Login
Password

Forgot your password?

The Science Behind Bats

By Edited Jun 22, 2016 0 0

They're the only mammals that fly, use echolocation to hunt in darkness with shocking accuracy, hang out, literally, all day in a bat cave and have unique leathery wings.

Bats are unique little (and big) creatures and surprisingly they are full of science.

The smallest of bats is commonly called a bumble-bee but is also known as Kitti's hognose bat and with a wingspan of six inches it is a heavy weight contender in the smallest mammal title match boxing ring. On the other end of the size scale we have the Malayan Flying Fox Bat - I thought the picture was a hoax the first time I seen it. It has a wingspan as wide as six feet. Considering that there is anywhere from 950 species to 1200 species of bats worldwide[1] one is bound to get size extremes.

Bats are actually very cool animals and do all sorts of amazing things for humanity. Honestly they do. They eat bugs - like mosquitoes and spiders -, spread and pollinate seeds, important to medical research among a few. They have wings that are distinct from a feathered bird and not only look different but also function differently – not to mention they look a little like arms. They use echolocation to hunt at night and are incredibly accurate – one bat, the horseshoe bat, can hover and pluck a spider from its web[1]. Even how it hangs around all day on skimpy little underdeveloped hind legs is unique and of interest to science.

Bats are incredibly varied and complex creatures – big or small. Some migrate, some hibernate. Some are vegetarians, some are carnivores and yet others are both, omnivores. Some are cute, a few uglies and a few more are oddball looking.

They are found all over the world with the exception to the polar zones of Arctic and Antarctica and some islands are devoid of bats as well. They are in cities and urban centres, barns, mountains, forests, your attic ... teasing, but maybe if you haven't up there in a few years.

I adore animals that have a status as a relic – like turtles and alligators, but bats have been around for more than fifty million years[2], which is longer than many modern animals. They are fascinating, remarkable and awesome creatures of the night.

Bat Wings

The wings of bats are quite likely their most distinctive and remarkable feature. The meaning of the name of their order, Chiroptera, means hand-wing. In German the word for bats translates to flying mice and they do look like flying mice. Both are accurate descriptions, they look like mice with wings and the wings resemble hands. But if you hold a bat with its wings spread and a light source behind it, it looks eerily human.

Bat Anatomy
A hundred million years ago, give or take a few years, bats evolved from some non flying type of mammal that likely lived in the trees – like a lemur or squirrel today. Actually some modern squirrels and lemurs have developed this little extra piece of skin that gives them a little extra lift and oomph when air-borne in a leap from tree to tree.

This modern-day mutation is thought to have happened to the bats ancestors and evolved from there as those with the mutation survived better. Every couple of generations slightly extending the wing over millions of years, till it is how it looks today[2].

Bat wings are incredibly complex producing thrust, lift and hover to help them to  chase their prey, fly long distances, and nimbly maneuver the skies. 

Bat wings are different than bird wings in many ways other than just not having feathers. For starters they're designed differently. A birds wings comes out from just the chest and back area. On a bat the wings usually runs the full length of the bats body, from shoulder to ankle and in a few cases to the digits on the end of the 'arm'. This wing membrane is an extension of the bat's skin, an external and internal layer with blood vessels and muscles in between and can stretch up to four hundred times its size[1]. If torn it heals quite fast but the membrane is both flexible and tough but not rigid.

Bat Wing Anatomy
Bats have 'thumbs' and wrists. The wrist helps to support specific motions of flying and are responsible for the quick changes a bat makes in air. The thumb, or the piece that looks a little like a claw on the wing end is used for a variety of things; fighting, climbing and food handling.

Bats with large thumbs are likely living or in an area that requires a little more climbing and crawling and as such the claw is longer and stronger, due to constant use. But thumbs come in large and small sizes are not necessarily related to bat size.

Wings appear leathery and bald, but they're actually covered with very tiny hairs and in a few species they have tufts of hair or fringes of hair. The function of the hairs on wings is unknown, unproven and unverified. Some believe it helps with aerodynamics[3] and others see it more sensibly that the fur assists in camouflage or in keeping the bat warm.

Imagery is the best way to see the differences in bat wings from birds, with a human for comparison. In the image, above this paragraph, shows a birds bone structure that is much shorter than a bats bone structure. This short structured bone is more rigid in nature, it allows the bird to flap its wings up and down, providing it with lift and power. The feathers of a bird allow for air to escape from under its wing which allows for greater height.

