A Bat’s Inverted Sleep Position

by Anupum Pant

I have written about sloths in the past. In that post, we appreciated the way their bodies are engineered to stay inverted for most of their lives. It turns out, a bat’s body is designed (rather evolved) in a similar way, which enables them to relax and sleep upside down. In this post, I would like to discuss – why did they evolve this way and how do they do it?

If you are interested to know more about bats, you will definitely like this post from the archives. [Bats can See]

How can bats manage to sleep like this?

Humans sleep in a horizontal position, cows sleep with their eyes open, horses sleep in a standing position, and of course, bats sleep in an inverted position. What makes an animal sleep in the position they do, is basically their anatomy – the way their bodies are designed. While sleeping upside down might seem as an anomalous behavior to us, it is a normal position for the bat’s body. Like we don’t exert energy when we are lying down, bats’ bodies don’t consume extra energy for hanging down like that.

Firstly, a bat’s claw is like a hook. A better way to understand why this helps is, to look at a converse behavior – the way a human hand works. We use up energy to contract tens of muscles and make up a hook with our fingers; this is not a normal state of our hand. Also, our relaxed hands are open where we don’t exert any energy and we sleep with our hands in that position. A bat’s claws are designed in a completely inverse fashion; they are hooked in the normal position. They don’t take up energy to make them into hooks, they are like that. And they sleep like that – which enables them to hang without using energy.
So, unlike our hands, a bats’ closed fist is their relaxed position. They have to contract tendons and use energy to open them up. This anomalous talon design allows them to hang in a relaxed position.

Bat's Talons - Normal position

Secondly, unlike every other bird, a bat can’t take off from an upright position, or from the ground. They have to be inverted to start flying. This is because they have relatively weaker wings which can’t make them fly from a stationary position. Think of an X-51A Waverider, which has to be carried on a B-52 plane and dropped down to start a flight. They drop down for a very small amount of time and beat their wings vigorously to start a flight. Since, they have to wake up inverted to go flying and catch a meal, they go to sleep like that.

Why did they evolve this way?

They’ve evolved this way to simply stay away from the predators:

  1. By hiding up in a place where not many predators would look – under a bridge, roof of the cave and dark tree canopies. Also, at places like these, they don’t have to compete with other birds for a place.
  2. And by escaping quickly in case of an attack by attaining instant flight [see above].

Bats Can See

by Anupum Pant

While every teacher around the world is busy teaching their kids that bats are blind, the contrary is actually true. Bats aren’t really blind and they can see pretty darn well even in low light. In fact, their eyes work better than our eyes do in a dimly lit environment (eg. Moon light).

None of the bats’ 1100 species are completely blind. Although, there are a few which depend heavily on a technique called echolocation to navigate around objects which are near, they still have to use eyes to see objects which are far away. Additionally, most bats like to hunt in complete darkness (to avoid competition from other birds), so they use echolocation during such times [because eyes need at least some amount of light to be present]. The daylight hours spent by them to groom or sleep don’t demand much of their visual skills, but that doesn’t make them blind.

One way in which bat’s vision is poorer than our visual ability, is that they can’t see colors like we do. Everything they see is in black and white. This disability, if you may call it one, is compensated by their ability to detect light waves whose frequencies lie beyond the human visible spectrum. Flying foxes, however, which are actually bigger bats, can see colors.

So, simply put, bats can see, but they don’t have to use their eyes to hunt or move around. This makes your teacher wrong when he/she says chides you with the phrase – “Blind as a bat”

Bonus Bat Facts

  1. Bats don’t carry rabies. However, like humans, the disease affects some bats.
  2. Apart from vampire bats found in Mexico, Central America and South America, no other bats suck blood.
  3. Bats hunt insects above your head, they aren’t interested in your hair or your eyes.
  4. Bats can catch insects with their tail or wing membranes.
  5. Fruit bats are also known as flying foxes, they eat fruits.
  6. Bats collectively eat tonnes of insects and protect our crops.
  7. Some bats eat fish and frogs.
  8. Bats’ dung, is rich in nutrients. It is mined from caves, bagged, and used by farmers to fertilize their crops.

