Tuesday, January 17, 2017

#ElephantTuesdays: the elephant´s vision ๐Ÿ˜

The elephant´s eyes are quite small If one compares them with their body dimensions. Their sense of vision is moderate, as they lean more on their olfactory and auditory senses instead.

The eyes of an elephant are located on the sides of the head and therefore provide better peripheral vision, rather than binocular vision. 



Elephants (and especially African Forest elephants) have long eyelashes to protect them from the blowing sand, dirt, debris and the dense vegetation:

original video: ACP0002hmp

In addition to the upper and lower eyelids, and like many other animals, all elephants species have a third eyelid (the so-called nictitating membrane, from latin nictare, to blink) which moves horizontally across the eye, and which works for moisten and protection when bathing or dusting.

Some elephants develop a white ring that encircles the iris as they mature. This ring is similar to an age-ring that may develop in humans (as they age) called arcus lipoides, and does not affect vision.

Elephants are dichromatic; they have two kinds of color-sensors in their retina, one type of cones for *reds and another for greens. That means that they are "color-blind" when you compare them to humans (we are trichromatic: we have three kinds of cones: red, green and blue).

What is also interesting is that they are one of the animals that exhibit arrhythmic vision, that is, their vision changes within the daytime. At night, their eyes are most sensitive to violet light so they can see pretty well under the smallest amount of daylight when the prevailing color of the atmosphere is in the violet range. They have pretty sensitive rods as well (the higher density of rods in the retina, the more sensitive to light one can be), so elephants do a good job when it comes to night vision compared to humans.

The eyesight of the elephants is thought to reach a range of about 46 m. However, this can vary and be much shorter, probably because elephants use their vision sense less than their olfactory and auditory senses. When they focus on their vision, however, they show to react to the smallest ear movement of another elephant placed up to 50 m. in the distance. 


The elephant eyes are amazingly beautiful, and like humans, they can show different colors; the four most common eye colors are dark brown, light brown, honey and gray, but there are more tones like: blue-gray, gold, brown tones, green and yellow, and even the right and left eye of one elephant can be differently colored.




As a curiosity: There have been documented occurrences of elephant herds being led by a blind member, fulfilling amazingly its role as the herd leader.


*Some authors claim that elephants possess cones for reds and blues (deuteranopia) instead of reds and greens : Von Elefanten und Menschen, Fred Kurt (2014).





References:

Murray E. Fowler, Susan K. Mikota (2006): Biology, Medicine, and Surgery of Elephants

Fred Kurt (2014): Von Elefanten und Menschen.

Seaworld Parks & Entertainment: https://seaworld.org/en/Animal-Info/Animal-InfoBooks/Elephants/Senses

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