A bat on the other hand, has longer bones with the leathery membrane wing covering it to the tips, this allows more flexibility and gives the bat more maneuver-ability. A bat's wing is similar to a human hand and fingers in the sense of motions, a bat's wing does more than just up and down motions due to its less rigid structure.

Think about birds in flight – graceful, powerful and soaring. A bat in flight, to our eyes, resembles a bumbling drunken type of flight. They are all over the place flying quite erratically and for people watching them in action for the first time can find themselves surprised at how clumsy they look in the air, compared to bird. Bats fly but rather oddly.

Birds can stand or run to attain flight, their wings provide them with lift and power and can take off from most anywhere. A bats flexible wings allows them a greater maneuverability in the air, but they can't just take off from the ground or fly from a running start, they have to be up on something and drop to attain flight.

Their flexible membrane wings are not rigid enough to provide powerful lifting action of birds, but their clumsy looking flying does in fact produce lift says theoretical biologist Anders Hedenström of Sweden's Lund University

“this seemingly awkward motion in fact produces lift. It actually generates a useful force also on the backswing, which is a very good thing when it hovers,"[5]

The physical motions of a bat flying is incredibly complex, a tiny adjustment while in the air results in diving and swooping with incredible precision to either avoid an obstacle, find pollen and fruit or catch the tiny erratically flying bugs they hunt. Luckily they do not need lift or power as birds do and rely on not only greater maneuver-ability but also a slower speed.

Bat wing Muscles
The muscles in a bats wings are tiny, unique and weak called plagiopatagiales[4]. Science has known about them forever, but have never fully explained how they work in tandem with the rest of the bat or their use in flying (other than creating a flapping). Some believe these tiny muscles are more than just, well muscles, that they act as an activator allowing the bat to know how far stretched his wings are, or perhaps as Jorn Cheney, a graduate student suspect, a variety of activators all working together to allow for morphing or the exerting of force on the wing, essentially giving the bat its ultimate mobility[4].

We may see clumsy and drunk looking flying from most bats at night, we also see that it hides a maneuverability that birds do not have – such as quick or tight turns – as well as processes we still do not fully understand.

But it works for bats and that is all that matters.

How Bat Wings Work

Echolocation - I See You

Echolocation - I See you

Many people believe bats are blind or have bad eye sight, that they use echolocation all the time to see. And this is just not true. Bats can see quite well, not eagle well but more than good enough. They use echolocation as a tool to assist with night hunting of insects, and not as a replacement to sight.

Bats have been here at least fifty million years now they can't be that bad of hunters on their own. Their real hunting weapon is found in their ability to use echolocation and even a specialized form or style of it unique to some species of bats. With echolocation a bat can detect objects as thin as a human hair or as small as a mosquito.

When a bat emits a high-pitched noise – humans can not hear it – it behaves just like our yelling and echoing back. The difference is a bats brain reads the waves to tell it distance, size of object, location and even what direction it is moving in. The bats brain does what our machines and mathematics do and it does it as quickly we process a picture. It can process the tiniest of changes in a wave due to the unique folding found in bat ears and faces. It could be seen as a filter of sorts, or even a blank sheet of paper. The bat makes its noise, the sound wave comes back,hits the bat in the face and a picture is drawn for the bat as to where everything is and not just the one bug.

Bat bio sonar how it works
When the wave returns the brain registers which ear the wave returned to first. If the right ear feels the wave before the left does, then the object it is measuring or targeting is on the right.If the wave returns to the left ear first, then the target is obviously on the left side. When a wave that was sent out hits something, it returns quicker than the portion of the wave that has to travel further to hit something before returning. The differences in return time to the ears may be no more than a fraction of microsecond but the bat registers it instantly - its automatic and requires no conscious thinking.

The vertical position is decided by where the wave hits the ear or face. An example a wave hits the outer folds of the ear from above then the 'bug' is above the bat and vice versa. If a bats wave returns to the left ear before the right ear and strikes the left ear from below, the bat will know the target is to the left and below him.

The size of the object in the bats radar can be determined using the intensity of the echo - a smaller object will reflect a smaller portion of the sound wave and as such will produce a less intense echo. Obviously bigger objects reflect a larger portion of the sound wave back and thus a more intense echo.

Humans experience the Doppler effect when a car blaring a horn approaches then rushes past us. As the car approaches we hear the horn loudly and as it passes us it starts to get less loud. You would think the horn sound would be the same level of loudness whether in approaching or passing so long as it is the same distance from you.

