Photo: The possum is a nocturnal (night-time) animal
A nocturnal animal is active at night and sleeps during the day. However, some animals that appear to be nocturnal may also be active during the day.
Animals, such as possums and owls, are strictly nocturnal. They only come out in total darkness. Kangaroos are classified as nocturnal, but they are also crepuscular, being most active during dawn and dusk.
Elephants and the red fox are predominately active during dawn and dusk, but they are also active at night. Echidnas, on the other hand, vary the times they are active according to their environment. For example, if the climate is hot, the echidna will forage for food at night. But in cooler weather, it will come out during the day. While the echidna's behaviour is dictated by its desire to stay cool, it is just the opposite with some snakes, such as the red-bellied black snake. Being cold-blooded and needing to keep warm, these snakes will hunt at night if the weather is hot. But if the weather is cold, they will only do so during the day.
So, the term nocturnal is used quite broadly to describe a group of animals that are usually active when it is dark.
Time of the Day Animals are Active? Day, Evening, Night or Undecided
There is often confusion as to whether an animal is nocturnal or not. This is because some of these animals may seem to be active during other times of the day.
Animals have been categorised into three broad groups based on the time of day that they are most active.
Photo: Times of day chart
Diurnal (Daylight) animals are usually active during daylight and rest when it gets dark.
Crepuscular (Twilight) animals are active during dawn and dusk (twilight) and rest at other times of the day.
Nocturnal (Night) animals are active during the night when it's totally dark and rest during other times of the day. Most mammals (69%) are nocturnal.
Many animals, however, don't fit conveniently into these categories as they may be seen to be active across these time zones and may adjust their behaviour to several factors – typically the climate.
It is common practice to classify many animals that come out when it gets dark as nocturnal, even though they may actually be crepuscular animals. One reason might be the tongue-twisting name – crepuscular – which few can remember or pronounce.
Why are Some Animals Nocturnal? Why Does Australia have so many Nocturnal Animals?
Its Cooler at Night
Most nocturnal animals live in arid environments such as deserts. Take Australia, for example. It is the driest inhabited continent on earth. Most of the land is dry, and the climate is hot. As a result, many Australian animals, especially the marsupials, have adopted a nocturnal lifestyle to avoid the blistering daytime heat. This behaviour of coming out at night when the temperature is cooler conserves precious water lost.
Its Easier to Avoid Detection at Night
Many animals use the cover of darkness to evade predators. However, it should be noted that many predators are nocturnal too, and use the darkness to hide themselves and ambush their prey.
Competition
Some animals have adopted night-time behaviour to minimise competition for food. For example, the hawk and owl hunt in similar environments and for similar prey, but one hunts during the day and the other hunts at night. In this way, they minimise competition between each other.
Special Adaptations for Nocturnal Life Characteristics of Nocturnal Animals
Nocturnal animals have evolved special adaptations that help them survive in the dark.
Eyes (Sight)
Animals such as possums and cats have excellent low-light eyesight.
Ears (Sound)
Photo: The bilby has big ears and nose
The kangaroo, bilby, and rabbit have an acute sense of hearing. This allows them to detect danger at great distances in the dark. Many bats use echolocation which acts like a radar. The bat emits a high-frequency sound that bounces off objects, and the animal's ears pick up the bounced signals to help it navigate through the dark.
Nose (Smell)
Some animals have an acute sense of smell. Koalas with their large noses and elephants with their sensitive trunks, for example, can sniff out the most appropriate leaves to eat in the dark.
Australian Nocturnal Animals Why are Most Australian Animals Nocturnal?
Most Australian animals are nocturnal and crepuscular. That is, they are only active when its dark. Australia is arid with very little water, and the climate is hot. As a result, many Australian animals, especially the marsupials, have adopted a nocturnal lifestyle to avoid the blistering daytime heat. This behaviour of coming out only at night when the temperature is cooler conserves precious water lost.
