Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.

Nocturnal creatures generally have highly developed senses of hearing, smell, and specially adapted eyesight. Such traits can help animals such as the Helicoverpa zea moths avoid predators.[1] Some animals, such as cats and ferrets, have eyes that can adapt to both low-level and bright day levels of illumination (see metaturnal). Others, such as bushbabies and (some) bats, can function only at night. Many nocturnal creatures including tarsiers and some owls have large eyes in comparison with their body size to compensate for the lower light levels at night. More specifically, they have been found to have a larger cornea relative to their eye size than diurnal creatures to increase their visual sensitivity: in the low-light conditions.[2] Nocturnality helps wasps, such as Apoica flavissima, avoid hunting in intense sunlight.

Diurnal animals, including squirrels and songbirds, are active during the daytime. Crepuscular species, such as rabbits, skunks, tigers, and hyenas, are often erroneously referred to as nocturnal. Cathemeral species, such as fossas and lions, are active both in the day and at night.

Northern Spotted Owl.USFWS
Owls are well known for being nocturnal, but some owls are active during the day.


Kiwi bird in Christchurch, New Zealand, 2002-01-01
The Kiwi is a family of nocturnal birds endemic to New Zealand.

While it is difficult to say which came first, nocturnality or diurnality, there is a leading hypothesis out in the evolutionary biology community. Known as the "bottleneck theory", it postulates that millions of years ago in the Mesozoic era, many ancestors of modern-day mammals evolved nocturnal characteristics in order to avoid contact with the numerous diurnal predators. A recent study attempts to answer the question as to why so many modern day mammals retain these nocturnal characteristics even though they are not active at night. The leading answer is that the high visual acuity that comes with diurnal characteristics isn't needed anymore due to the evolution of compensatory sensory systems, such as a heightened sense of smell and more astute auditory systems.[3] In a recent study, recently extinct elephant birds and modern day nocturnal kiwi bird skulls were examined to recreate their likely brain and skull formation. They indicated that olfactory bulbs were much larger in comparison to their optic lobes, indicating they both have a common ancestor who evolved to function as a nocturnal species, decreasing their eyesight in favor of a better sense of smell.[3] The anomaly to this theory were anthropoids, who appeared to have the most divergence from nocturnality than all organisms examined. While most mammals didn't exhibit the morphological characteristics expected of a nocturnal creature, reptiles and birds fit in perfectly. A larger cornea and pupil correlated well with whether these two classes of organisms were nocturnal or not.[2]


Resource competition

Being active at night is a form of niche differentiation, where a species' niche is partitioned not by the amount of resources but by the amount of time (i.e. temporal division of the ecological niche). Hawks and owls can hunt the same field or meadow for the same rodents without conflict because hawks are diurnal and owls are nocturnal. This means they are not in competition for each other's prey.


Bat flying at night
Echolocating bats adjust their vocalizations to catch insects against a changing environmental background.

Nocturnality is a form of crypsis, an adaptation to avoid or enhance predation. One of the reasons that (cathemeral) lions prefer to hunt at night is that many of their prey species (zebra, antelope, impala, wildebeest, etc.) have poor night vision. Many species of small rodents, such as the Large Japanese Field Mouse, are active at night because most of the dozen or so birds of prey that hunt them are diurnal. There are many diurnal species that exhibit some nocturnal behaviors. For example, many seabirds and sea turtles only gather at breeding sites or colonies at night to reduce the risk of predation to themselves and/or their offspring.Nocturnal species take advantage of the night time to prey on species that are used to avoiding diurnal predators. Some nocturnal fish species will use the moonlight to prey on zooplankton species that come to the surface at night.[4] Some species have developed unique adaptations that allow them to hunt in the dark. Bats are famous for using echolocation to hunt down their prey, using sonar sounds to capture them in the dark.

Water conservation

Another reason for nocturnality is avoiding the heat of the day. This is especially true in arid biomes like deserts, where nocturnal behavior prevents creatures from losing precious water during the hot, dry daytime. This is an adaptation that enhances osmoregulation.[5] One of the reasons that (cathemeral) lions prefer to hunt at night is to conserve water.