But what actually happens is as the car is moving quickly towards you, it is compressing those sound waves into a tighter set of waves (the pushing of particles), so we hear the horn loudly. As it passes us the waves are more spread out so it sounds less loud [7]

Animals use it too. To figure out which direction the object is moving is based on pitch (loudness). If the echo has a low pitch (less loud) the target or object is moving away and respectively, if it is a higher pitch the object is moving towards them.

The Doppler Effect

The speed of the object is achieved through two echolocation waves and the differences in them show speed. So if a bug is flying at a bat and the first echolocation pins it at, lets say 10 feet away, the second echolocation pins it at now 2 feet from the bat. The bats brain will process the time of the echolocation differences and the differences in distance to determine speed.

All of this is performed and processed in seconds, and its usually a repeating process.

Individually this is how bats use echolocation, but a bat doesn't use one at a time, it process all the information – size, speed, location and direction – all at once in overlapping images and we must not forget that it is still using its other senses such as vision and smell.

When a bat emits a high-pitched noise the sound waves bounce off everything in the area and send back complex images, getting more cluttered every time it sends out a echolocation call ... so how does it know which returned wave belongs to the bug and not the leaf. Since bats are quite accurate in their hunts, they are clearly not guessing.

Using two potted plants – one that had differently designed and built dragonflies of many different materials on it and the other having no dragonflies at all on it, researchers at the University of Ulm in Germany set out to answer this very question.

Every time a bat went into the flight cage, it headed straight to the plants and hovered along and in front of each plant, inspecting the individual parts of a plant. If it detected something on the plant (whether flower head, stem or leaf) the bat would either move towards it or move its face in its direction. Emitting echolocation calls steadily while shifting around - it essentially scanned the section of plant it was interested in. This scan took no more than a few seconds to complete and identify whether it was a target (food).

In the experiment the bats scanned the plants with dragonflies but never the plant without any. It also discriminated between the various dragonflies. Obviously the one complete and accurate dragonfly was snatched up by all the bats. The paper dummies and smooth-winged aluminum dummies were rejected immediately[9]. The others all had varied reactions.

Bat Dinner - Dragonflies
It seems that bats have a built-in catalogue of bug classifications or what they classify as prey – caterpillars, mosquitoes or other insects. In the case of dragonflies the characteristic cross-shape of a dragonfly is key. According to the study all the bats preferred four wings over two, but no wings over two (possibly seen as caterpillars). The study also suggests that bats can differentiate between materials or the reflective properties of them[9]. For example bats in the wild can distinguish between a real twig and a stick bug (which looks a lot like a twig), quite possibly because of the different materials over the two items – bark on one and a chitinous body on the other.

A popular belief for a while was that bats sent out one long continuous echolocation call and sorted targets from non targets based on the picture it received. But long calls would send back a steady, continuous and overlapping set of images, the bats hunting in heavily wooded areas such as rainforest or forest, used a series of short calls of varying intensities or pitches. This short call prevented the overlapping of images and the range of pitches or frequencies provided more minute details.

This type of 'searching' is known as gleaning, the researchers involved believe that the combination of hovering in flight (scanning), short call echolocation and a broader range of frequencies is how bats find and target prey in specific locations or situations[8].

They are essentially forming an acoustic search image or template of prey based on size, prey they have encountered and remember the experience.

More recently (2014) it's been seen that bats also use echolocation to 'jam up' rival bats sonar[10], giving them an advantage over other bats hunting in the area.

There is a lot going on when bats open their little mouths.

Hanging Around in the Bat Cave

Bat caves are not cool – they have poop all over the floor - but what happens in them while the bats hang around and sleep all day is interesting. Not in the Batman cool toys in the garage way, but close. Bats spend the daylight hours hanging upside down in secluded dark spots such as under bridges, roof of a cave, hollowed out trees, people's barns or attics and pretty much anywhere else that lets them hang high and securely. You can even see them out hanging in secluded forests in larger colonies.

There are reasons why they roost this way and not just sitting up on a rafter or branch waiting out the daylight hours. For starters it is just safer for bats to be out of daylight and away from the swifter, more powerful birds of prey that hunt during the day. They tend to roost in large colonies cause we all know that more

Hanging Fruit Bats
numbers are safer than just a few. And add some extra protection by choosing out of the way, not easily seen areas, that many predators won't bother with. They are also the only animals that can roost upside down and as such their roosting spots are often quiet due to the fact that there is so little competition for them.

Bats can not just take off in flight like birds do, their membrane wings do not allow for lift or power and their rather under developed legs don't let them run very fast, in fact bats tend to crawl. They need to be up higher and drop, using a unique back swing wing flap they can take to flight quite easily this way and no, birds can't 'take off' like bats do. By sleeping upside down it puts them in the perfect position to just let go if necessary and take to the skies.

