Whether you’re a carnivore skulking through the undergrowth in the dead of night or a prey animal trying to survive until sunrise, in the unforgiving wild, night vision is a matter of life or death
Cats
Cats can see with one-sixth of the light humans need
There are two types of light-sensitive cells in the eyes. Cones are responsible for colour vision and require a lot of illumination to work, while rods can’t pick out colour but function in extremely dim conditions. Human eyes contain around 120 million rods, but cats have up to eight times as many. This creates super-charged night vision abilities that allow cats to sense their surroundings with a fraction of the light required by the human eye.
Rods are also responsible for peripheral vision due to their positioning around the outer edge of the retina. Additionally, low-light rod cells are the eye’s most sensitive motion sensors and notice miniscule movements in the dark. Cats use their expanded field of vision and finely tuned motion detection to snare prey that a human wouldn’t even notice.
Dolphins
Dolphins shine beams of sound
Darkness doesn’t stop a dolphin from finding food. These marine mammals sleep sporadically through the day rather than snooze at night, so they need to be able to navigate the pitch-black water.
In the absence of light dolphins emit a series of click sounds into the ocean in front of them. Just like light bounces off an object and into the eye, the sound waves rebound off any objects in the water and back to the dolphin.
The returning clicks aren’t received by the ear. Dolphins lost their external ear flaps over millions of years and only a tiny pinhole remains on each side of the head. Instead, rebounding sound travels along the lower jaw, which is in contact with the inner ear.
Tarsier
Tarsiers have eyes bigger than their brain
Despite measuring only 12 centimetres (4.7 inches) long, a tarsier’s eyes are the same size as those of an orangutan. This is an adaptation to a nocturnal lifestyle of leaping from tree to tree in search of insect prey. The tarsier’s long-range vision helps it detect insects, small birds or even snakes through the dense Asian jungle. The rear of the eyes have pronounced indentations called foveae, in which rods and cones are packed very densely. This pit is a mechanism for producing a stable eyeline like a high-powered telescope.
Tarsiers are thought to be fairly primitive primates and may use similar survival tactics as some of the very first mammals that lived just after the demise of the dinosaurs. These animals came out at night to avoid predators, and their surviving descendants continue to do the same. Tarsier fossils from 50 million years ago have been discovered to be almost identical to their modern-day counterparts.
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