The visual acuity of tortoises is the best of all reptilian species, which enables them to navigate the world better, find nutritious foods, and avoid deadly predators and dangerous situations.
Tortoises can see up to 17 feet away, have good night vision, and notice various colors. They can see bright colors, like red, better than dark colors, like blue.
Due to the position of their eyes, tortoises’ peripheral vision is excellent while still being able to see what’s in front of them. They’re good at detecting movement but struggle to focus on detail.
Tortoises have two regular eyelids, one upper and one lower, and a third eyelid.
The third eyelid of tortoises (called the nictitating membrane) protects and lubricates the eyes. It can also assist with debris removal and controlling the amount of light entering the eyes.
Tortoises are vulnerable to various eye conditions, including conjunctivitis (red eye), abscesses, injuries, vitamin A deficiencies (hypovitaminosis A), and cataracts.
Tortoises aren’t fast-moving animals, but this isn’t connected to their eyesight. Their color detection and night vision allow them to live long lives and thrive in the wild.
What Is A Tortoise’s Eyesight Like?
Tortoises have amazing eyesight, and they can see better than humans in many ways.
They have an advantage over other animals due to their eye placement. Looking at a tortoise, you’ll notice its eyes are further apart, almost to the side of the head.
Animals with eyes to the sides of their heads are classified as foraging animals.
They need a wide view of the world to increase their chances of finding food. Look at a picture taken with a wide-angle lens, and you’ll better understand how tortoises see the world around them.
If you compare tortoises’ eyes to other foragers, you’ll notice that they aren’t as far apart. Having slightly centered eyes gives tortoises the ability to focus on objects and accurately measure distances.
They may not have full monocular vision and a wide horizontal field, but they have good depth perception, which is superior to most other forager animals.
How Far Can Tortoises See?
According to the Journal of Applied Animal Welfare Science, tortoises can see 17 feet away, although it’s possible they can see even farther.
It’s theorized that tortoise species that live in open areas, like Sulcata tortoises, can see farther than those living in places with lots of foliage, like yellow-footed tortoises.
Tortoises aren’t predatory animals, so they must be able to see danger from afar, giving them time to react. They’re slow-moving, solitary animals that can’t rely on a creep (a group of tortoises) for protection.
Also, seeing so far into the distance is beneficial when looking for food in vast expanses of land.
Can Tortoises See in the Dark?
Tortoises can see in the dark and have surprisingly good night vision, even though they’re diurnal animals. Usually, animals active during the day and sleep at night have poor night vision.
There are various theories about why tortoises have special night vision abilities, including the following:
Tortoises move slowly. When out foraging, they may venture far away from their burrows. Whether or not they find food, they’ll sometimes have to find their way home in the dark.
Hiding from Predators
Tortoises are prey animals. Although they can deliver a painful bite with their beaks, this isn’t as effective against dangerous animals like snakes and coyotes.
When these predators hunt at night, tortoises must be able to hide and avoid detection. A tortoise’s night vision is beneficial in these situations, and tortoises can find a place to conceal themselves.
Lack of Sunlight
Some tortoise species live in areas where there’s lots of foliage. As minimal sunlight comes through, tortoises have evolved to have good night vision.
Can Tortoises See Color?
Tortoises can see various colors. According to the University of Vienna, tortoises can distinguish between colors when visual cues are presented.
It’s a skill they need to find the right food to eat. As stated, tortoises are foragers who spend most of their time looking for sustenance in the wild.
Seeing color allows tortoises to identify foods they enjoy, avoid toxic plants or rotten fruits, and find food based on their nutritional needs.
Without this ability, they’d have to rely solely on their sense of smell. Sniffing every plant or fruit to check if it’s good to eat isn’t ideal, especially for slow-moving tortoises.
Tortoises can speed up the process considerably due to their exceptional color vision.
What Colors Can Tortoises See?
Tortoises can see various colors, including ultraviolet, which is invisible to the human eye. They even have favorite colors, preferring bright colors, like red and yellow, over dark colors, like blue and green.
Tortoises interact more with brightly-colored materials. Researchers suggest that tortoises prefer them due to the colors of the fruits and plants they forage in the wild.
Many have some red or yellow shade, so tortoises instinctively head toward those colors.
Can Tortoises See Red Light?
Of the bright colors a tortoise can see, red is a favorite.
When presented with something yellow, tortoises were more likely to approach if it was food. When presented with something red, tortoises interacted with it extensively, regardless of whether it was food.
If a tortoise ever loses its appetite, offer it safe red vegetables (like red bell peppers) or fruits (if it’s a fruit-eating species of tortoise) to encourage it to eat.
However, surrounding a tortoise with red light, which is unnatural in the wild, may confuse and disrupt its sleeping cycle or appetite.
Tortoise Vision vs. Human Vision
Tortoise vision is better than human vision in certain ways. For example, tortoises have better night vision than humans because they have more rods in their eyes.
Photoreceptors (the cells located in the retinas) contain rods and cones. Cones are responsible for color reception, but rods are sensitive to light.
The more rods an animal has in its eyes, the better it can sense light, even in complete darkness. Tortoises can see ultraviolet light because they have more color receptors than humans.
Because tortoises’ eyes are far apart, they have superior peripheral vision to humans. Although humans can forage like tortoises, we’re much better suited to working with binocular eyes like predatory animals.
This gives humans a better depth of field, so when it comes to measuring distances, we surpass tortoises.