.
For most bats, their tail works in conjunction with their hind legs to help them lift off, stay in the air, or both. The hind legs, the tail’s skeleton, and cartilaginous extension around the ankle region known as the calcar (otherwise known as a keel) are the main components involved in this.
In the case of free-tailed bats, the tail tends to be covered with a cartilage-like substance. In many cases, it can also protract. These tails are often highly flexible and, as demonstrated below, plan an instrumental part in these bats’ ability to fly. In addition, some bats whose tails extend out at least somewhat can use them to feel their way along crevices and otherwise navigate.
Free-tailed bats who use their tails to help them remain airborne often enjoy an aerodynamic speed advantage as well. Taken together, these factors make the tail region one of the most important parts of these bats’ bodies, especially in terms of flight and movement.
It’s also worth noting that while both birds and bats have tails that they use for flying, their construction is quite different. Birds have feathers and hollow bones, the combination of which is what allows them to fly by pushing off and achieving lift. By contrast, as mentioned, bats drop down and then flap and glide their way along, and instead of feathers they have skin and bone stretched out to allow for flight, but the construction is radically different from tails and tail feathers in birds.
So if not takeoff per se, what role does a tail play in allowing bats to fly? The answer to that pertains mostly to the free-tailed variety, and has to do more with how bats achieve one of the primary requirements for any bird, bat, plane, or any flying thing to achieve flight – thrust.
As many a high school physics class has said, to achieve flight you have to generate enough lift to counteract the force of gravity pushing you back toward earth. In birds, bats, and planes, this is achieved primarily with wings and tails. To massively condense the complexity of the process, air rushes beneath the wings and tail to a great enough degree that it generates the requisite lift needed for flight – and to achieve that, you need forward and upward thrust “pushing” you and the air upward. Think of a paper airplane versus the real thing. The latter, once “thrust” into the air by you, merely glides along until it eventually falls to the ground, whereas the former, via propellers or jet engines, are constantly producing lift which helps keep the plane in flight.
Birds and bats likewise flap their wings, forcing air beneath them and creating a bit more thrust and impetus forward for themselves. Both bats and birds can also use their tails as part of this equation, and some bats can actually flap their tails faster than their wings, hence why they are so important for achieving the thrust they need. These tend to be the free-tailed bats, which are particularly strong fliers.
In addition, they can use their tail as a stabilizer of sorts to help control the direction of their flight by reducing drag and making it easier to control the path of their flight. The directionality and speed of tail flaps can also vary depending on the species and whether they prefer to take off in a straight line or use greater loops or comparatively haphazard flight patterns instead. In addition to thrust and stabilization, as with birds and planes’ tails, bat tails can also be used to help with landing.
Finally, unrelated to flight, female bats can sometimes carry newborn bats in their tail membranes.
Bats Without Tails
Of course, that isn’t to say that all bats have tails. On the contrary – there are several species of bats that don’t have them, especially those on the smaller end of the spectrum.
The Bumblebee Bat, for example, is so tiny that it barely weighs as much as a penny. Being so small, it should come as no surprise that it does not have a tail. Likewise, many of the other tiniest Microbats in the world lack a tail. A consequence of this is that these bats are not able to take off from the same positions as their bigger cousins.
That said, most bats have tails, and while some also use them for hunting, carrying their young, or other reasons, most use their tails for the same purpose – to achieve thrust and better stabilize their flight paths. Bats are already conventional fliers, but this is one way in which, even if their tails are constructed differently, they fall in line with how birds and planes achieve and maintain thrust.
For all the attention paid to bats’ wings, the Tail of Their Tails is just as instrumental to their ability to fly.