Echolocation: A bat echolocates by sending out streams of high-pitched sounds through its mouth or nose. These signals then bounce off nearby objects and send back echoes. By “reading” these echoes with its super-sensitive ears, the bat can determine the location, distance, size, texture and shape of an object in its environment. In some cases, a bat can even use echoes to tell insects that are edible apart from those that aren’t. – [Source]

 

A Few Things About Sloths Everybody Should Know

by Anupum Pant

A few days back, on 20th October, Sloth Day was celebrated all around the world. You’d be thinking, what is so good about these strange animals, that makes people have a special day around them. Well, in that case, you need to read this.

What are these creatures?

Sloths are slow animals that make even cows look extremely active. They are so slow that they are almost stationary and algae grows on their hair. Most of their life is spent on trees hanging upside down. They hang on trees to protect themselves from the predators on the ground. Their bodies are so well engineered to stay inverted that the hair on their bodies, is oriented in the opposite direction – growing from stomach to back (This helps them to stay dry by draining water easily). Even dead sloths have been know to retain their grip and remain suspended after death. They come down only around once a week to excrete. They eat, sleep, travel, find partners, mate, give birth and even raise young ones in the canopies.

Although sloths might seem gross, creepy and unseemly, they really aren’t that bad. Sloths are sweet looking [1] [2] [3] animals (especially their babies, they are adorable) who can also swim efficiently and move wisely. We can definitely learn a lot from them.

Their diet is unbelievable

Sloths eat only leaves throughout their lives. They chew leaves slowly like cows to extract whatever nutrients they can. Sloth intestines are also adapted to extract the maximum out of their poor quality food, they are unusually long. They often like to shift to a different kind of leaf after a day or two. This balances their nutrient intake. Humans couldn’t possibly survive on a leafy salad diet for a very long time.

To save energy, sloths drop the temperature of their bodies at night. Even their bodies have more bones than muscles to prevent wastage of energy through muscular movement. After the Orangutan they are the most energy efficient animals.

Other facts about them

Sloths have blunt teeth to chew leaves properly, have large claws to hang on to branches and inverted fur orientation (as also mentioned before). Another interesting thing about them is that they have remained physically un-evolved for a long time because they don’t really have to compete with anyone else for their diet.

Mutualisms

This is where the awesomeness of Sloths come in. Sloths are home to a several kinds of other organism (tiny ones living in their fur). These organism depend on sloths (hosts) for various things and in turn provide an advantage to their hosts. This is called mutualism.

  1. Algae + Sloth – Algae, for instance, uses the long grooves on sloth hair to grow with a secure footing. As a rent for this safe apartment, the algae gives them [sloths] a nice shade of green color to camouflage on trees. This and their still bodies make them virtually impossible to spot with the naked eye. The camouflage protects them from eagles.
  2. Bacteria + Sloth – Apart from the several other bacteria which live inside a sloth to digest the leafy diet, two kinds of Cyanobacteria live on sloth furs too. These bacteria also give sloths a nice gray hue which helps them in the same ways as above.
  3. The Sloth Moth – The Pyralidae Moth also live on Sloths. These feed on the algae which grows on the fur. In return for the good food, moths give them nothing. Yes, nothing. This is called Commensalism.
  4. Others – Similarly, various other organisms like flies, mites and three types of beetles are often found living in a Sloth. Up to 900 beetles have been found on a single Sloth!

There is so much more to write about these amazing little creatures who provide for so many other creatures too. I’ll keep it for the second part that I’ll write some other day. So the next time you see a Sloth crossing the road, carefully pick it up by holding its mid body and gently place it on a tree. Remember to use a glove/cloth.