VIDEO: How Nocturnal Animals See in the Dark
September 20, 2016 | Erica Tennenhouse
Photo credit: Izass/Wikimedia (CC BY-SA 3.0)
Through the eyes of tarsiers, cats, toads, and hawk moths.
Walking through a forest, without a flashlight, on a moonless night probably sounds like a bad idea. That's because humans have exceedingly poor vision under low light conditions. But many animals have impressive abilities to see in the dark, thanks to a variety of eye adaptations that help compensate for the lack of light.
In this TED-Ed video, biologist Anna Stöckl, from Lund University in Sweden, explains how vision in nocturnal animals has evolved to deal with the dark.
Eyes use the photoreceptors in their retinas to detect light particles, or photons. The photoreceptors translate the information from these photons into electrical impulses that can be understood by the brain. The brighter the light, the more photons hit the eyes. But in the dark, photons become scarce and less reliable.
Massive eyes have allowed tarsiers to master the nocturnal life. In fact, a tarsier's eyeballs are each as big as its brain. With a wider pupil and larger lens, the eyes are able to collect more photons.
Cats rely on a special reflective membrane beneath their retina, which collects light and re-emits it, giving the retina a second chance to absorb the photons. The membrane is called a tapetum lucidum, and it's what makes cats' eyes appear to glow in the dark.
For toads, night vision is all about slowing down. Their photoreceptors are 25 times slower that those of humans, allowing them to collect more photons at each time interval. Although this improves their vision, it also slows their reaction time because they only get an updated image of the world every four seconds.
Some insects, including the hawk moth, have the impressive ability to see flowers in color, even on moonless nights. Their brains group together information from neighboring photoreceptors, which reduces the sharpness of images, but also allows them to capture more photons than individual receptors would.
With such a wide array of night vision adaptations among animals, it's no wonder that forests are teeming with activity, even in the dead of night.
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