Nocturnal animals have a mirror-like membrane at the back of their eyes behind the retina that basically reflects light back through the eye. This layered membrane is called the tapetum.

Many nocturnal animals, though not nocturnal birds, have a good sense of smell and often communicate with scent marking. That sense of smell comes from the Jacobson’s organ located in the roofs ...

It is the rods that become highly specialized in nocturnal animals. In fact, many bats, nocturnal snakes and lizards have no cones at all, while other nocturnal animals have just a few.

Nocturnal animals have evolved to survive in darkness. Hoffman’s two-toed sloths seldom need to come to the ground, instead feeding silently in trees, camouflaged by algae that grows in their fur.