Why do some animals see clearly only at night

Since the innermost part of the eyeball of higher animals and birds is the retina, it is the site of light stimulation. The retina receives light, which is then transmitted through the nervous system to the cerebrum. In the retinas of these animals there are needle-shaped cells that receive low light.

In general, birds that are blind during the day, like chickens, have more needle-shaped cells in their retinas, and fewer rod cells. So they can’t see well at night. Birds and animals can see clearly at night, in the retina of the eye contains many rod cells. In autumn, a number of small birds fly from Siberia, using the weak light of the stars, to navigate across the sea to Japan. This means that birds that fly at night more or less have needle cells so they can continue to fly at night.

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In the eyes of the civet, the needle cells are slightly more numerous than the rod cells, so the cuckoo can be active on moonlit nights.

The eyes of some animals light up at night because there is a special reflective layer at the back of the eyeball (called the tapetum lucidum) that increases the amount of light absorbed by the photoreceptors in their eyes.

This is an optical phenomenon, the layer of tapetum lucidum acts as a light amplifier. Normally, the retina captures part of the light entering the eye, but lets another part pass through. The tapetum lucidum mirror layer will reflect this passage back to the retina, giving the photoreceptors in the eye a second chance to absorb light.

This helps animals see better, especially at night, because the photoreceptors receive more light, so the resulting image of the subject is also brighter.

Although tapetum lucidum is naturally colored, its color depends on the minerals that make up the reflective tapetum lucidum crystals and the angle of view of the eye. The most common colors we see include white with blues, greens commonly seen in tigers, dogs or antelopes.

Many animals, especially nocturnal species, have glowing eyes so they can see better, easily hunt for food, and avoid danger from lurking predators.


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