Bright side of the night – 2.1.3

Adaptation to nocturnal life

Senses of smell, touch, sound, vision

The senses of animals have evolved and been refined to work best either during the day, or during the night. Animals that are mostly active during darkness use the visual system less than diurnal animals—those active during the day—do. On the other hand, nocturnal animals provide over heightened acoustic senses, like owls or bats, and olfactory senses (“sense of smell”), like moths and most mammals. In general, it is key to recall that every animal has its own sensory bubble. While we perceive our environment as we do, other creatures smell, hear, feel, and see their environment completely different.

Ears and echolocation

The owl’s most important sensory organ is the ears, which helps it to locate and strike prey in total darkness. Bats use echolocation to orientate themselves in the dark and to catch insects. Echolocation relies on emitting ultrasounds and reading the echo.

Highly sensitive eyes

The eyes of some nocturnal animals are very sensitive to light. Grass frogs, but also the medium vine hawkmoth, a moth, can even see colours in the dark. Night insects are in principle able to see colours at night as well as to navigate by means of celestial bodies.

Meanwhile, the common toad needs only a fraction of the light produced by the starry sky to catch its prey at night (0.00001 lux or lx, the unit of illuminance). To put this into perspective: the maximum brightness of the full moon is 0.3 lx.

Glowing Eyes

Many mammals tend to be nocturnal, especially smaller species. Mammals originally specialised in nocturnal life, and only some diurnal groups, such as primates, evolved colour vision. Nocturnal animals usually exhibit distinct camouflage colours that allow them to hide from predators during the daytime resting period. Nocturnal mammals often have large pupils to take in more light, large lenses to minimize spherical aberrations and many rods (light-dark perception) in the retina, the light-sensitive layers of nerve tissue at the back of the eye. Then again, they have few cone sensory cells in the eye, limiting their colour vision. This makes e.g. diurnal squirrels and birds almost blind at night. Owls in turn, but also some mammals like the fox, deer, and wild cat, have a retro-reflective layer behind the retina. This layer leads to enhanced light sensitivity, and it is also the reason for the glow in many animals’ eyes when they are illuminated.

Light your fire: The magic of bioluminescence

Bioluminescence is the ability of living organisms to produce light by themselves or with the help of symbionts. The purpose is to ward off enemies or to attract prey and mating partners. Fireflies are probably the best-known creatures in our latitudes that glow at night. The light in their bodies is the result of a chemical reaction in which a bioluminescent substrate (Luciferin) is oxidized by an enzyme (Luciferase). In some areas, the night also exposes bioluminescent mushrooms.

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*Barn Owl. Image by cocoparisienne ̶ Pixabay*

*Deer under the night sky. Image by 5187396 ̶ Pixabay*

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