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What do the Terms Crepuscular, Diurnal, and Nocturnal Mean?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

Crepuscular, diurnal, and nocturnal are terms which are used to describe the period of the day during which an animal is active. Many animals develop distinctive behavioral patterns which are part of their overall adaptation to the environments that they live in. Periods of activity tend to be easy for biologists to observe, and they are commonly used as tools to assess whether or not animals are stressed, frustrated, or pressured into unusual behavior. Knowledge about when an animal is supposed to be active can also be used as an indicator to suggest that an animal might be sick; owls, for example, are usually seen at night, making an owl a cause for concern if it is seen at noon.

When an animal is said to be crepuscular, it is active during the twilight hours at dawn and dusk. The word "crepuscular" is derived from a Latin word which means "twilight." Many animals take advantage of the twilight to feed, seek out water, and engage in other behaviors because they know that predators are not as active in the twilight. Visibility is also challenging at dawn and dusk, making it easier for animals to hide from potential threats. Rabbits and cats are both famously crepuscular.

Rabbits are crepuscular, meaning active at dusk and dawn.
Rabbits are crepuscular, meaning active at dusk and dawn.

Nocturnal animals, on the other hand, only come out at night. Many of these animals have a specially developed sense of vision which helps them to see in the dark, and they often have excellent hearing as well. There are a number of reasons for an animal to be nocturnal; many desert animals, for example, are active at night because it is cooler, and their rate of water loss is decreased as a result. Two famous nocturnal animals are bats and owls.

Owls are a well-known nocturnal creature.
Owls are a well-known nocturnal creature.

Animals who are active during the day are known as diurnal. Like crepuscular and nocturnal animals, the daily patterns of diurnal animals are established through circadian rhythms, patterns built into their body chemistry. Being active during the day certainly has some advantages, especially for animals with poor visibility like humans. Humans also have a tendency to encourage diurnal behavior among the animals they interact with; dogs, for example, are naturally crepuscular, but they learn to become diurnal through human interactions.

Deer are crepuscular, meaning daylight and nighttime can be particularly worrisome.
Deer are crepuscular, meaning daylight and nighttime can be particularly worrisome.

A disruption of an animal's established biological rhythms can be harmful. Nocturnal animals, for example, tend to feel very disoriented when they are forced to be active during the day, and this can cause a feeling of stress and unhappiness which can have a negative impact on the animal's health. Diurnal animals are not adapted to being active at night, which means that they can be vulnerable to predation when they are out and about after dark, while crepuscular animals like deer can feel very stressed when they are out in the heat of the day or late at night, and this can cause them to engage in odd behaviors like running into traffic.

Frequently Asked Questions

What does it mean when an animal is described as diurnal?

Bats are a well known nocturnal animal.
Bats are a well known nocturnal animal.

Diurnal animals are active during the daylight hours and rest at night. This pattern aligns with the human daily routine. Diurnal creatures, such as squirrels and humans, have adapted to life in the light, which often means better color vision and long-distance visibility. According to studies, about 20% of mammal species are diurnal, with the rest being nocturnal or crepuscular.

How do nocturnal animals differ from diurnal ones?

Bats sleep during the day and awake at night.
Bats sleep during the day and awake at night.

Nocturnal animals are active during the night and rest during the day. They have evolved to thrive in the dark, with adaptations like enhanced night vision, acute hearing, and sensitive whiskers or antennae for navigation. Owls, for instance, have remarkable night vision, allowing them to hunt efficiently in low-light conditions. Nocturnal behavior helps these animals avoid daytime predators and competition for resources.

What are crepuscular animals, and why aren't they considered nocturnal or diurnal?

The Sunda slow loris is a type of nocturnal animal.
The Sunda slow loris is a type of nocturnal animal.

Crepuscular animals are those that are most active during twilight, which includes dawn and dusk. This behavior is neither strictly nocturnal nor diurnal but is adapted to the low-light conditions of twilight to avoid predators and extreme temperatures. Examples include rabbits and deer. Crepuscular species benefit from the reduced competition for food and the ability to hide in the shadows during these times.

Can an animal be both diurnal and nocturnal?

While most animals are specifically diurnal, nocturnal, or crepuscular, some species exhibit flexibility known as cathemeral behavior, where they can be active at any time of day or night. This adaptability allows them to respond to various environmental pressures, such as predation or human activity. Lemurs in Madagascar are a prime example of cathemeral animals, adjusting their activity patterns to food availability and temperature.

How do the activity patterns of crepuscular animals benefit them?

Crepuscular animals gain several advantages from their twilight activity. The low light levels during dawn and dusk make it harder for predators to spot them, while still providing enough visibility for these animals to forage or hunt. Additionally, crepuscular timing allows them to avoid the midday heat and the competition for food and resources that is more intense during full daylight or complete darkness.

Are there any environmental factors that can change an animal's activity pattern?

Yes, environmental factors such as climate, habitat disruption, availability of prey, and human activity can influence an animal's activity pattern. For instance, extreme temperatures can push diurnal animals to become more crepuscular to avoid the heat. Similarly, nocturnal animals in urban areas may shift their activity to avoid human disturbance. These changes demonstrate the adaptability and resilience of wildlife in response to their changing environments.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

anon946188

What does crepuscular mean -- that they hunt in the day and night?

anon357743

An animal that shows diurnal and nocturnal behavior is classified as cathemeral.

anon345206

I think the statement about humans not being nocturnal because of poor visibility should be amended. I have no doubt that you are referring to the fact that we have poor night vision, but some people may mistake that you are stating that humans have poor vision overall, which is certainly not the case, since we have excellent color vision and detail bias.

We use our vision so much because it is our sharpest sense and we rely on it so much that being caught in the dark in which our type of vision serves us poorly puts us at a major disadvantage. We can't use the sense we get most of our perception from.

anon106969

Being nocturnal usually means you are a predator, out hunting. Being crepuscular, however, often means you are vulnerable, finding the times when most other predators will be sleeping or awakening. Being diurnal often means you are prey, but it is the most variable of the three. Many animals are known to be diurnal, and are very predatory.

anon79502

Possible advantages of being nocturnal are that (A) you're more of a prey species, and the predatory species in your community are diurnal; or, (B) you're a predator, and your prey are easiest to catch at night.

anon46901

how do nocturnal and diurnal compare with one another?

anon46592

Being nocturnal allows you to operate in the absence of the heat of the sun. Also, most animals require a large amount of light to guide themselves safely through their environments, so nocturnal hunters gain an advantage over sleeping prey.

anon45347

Which one's best?

anon38852

simultaneously diurnal, nocturnal and crepuscular animals are classified as "tired".

anon33941

What is an animal called that is both diurnal and nocturnal...perhaps crepuscular as well?

anon10469

why is being nocturnal an advantage to an animal?

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    • Rabbits are crepuscular, meaning active at dusk and dawn.
      By: rusugrig
      Rabbits are crepuscular, meaning active at dusk and dawn.
    • Owls are a well-known nocturnal creature.
      By: hitman1234
      Owls are a well-known nocturnal creature.
    • Deer are crepuscular, meaning daylight and nighttime can be particularly worrisome.
      By: awhelin
      Deer are crepuscular, meaning daylight and nighttime can be particularly worrisome.
    • Bats are a well known nocturnal animal.
      By: cheri131
      Bats are a well known nocturnal animal.
    • Bats sleep during the day and awake at night.
      By: andrewburgess
      Bats sleep during the day and awake at night.
    • The Sunda slow loris is a type of nocturnal animal.
      The Sunda slow loris is a type of nocturnal animal.