Many plant species native to arid biomes have adapted so that their flowers only open at night when the sun's intense heat cannot wither and destroy their moist, delicate blossoms. These flowers are pollinated by bats, another creature of the night.

Climate-change and the change in global temperatures has led to an increasing amount of diurnal species to push their activity patterns closer towards crepuscular or fully nocturnal behavior. This adaptive measure allows species to avoid the heat of the day, without having to leave that particular habitat.[6]

Human disturbances

The exponential increase in human expansion and technological advances in the last few centuries has had a major effect on nocturnal animals, as well as diurnal species. The causes of these can be traced to distinct, sometimes overlapping areas: light pollution and spatial disturbance.

Light pollution

Light Pollution (5346483205)
Light pollution on a ski slope in Finland gives the area a hazy, brightened sky.

Light pollution is a major issue for nocturnal species, and the impact continues to increase as electricity reaches parts of the world that previously had no access.[7] Species in the tropics are generally more affected by this due to the change in their relatively constant light patterns, but temperate species relying on day-night triggers for behavioral patterns are also affected as well. Many diurnal species see the benefit of a "longer day", allowing for a longer hunting period, which in turn negatively their nocturnal prey trying to avoid them.[4]


Light pollution can disorient species that are used to darkness, as their adaptive eyes are not as used to the artificial lighting. Insects are the most obvious example, who are attracted by the lighting and are usually killed by either the heat or electrical current.[8] Some species of frogs are blinded by the quick changes in light, while nocturnal migratory birds may be disoriented, causing them to lose direction, tire out, or be captured by predators.[4] Sea turtles are particularly affected by this, adding to a number of threats to the different endangered species. Adults are likely to stay away from artificially lit beaches that they might prefer to lay eggs on, as there is less cover against predators.[4][8] Additionally, baby sea turtles that hatch from eggs on artificially lit beaches often get lost, heading towards the light sources as opposed to the ocean.[8]

Rhythmic behaviors

Rhythmic behaviors are affected by light pollution both seasonally and daily patterns. Migrating birds or mammals might have issues with the timing of their movement for example.[8] On a day-to-day basis, species can see significant changes in their internal temperatures, their general movement, feeding, and body mass.[9] These small scale changes can eventually lead to a population decline, as well as hurting local trophic levels and interconnecting species.[9] Some typically diurnal species have even become crepuscular or nocturnal as a result of light pollution and general human disturbance.[9]


There have been documented effects of light pollution on reproductive cycles and factors in different species. It can affect mate choice, migration to breeding grounds, and nest site selection.[4] In male green frogs, artificial light causes a decrease in mate calls, and continued to move around instead of waiting for a potential mate to arrive.[10] This hurts the overall fitness of the species, which is concerning considering the overall decrease in amphibian populations.[10]


Some nocturnal predator-prey relationships are interrupted by artificial lighting. Bats that that are fast-moving are often at an advantage with insects being drawn to light; they are fast enough to escape any predators also attracted to the light, leaving slow-moving bats at a disadvantage.[4] Another example is harbor seals eating juvenile salmon that moved down a river lit by nearby artificial lighting. Once the lights were turned off, predation levels decreased.[4] Many diurnal prey species forced into being nocturnal are susceptible to nocturnal predators, and those species with poor nocturnal eyesight often bear the brunt of the cost.[9]

Spatial disturbance

The increasing amount of habitat destruction worldwide as a result of human expansion has given both advantages and disadvantages to different nocturnal animals. As a result of peak human activity in the daytime, more species are likely to be active at night in order to avoid the new disturbance in their habitat.[11] Carnivorous predators however are less timid of the disturbance, feeding on human waste and keeping a relatively similar spatial habitat as they did before.[11] In comparison, herbivorous prey tend to stay in areas where human disturbance is low, limiting both resources and their spatial habitat. This leads to an imbalance in favor of predators, who increase in population and come out more often at night.[11]

In captivity


In zoos, nocturnal animals are usually kept in special night-illumination enclosures to invert their normal sleep-wake cycle and to keep them active during the hours when visitors will be there to see them.


