In Depth Study: Bats’ Eyesight
You’ll have heard of the saying “blind as a bat” and it’s usually used in quite a disrespectful manner.
But how true is it? Are bats really blind? Or do they have a degree of vision? Surely Nature wouldn’t intend for a creature that flies to be unable to see at all?
Mammals Which Are Blind At Birth
In fact although bats are born without sight (as are many mammals), after seven to nine days they can see. Puppies and kittens are blind at birth, but then their eyes open.
Bats are nocturnal creatures and their food is insects. To catch these, they have perfected a darting motion which looks aimless, but in fact is perfectly developed to capture quickly moving prey. Perhaps it is this motion that gave rise to the saying “blind as a bat” and also the fact they are active in the dark.
Using Sonar Waves To ‘See’
Other nocturnal hunters, owls and cats, possess perfectly adapted eyesight for hunting in dark and dim conditions. Bats are not equipped in this way. Instead they have a highly developed sonar system which allows them to guide their flight and avoid hitting objects in the dark.
A bat’s sonar works when the bat emits a high pitched squeak, inaudible to humans, which travels as a sound wave and hits buildings, trees and other objects, bouncing back. This informs the bat where obstacles are and allows them to navigate safely. The special word for this ability is echolocation. So in fact bats use their sense of sound to fly accurately, rather than their sense of sight.
Which Bats Can See In Colour?
There are about 1,100 different species of bat, all of which can see. Bats are divided into two main groups. The first includes the bats known as Flying Foxes which have big eyes and use both sight and smell to catch their food. Flying foxes can discern colours and have good vision during the daytime which they rely on. If a night is dark with no moon a Flying Fox is unable to fly.
The other group of bats are smaller and eat insects. These use the aforementioned echolocation to discover food. The bats are aware of different light levels and so know at dusk that it is time to go hunting. However, these bats can also see to an extent during the daytime when they do use their visual capabilities.
Charlotte blogs about eyesight for Directsight, leading prescription glasses online retailers.
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