Hanging upside down in the manner that bats do is clearly important to them for a number of reasons. But how do they do it? Why doesn't the blood rush to their heads? How do those tiny feet and scrawny little legs hold them up there for hours and hours? And more importantly, how do they not poop on themselves while hanging up there?

It was once widely believed that bats had either individual valves or a series of valves that prevented the blood from pooling in their upside down heads, or controlled the flow of blood only allowing little bits of blood in at a time as was needed. Bats when they hang upside down are using minimal energy and resting and can not consciously control their blood flow.

Solid hypothesis. But wrong.

Hanging Bat

In all the science research and studies on bats, not one single bat has these valves in them. It was finally figured out that bats blood vessels are tiny, and the bat itself is relatively small and due to these factors it can regulate its own blood flow easily as it doesn't take much work to do[1]. Even in the largest of bats, there are no valves, there is more work to be done to fully understand this feature of bats but it most certainly does not involve valves.

When a human wraps their hand around an object to pick up your arm contracts several different muscles which engages numerous tendons to make the fingers curl and clench and hold, the muscles have to stay engaged to continue holding the object. Your relax your muscles and the object will fall.

In bats we see a physiological adaptation that allows them to hang and not use their muscles the entire time they are upside down. Their talons work in the same manner as our hands, but the tendons used for hanging are not connected to leg or feet muscles but the bats upper body.

The bat flies into the roosting spot finds a spot to roost that as a surface it can grip, once in position it will open its claws around the area it will hang from then simply lets its body relax. Voila a hanging bat.

The bat uses gravity, the upper body pulls down on the tendons from the weight of the bat, that downward gravity pull causes the talons to clench. So long as the bats weight is a downward pull the bat will hang. It does not need its muscles to be contracted at all. In fact if it dies while hanging it stays in that position, it doesn't just 'release' and fall down because gravity is still working and holding it there even when it dies.

This is how those underdeveloped legs of bats manage to hold on and hang for twelve hours or more a day. When it is ready to release and fly it simply has to flex other muscles that retract the talons.

And the poop question ... they are smart, they don't poop upside down, they either hang upside down or they are pooping, they never do the two together. If a bat is sleeping and nature calls, they use their thumbs to flip right side up, do the business and flip back to upside down. Kind of like a midnight run to the bathroom when your still half asleep and blaming your partner for the puddle in the morning.

Myths and fear have blinded many people to the virtues of the bat, but they play important roles for the ecosystem and they help humans in several ways. Bug eaters, pollinators, seed spreader, vampire-bats have unique blood (anti-coagulant) we study for our own medical needs, science is hoping to mimic it's echolocation to assist blind people as well as mimic its wings for drones or robotics and finally we pay cold hard cash for its poop, to fertilize our soils and gardens.

Bats that Hang
Advertisement
Advertisement

Comments

Add a new comment - No HTML
You must be logged in and verified to post a comment. Please log in or sign up to comment.

Bibliography

  1. Alina Bradford "Facts about Bats." LiveScience. 25/09/2014 <Web >
  2. Tom Harris "The Bat." How Stuff Works. 25/09/2014 <Web >
  3. "Bat Wing Anatomy." Animal Diversity. 25/09/2014 <Web >
  4. Rebecca Boyle "Bats use mini muscles to tweak their wings and drones could too.." Popular Science. 25/09/2014 <Web >
  5. "Bat wing strokes unlike a birds." Scientific American. 25/09/2014 <Web >
  6. paul mirocha "Bat FAQ." Paul Mirocha Bat Pics. 25/09/2014 <Web >
  7. "Echolocation." Bat Conservation Trust. 25/09/2014 <Web >
  8. "How do bats echolocate and how are they adapted to this activity? ." Scientific American. 25/09/2014 <Web >
  9. Inga Geipel, Kirsten Jung and Elisabeth K. V. Kalko "Perception of silent and motionless prey on vegetation by echolocation in the gleaning bat." Royal Society Publishing. 28/09/2014 <Web >
  10. Carrie Arnold "Bats Make Calls To Jam Up Other Bat Signals." National Geographic. 7/11/2014 <Web >

Explore InfoBarrel

Auto Business & Money Entertainment Environment Health History Home & Garden InfoBarrel University Lifestyle Sports Technology Travel & Places
© Copyright 2008 - 2016 by Hinzie Media Inc. Terms of Service Privacy Policy XML Sitemap

Follow IB Pets & Animals