European hedgehog (Erinaceus europaeus)
Hedgehogs are mostly nocturnal.

Hedgehogs and sugar gliders are just two of the many nocturnal species kept as (exotic) pets. Cats have adapted to domestication so that each individual, whether stray alley cat or pampered housecat, can change their activity level at will, becoming nocturnal or diurnal in response to their environment or the routine of their owners. Cats normally demonstrate crepuscular behavior, bordering nocturnal, being most active in hunting and exploration at dusk and dawn.[12]

See also


  1. ^ Agee, H. R.; Orona, E. (1988). "Studies of the neural basis of evasive flight behavior in response to acoustic stimulation in Heliothis zea (Lepidoptera: Noctuidae): organization of the tympanic nerves". Annals of the Entomological Society of America. 81 (6): 977–985. doi:10.1093/aesa/81.6.977.
  2. ^ a b Hall, M. I.; Kamilar, J. M.; Kirk, E. C. (2012). "Eye shape and the nocturnal bottleneck of mammals". Proceedings of the Royal Society B: Biological Sciences. 279 (1749): 4962–4968. doi:10.1098/rspb.2012.2258. PMC 3497252. PMID 23097513.
  3. ^ a b Torres, Christopher R.; Clarke, Julia A. (2018-11-07). "Nocturnal giants: evolution of the sensory ecology in elephant birds and other palaeognaths inferred from digital brain reconstructions". Proc. R. Soc. B. 285 (1890): 20181540. doi:10.1098/rspb.2018.1540. ISSN 0962-8452. PMC 6235046. PMID 30381378.
  4. ^ a b c d e f g Longcore, Travis; Rich, Catherine (May 2004). "Ecological light pollution". Frontiers in Ecology and the Environment. 2 (4): 191–198. doi:10.1890/1540-9295(2004)002[0191:elp];2. ISSN 1540-9295.
  5. ^ N. A. Campbell (1996) Biology (4th edition) Benjamin Cummings New York. ISBN 0-8053-1957-3
  6. ^ Levy, Ofir; Dayan, Tamar; Porter, Warren P.; Kronfeld-Schor, Noga (2018-11-12). "Time and ecological resilience: can diurnal animals compensate for climate change by shifting to nocturnal activity?". Ecological Monographs. 89: e01334. doi:10.1002/ecm.1334. ISSN 0012-9615.
  7. ^ Gaston, Kevin J.; Davies, Thomas W.; Bennie, Jonathan; Hopkins, John (2012-11-02). "REVIEW: Reducing the ecological consequences of night-time light pollution: options and developments". Journal of Applied Ecology. 49 (6): 1256–1266. doi:10.1111/j.1365-2664.2012.02212.x. ISSN 0021-8901. PMC 3546378. PMID 23335816.
  8. ^ a b c d Witherington, B.E. (1997). "The problem of photopollution for sea turtles and other nocturnal animals". In Clemmons, J.R.; Buchholz, R. (eds.). Behavioral Approaches to Conservation in the Wild. Cambridge: Cambridge University Press. pp. 303–328.
  9. ^ a b c d Gaynor, Kaitlyn M.; Hojnowski, Cheryl E.; Carter, Neil H.; Brashares, Justin S. (2018-06-15). "The influence of human disturbance on wildlife nocturnality". Science. 360 (6394): 1232–1235. doi:10.1126/science.aar7121. ISSN 0036-8075. PMID 29903973.
  10. ^ a b Baker, B.J.; Richardson, J.M.L. (October 2006). "The effect of artificial light on male breeding-season behaviour in green frogs, Rana clamitans melanota". Canadian Journal of Zoology. 84 (10): 1528–1532. doi:10.1139/z06-142. ISSN 0008-4301.
  11. ^ a b c Wu, Yonghua; Wang, Haifeng; Wang, Haitao; Feng, Jiang (2018-01-29). "Arms race of temporal partitioning between carnivorous and herbivorous mammals". Scientific Reports. 8 (1). doi:10.1038/s41598-018-20098-6. ISSN 2045-2322. PMID 29379083.
  12. ^ Debra Horwitz; Gary Landsberg. "Nocturnal Activity in Cats". VCA Antech. Retrieved 7 October 2012.

