You are sitting with friends at the table and have some nice talks. You see there is no water left and you are thirsty. What are you going to do? Obviously you stand up and go to the freezer to get some fresh, sparking water. On the way to the freezer you overlook the wall in front of you since you are busy with reading great posts on Steemit. Banging your head against the wall you hear your friends laughing and calling you blind like a bat.
Every now and then you hear some horrific stories about blood sucking vampire bats that want your precious fluid of life. A widespread believe is that bats are blind and only navigate by echolocation. You seem to lack both: sight and echolocation.
Back to the bats – is it true that the only flying mammals are blind or is this just another widespread misunderstanding?
How do bats navigate?
In the following we will use the two main categories of bat, Megachiroptera and Microchrioptera, and describe their most efficient way of navigating and surviving in nature. The word chiroptera comes from the Greek and means "hand-wing". This name was giving due to the structure of bat wings which look similar to the human hand.
Fig1. Bat skeleton. Source
First of all, all bat species can see. None of them is blind, NONE. The myth arose from the fact that most bats are nocturnal mammals that hunt at night. Furthermore bats are born blind but gain their eyesight after few days. Megachiroptera, or simply called Megabats, have well developed eyes they use to collect their nutrients from fruits or nectar and therefore need a proper eyesight.
Microchiroptera, or Microbats, have very poor developed eyes and feed on insects. Some other larger species of Microbats hunt animals such as fish, birds, lizards etc.
While Megabats have proper eyesight Microbats rely on echolocation for navigation. There is only one Megabat species, the Egyptian fruit bat Rousettus egyptiacus, which is able to use a kind to echolocation.
Echolocating animals such as Microbats emit self-produced high pitched squeaks ( ultra sonic) to their environment and detect variations in the reflected sound waves. The echo that bounces off nearby objects or insects is used of navigation and hunting. They compare the sound they emitted with the sound waves they receive and their brain processes these information. The darker it is the more the bats use Echolocation for navigation. Comparing Mega- and Microbats one can see that Microbats have larger ears while Megabats have larger eyes.
Fig.2 Illustration on Animal Echolocation Source
Speaking of bats being blind? Some bats have even far better developed eyes than us humans. Some fruit bats are able to see ultraviolet light! This makes sense since some flowers reflect ultraviolet light.
We humans can’t see UV light because it isn’t in the range of the light spectrum we can see. If you want to know more about the spectrum of light I recommend you to read my Life Explorers - The Human Senses Part I: Sight.
In the late 1930s Donald Griffin made several experiments on bats to study their navigational methods. In the physical laboratories of Harvard they were able to determine that bats use self produced ultra sonic waves that humans cannot hear. He blindfolded the bats and kept their ears shut. The result was that the bats were not able to avoid obstacles set on a course. Opening their eyes they were able to see the obstacles and avoid them. In the next phase the blindfolded them again but left their ears free. Now the bats were able to avoid the obstacles even blindfolded.
In 1944 he identified this phenomena as echolocation.
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Thanks for reading this episode of Myth or Fact! If you enjoyed it feel free to resteem and leave a comment! I would love to know what you think about bats!
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Tim