Through The Eyes Of Our Wild
Many guests visiting South Africa’s beautiful reserves and wondrous wildlife experience a sunset or night drive during their stay with many wondering what they will see at night. A question our guides often get asked while on safari is ‘how can a predator see at night?’
As humans, we have near perfect eyesight during the day but, come nightfall, without the use of a torch or some form of light, it is much more difficult to make anything out. However, the optical anatomy of our nocturnal mammals is very different.
As you drive around during the day on safari, across the grassland Savannah, you’ll see plenty of general game. Zebras with their famous black and white stripes, impalas with their white underbelly and two toned brown upper body, and Kudus with their white stripes and spots. To us, mammals such as these seem like walking targets at night however, they do have some tricks to employ when there are predators on the prowl.
Most mammals see in black and white while some see a few shades of yellow and blue. Species regarded as prey use something called “disruptive colourisation.” This allows them, along with their spots, stripes and different shades of colour, to break their shape when they are stationary which is especially important at night when predators are on the hunt.
Another form of camouflage is “concealing colouration.” This is when mammals, especially small mammals like duikers are very well hidden and blended in with the surrounding due to their colouration. Lions are also an example of this as their habitat which is the Savannah grassland, matches their tawny colourisation.
Many young animals when born are very different in colour compared to their parents like the Hyena for example. When born, Hyena pups are Jet black, why? Hyena pups are sometimes left with sub adults at the den site, their black colour allows them to hide in the shadows undetected should the den come under attack from other predators.
Humans have near perfect binocular vision, meaning both eyes can focus on an object so our eyes face forward. Species that feed on the open Savannah during the day, will spend most of the time feeding on the grass with their heads down. To be able to see if anything is sneaking up on them, their eyes are placed at the side which allows them to have peripheral vision. This means they can see things to the side of them so binocular vision would be of no use.
Every animal has the type of vision that is required for them to have high-definition vision like us. This requires a lot of energy which is needed to supply their very complex nerve cells. In general, nocturnal animals typically have larger eyes than humans. The pupils as with humans, will dilate to let in more light whereas, the eyes of nocturnal species open wider in low light in order to let more light in. The light is then passed through the pupils and focused by the lens and finally, the retina that is connected to the optic nerve.
Retinas have more sensory nerve cells than anywhere else in the body which makes them very complex. Inside the retina, there’s light receptor cells, rods and cones. The cones for bright light and the rods for low light.
The main reason for predators having the ability to see better during the night, albeit in black and white, is a structure not found in us humans called the Tapetum. The tapetum basically maximizes the amount of light that reaches the retina. Generally, when guests are on a sunset or night drive, they’ll be asked to be on the look out for eyes in the dark reflected back as the spotter on the vehicle uses a powerful spotlight. This is due to the mirror like membrane that reflects the light which has already passed through the retina a second time and allows the light another chance to strike the light-sensitive rods.
The use of a flashlight is also a great way to identify predators as big cats and dogs as their eyes reflect a green light. Also, if you’re using your camera to photograph these unique animals at night time, you might want to switch the light and flash off otherwise you will have two bright alien-looking eyes in your picture. So, in a nutshell, it’s the tapetum that allows nocturnal wildlife to see during the twilight hours.
Some examples of the best vision in the animal kingdom:
The American Bald Eagle: This species has the best vision amongst the eagle kingdom and can see 7-8 times better than humans.
The Cheetah: This epic big cat can spot prey of up to 5kms away while on the run while humans can potentially see up to 3 kms away.
The Bluebottle Butterfly is the critter with the worlds best colour vision as far as we know. Where we have three different types of cones to detect colour, they have a whopping fifteen, some of which see in the UV spectrum.
The Red Dragonfly with it’s large prominent faceted eyes possess a large field of vision. Due to the organization of the dragonfly eye, these insects can see significantly more colours than humans, very similar to the Bluebottle Butterfly.
The creature with the most sophisticated eye structure is the Mantis Shrimp. They are the only creature to see Circular polarised light.
Chameleons have some of the strangest eyes on the planet, which can move independently of each other. This results in almost 360-degree vision. The reptile can also switch between monocular vision, which is when both eyes are used separately and, binocular vision, when both eyes are used to look at the same scene.
As you see, eyes with various marvelous features have evolved in all kinds of animals. The exciting thing is, not all animals need highly colourful or detailed vision. all animals have a vision that suits their particular needs, helping them find food and protect themselves in a complex world with multiple signals and dangers. Human eyes also have features that were needed by our ancestors to survive.