Aepyornis is a genus of aepyornithid, one of three genera of ratite birds endemic to Madagascar until their extinction about 1000 A.D. The species A. maximus weighed up to 540 kilograms (1,200 lb), and until recently was regarded as the largest known bird of all time. However, in 2018 the largest aepyornithid specimens, weighing up to 730 kilograms (1,600 lb), were moved to the related genus Vorombe.


The Anthropocene is a proposed epoch dating from the commencement of significant human impact on the Earth's geology and ecosystems, including, but not limited to, anthropogenic climate change.As of August 2016, neither the International Commission on Stratigraphy nor the International Union of Geological Sciences (IUGS) has yet officially approved the term as a recognized subdivision of geological time, although the Anthropocene Working Group (AWG) of the Subcommission on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), voted to proceed towards a formal golden spike (GSSP) proposal to define the Anthropocene epoch in the Geologic Time Scale and presented the recommendation to the International Geological Congress on 29 August 2016.Various start dates for the Anthropocene have been proposed, ranging from the beginning of the Agricultural Revolution 12,000–15,000 years ago, to as recent as the Trinity test in 1945. As of February 2018, the ratification process continues and thus a date remains to be decided definitively, but the latter date has been more favoured than others.

The most recent period of the Anthropocene has been referred to by several authors as the Great Acceleration during which the socioeconomic and earth system trends are increasing dramatically, especially after the Second World War. For instance, the Geological Society termed the year 1945 as The Great Acceleration.

Anti-predator adaptation

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

The first line of defence consists in avoiding detection, through mechanisms such as camouflage, masquerade, apostatic selection, living underground, or nocturnality.

Alternatively, prey animals may ward off attack, whether by advertising the presence of strong defences in aposematism, by mimicking animals which do possess such defences, by startling the attacker, by signalling to the predator that pursuit is not worthwhile, by distraction, by using defensive structures such as spines, and by living in a group. Members of groups are at reduced risk of predation, despite the increased conspicuousness of a group, through improved vigilance, predator confusion, and the likelihood that the predator will attack some other individual.

Some prey species are capable of fighting back against predators, whether with chemicals, through communal defence, or by ejecting noxious materials. Many animals can escape by fleeing rapidly, outrunning or outmanoeuvring their attacker.

Finally, some species are able to escape even when caught by sacrificing certain body parts: crabs can shed a claw, while lizards can shed their tails, often distracting predators long enough to permit the prey to escape.


Biretia is an extinct genus of Old World monkey belonging to the extinct family Parapithecidae. Fossils are found from Late Eocene strata in Egypt.

The first discovery of Biretia was a single tooth dated to approximately 37 mya, which was found in 1988 at the Bir el Ater site in Algeria. This species was named Biretia piveteaui. In 2005, two new species were classified, B. fayumensis and B. megalopsis. Both were discovered at Birket Qarun Locality 2 (BQ-2), which is located about 60 mi south of Cairo in Egypt's Fayum depression.

A very small anthropoid, it only weighed around 280 to possibly 380 grams. Fragments from the jaw suggest that it had had very large eyes in proportion to its body size, which would suggest that it was nocturnal. Biretia is unique among early anthropoids in exhibiting evidence for nocturnality, but derived dental features shared with younger parapithecids draw this genus, and possibly 45-million-year-old Algeripithecus (Strepsirrhini), into a morphologically and behaviorally diverse parapithecoid clade of great antiquity."The smallest of the species, B. fayumensis, had an estimated weight of 273 g, while the largest, B. megalopsis, had a weight of about 376g. Adaptations of the skull of B. megalopsis are easily comparable to the modern tarsiers, a small, modern Asian primate with a nocturnal insectivorous lifestyle. We can infer the possibility of a nocturnal lifestyle for B. megalopsis' from the animal's molar roots, which are truncated to accommodate for large eye sockets typical of a nocturnal primate. The large eye structure and similarity to the modern tarsiers also suggests that it has lost its tapetum lucidum. Thus, B. megalopsis demonstrates itself as being the oldest known nocturnal primate.

The genus is otherwise known only from a handful of fossil fragments, including a few maxilla fragments and some teeth and teeth fragments from the different species.

The fossil fragments found for B. fayumensis, new species, include a composite of isolated P2 (DPC 21759C), P3 (DPC 21249E), P4 (DPC 21371A), M1 (DPC 21250D), and M2 (DPC 21539E). For B. megalopsis, new species, maxilla with M1 through M3 (DPC 21358F).


Cathemerality, sometimes called metaturnality, is the behaviour in which an organism has sporadic and irregular intervals of activity during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are performed. It has been defined as follows: "The activity of an organism may be regarded as cathemeral when it is distributed approximately evenly throughout the 24 h of the daily cycle, or when significant amounts of activity, particularly feeding and/or traveling, occur within both the light and dark portions of that cycle."Many animals do not fit the traditional definitions of being strictly nocturnal, diurnal, or crepuscular, often by factors that include the availability of food, predation pressure, and variable ambient temperature. As a result, many species, particularly among primates, may be classified as cathemeral.Alternative patterns of cathemeral activity have been observed in specific lemurs. Seasonal cathemerality has been described for the mongoose lemur (Eulemur mongoz) as activity that shifts from being predominantly diurnal to being predominantly nocturnal over a yearly cycle. The Common brown lemurs (E. fulvus fulvus) have been observed as seasonally shifting from diurnal activity to cathemerality.


Cistecephalidae is an extinct family of dicynodont therapsids from the Late Permian of South Africa, India and Zambia. It includes the genera Cistecephalus, Cistecephaloides, and Kawingasaurus. Cistecephalids are thought to have had a fossorial or burrowing lifestyle, with adaptations such as broad skulls, strong forelimbs, and squat bodies. A similar group of dicynodonts called the pylaecephalids were also fossorial, although to a lesser extent than cistecephalids. Cistecephalids showed a high level of endemism, with each of the five known species unique to a single region.

Crepuscular animal

Crepuscular animals are those that are active primarily during twilight (that is, the periods of dawn and dusk). This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylight or the hours of darkness, respectively. The term is not precise, however, as some crepuscular animals may also be active on a moonlit night or during an overcast day. The term matutinal is used for animals that are active only before sunrise, and vespertine for those active only after sunset.

The time of day an animal is active depends on a number of factors. Predators need to link their activities to times of day at which their prey is available, and prey try to avoid the times when their principal predators are at large. The temperature at midday may be too high or at night too low. Some creatures may adjust their activities depending on local competition. Therefore, for many varied reasons, crepuscular activity may best meet an animal's requirements by compromise.


In ecology, crypsis is the ability of an animal to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and mimicry. Crypsis can involve visual, olfactory (with pheromones), or auditory concealment. When it is visual, the term cryptic coloration, effectively a synonym for animal camouflage, is sometimes used, but many different methods of camouflage are employed by animals.


Diurnality is a form of plant or animal behavior characterized by activity during daytime, with a period of sleeping or other inactivity at night. The common adjective used for daytime activity is "diurnal". The timing of activity by an animal depends on a variety of environmental factors such as the temperature, the ability to gather food by sight, the risk of predation, and the time of year. Diurnality is a cycle of activity within a 24-hour period; cyclic activities called circadian rhythms are endogenous cycles not dependent on external cues or environmental factors. Animals active during twilight are crepuscular, those active during the night are nocturnal, and animals active at sporadic times during both night and day are cathemeral.

Plants that open their flowers during the daytime are described as diurnal, while those that bloom during nighttime are nocturnal. The timing of flower opening is often related to the time at which preferred pollinators are foraging. For example, sunflowers open during the day to attract bees, whereas the night-blooming cereus opens at night to attract large sphinx moths.


Euparkeria (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close to the ancestry of Archosauria, the group that includes dinosaurs, pterosaurs, and modern birds and crocodilians.

Euparkeria had hind limbs that were slightly longer than its forelimbs, which has been taken as evidence that it may have been able to rear up on its hind legs as a facultative biped. Although Euparkeria is close to the ancestry of fully bipedal archosaurs such as early dinosaurs, it probably developed bipedalism independently. Euparkeria was not as well adapted to bipedal locomotion as dinosaurs and its normal movement was probably more analogous to a crocodilian high walk.

Ghost crab

Ghost crabs are semiterrestrial crabs of the subfamily Ocypodinae. They are common shore crabs in tropical and subtropical regions throughout the world, inhabiting deep burrows in the intertidal zone. They are generalist scavengers and predators of small animals. The name "ghost crab" derives from their nocturnality and their generally pale coloration. They are also sometimes called sand crabs, though the name refers to various other crabs that do not belong to the subfamily.

Characteristics of the subfamily include one claw being larger than the other, thick and elongated eyestalks, and a box-like body. The differences in claw sizes, however, are not as marked as in male fiddler crabs. The subfamily includes 22 species in two genera.


Morganucodonta ("Glamorgan teeth") is an extinct order of basal mammaliaformes, the precursors to crown-group mammals (Mammalia). Their remains have been found in southern Africa, Western Europe, North America, India and China. The morganucodontans were probably insectivorous and nocturnal. Nocturnality is believed to have evolved in the earliest mammals in the Triassic (called the nocturnal bottleneck) as a specialisation that allowed them to exploit a safer, night-time niche, while most larger predators were likely to have been active during the day (though some dinosaurs, for example, were nocturnal as well).


Mullerornis is a genus of extinct elephant birds (Aepyornithidae) of Madagascar.


Nemegtosaurus (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. Nemegtosaurus was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found. The skull resembles diplodocoids in being long and low, with pencil-shaped teeth. However, recent work has shown that Nemegtosaurus is in fact a titanosaur, closely related to animals such as Saltasaurus, Alamosaurus and Rapetosaurus.

Night monkey

The night monkeys, also known as the owl monkeys or douroucoulis, are the members of the genus Aotus of New World monkeys (monotypic in family Aotidae). The only nocturnal monkeys, they are native to Panama and much of tropical South America. Night monkeys constitute one of the few monkey species that are affected by the often deadly human malaria protozoan Plasmodium falciparum, making them useful as non-human primate experimental subjects in malaria research.

Night owl (person)

A night owl, evening person or simply owl, is a person who tends to stay up until late at night, or the early hours of the morning. Night owls who are involuntarily unable to fall asleep for several hours after a normal time may have delayed sleep phase syndrome.

The opposite of a night owl is an early bird – a lark as opposed to an owl – which is someone who tends to begin sleeping at a time that is considered early and also wakes early. Researchers traditionally use the terms morningness and eveningness for the two chronotypes or diurnality and nocturnality in animal behavior. In several countries, especially in Scandinavia, early birds are called A-people and night owls are called B-people.

Nocturnal (disambiguation)

Nocturnality describes sleeping during the daytime and being active at night.

Nocturnal may also refer to:

Night owl (person), a person who tends to stay up until late at night


Scaphognathus was a pterosaur that lived around Germany during the Late Jurassic. It had a wingspan of 0.9 m (3 ft).


Urotrichini is a tribe of the mole family, and consists of Japanese and American shrew-moles. They belong to the Old World moles and relatives branch of the mole family (Talpidae). There are only two species, each of which represents its own genus. The name "shrew-moles" refers to their morphological resemblance to shrews, while generally being thought of as "true moles". The species are the Japanese shrew mole, True's shrew mole and American shrew mole.In Japan, the word "Himizu" (ヒミズ) may refer to both to the Japanese shrew mole in particular and Urotrichini in general; when True's shrew mole is distinguished from the general Himizu forms, the feminine diminutive word "Hime" is added to refer to the smaller size of that species. Although they are common in Japan, their alpine habitats, small size, and secretive lifestyle makes them generally unknown except among some mountain people and researchers.

Internal rhythms
External cycles
See also
Food webs
Example webs
Ecology: Modelling ecosystems: Other components
Patterns of evolution

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