Nocturnality

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Owls are well known for being nocturnal, but some owls are active during the day. Owl at Night.jpg
Owls are well known for being nocturnal, but some owls are active during the day.

Nocturnality is a behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.

Contents

Nocturnal creatures generally have highly developed senses of hearing, smell, and specially adapted eyesight. [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 humans (except for night owls), 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.

Origins

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

While it is difficult to say which came first, nocturnality or diurnality, a hypothesis in evolutionary biology, the nocturnal bottleneck theory, postulates that in the Mesozoic, many ancestors of modern-day mammals evolved nocturnal characteristics in order to avoid contact with the numerous diurnal predators. [3] 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 is not needed anymore due to the evolution of compensatory sensory systems, such as a heightened sense of smell and more astute auditory systems. [4] 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. [4] The anomaly to this theory were anthropoids, who appeared to have the most divergence from nocturnality of all organisms examined. While most mammals did not 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]

Advantages

Resource competition

The honey badger, a nocturnal animal. Honey Badger (Mellivora capensis) (17425848662).jpg
The honey badger, a nocturnal animal.

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. [5] This means they are not in competition for each other's prey. Another niche that being nocturnal lessens competition within is pollination - nocturnal pollinators such as moths, beetles, thrips, and bats have a lower risk of being seen by predators, and the plants evolved temporal scent production and ambient heat to attract nocturnal pollination. [6] Like with predators hunting the same prey, some plants such as apples can be pollinated both during the day and at night. [7]

Predation

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

Nocturnality is a form of crypsis, an adaptation to avoid or enhance predation. Although lions are cathemeral, and may be active at any time of day or night, they prefer to hunt at night because 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. [8] 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. [9] One of the reasons that (cathemeral) lions prefer to hunt at night is to conserve water. Hamiltons Frog, found on Stephens and Maud islands, stays hidden for the majority of the day when temperatures are warmer and are mainly active at night. They will only come out during the day if there are humid and cool conditions.

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. [10]

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 on a ski slope in Finland gives the area a hazy, brightened sky. Light Pollution (5346483205).jpg
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. [11] 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 is detrimental to their nocturnal prey trying to avoid them. [8]

Orientation

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. [12] 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. [8] 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. [8] [12] 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. [12]

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. [12] On a day-to-day basis, species can see significant changes in their internal temperatures, their general movement, feeding and body mass. [13] These small scale changes can eventually lead to a population decline, as well as hurting local trophic levels and interconnecting species. [13] Some typically diurnal species have even become crepuscular or nocturnal as a result of light pollution and general human disturbance. [13]

Reproduction

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. [8] 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. [14] This hurts the overall fitness of the species, which is concerning considering the overall decrease in amphibian populations. [14]

Predation

Some nocturnal predator-prey relationships are interrupted by artificial lighting. Bats 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. [8] 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. [8] 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. [13]

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. [15] Carnivorous predators however are less timid of the disturbance, feeding on human waste and keeping a relatively similar spatial habitat as they did before. [15] 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. [15]

In captivity

Zoos

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.

Pets

Hedgehogs are mostly nocturnal. European hedgehog (Erinaceus europaeus).jpg
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. [16]

See also

Related Research Articles

<span class="mw-page-title-main">Night monkey</span> Genus of New World monkeys

Night monkeys, also known as owl monkeys or douroucoulis, are nocturnal New World monkeys of the genus Aotus, the only member of the family Aotidae. The genus comprises eleven species which are found across Panama and much of South America in primary and secondary forests, tropical rainforests and cloud forests up to 2,400 metres (7,900 ft). Night monkeys have large eyes which improve their vision at night, while their ears are mostly hidden, giving them their name Aotus, meaning "earless".

<span class="mw-page-title-main">True owl</span> Family of birds

The true owls or typical owls are one of the two generally accepted families of owls, the other being the barn owls (Tytonidae). This large family comprises 230 living or recently extinct species in 24 genera. The typical owls have a cosmopolitan distribution and are found on every continent except Antarctica.

<span class="mw-page-title-main">Moth</span> Group of mostly-nocturnal insects in the order Lepidoptera

Moths are a group of insects that includes all members of the order Lepidoptera that are not butterflies. They were previously classified as suborder Heterocera, but the group is paraphyletic with respect to butterflies and neither subordinate taxon is used in modern classifications. Moths make up the vast majority of the order. There are approximately 160,000 species of moth, many of which have yet to be described. Most species of moth are nocturnal, although there are also crepuscular and diurnal species.

<span class="mw-page-title-main">European nightjar</span> Migratory bird found in Eurasia and Africa

The European nightjar, common goatsucker, Eurasian nightjar or just nightjar, is a crepuscular and nocturnal bird in the nightjar family that breeds across most of Europe and the Palearctic to Mongolia and Northwestern China. The Latin generic name refers to the old myth that the nocturnal nightjar suckled from goats, causing them to cease to give milk. The six subspecies differ clinally, the birds becoming smaller and paler towards the east of the range. All populations are migratory, wintering in sub-Saharan Africa. Their densely patterned grey and brown plumage makes individuals difficult to see in the daytime when they rest on the ground or perch motionless along a branch, although the male shows white patches in the wings and tail as he flies at night.

<span class="mw-page-title-main">Blue-tailed day gecko</span> Species of lizard

The blue-tailed day gecko is a diurnal species of gecko, a lizard in the family Gekkonidae. The species is endemic to the island Mauritius. It typically inhabits warm and humid places and dwells on different trees and bushes.

<span class="mw-page-title-main">Crepuscular animal</span> Animal behavior primarily characterized by activity during the twilight

In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal, vespertine/vespertinal, or both. This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylight and of darkness, respectively. Some crepuscular animals may also be active by moonlight or during an overcast day. Matutinal animals are active only before sunrise, and vespertine only after sunset.

<span class="mw-page-title-main">Anti-predator adaptation</span> Defensive feature of prey for selective advantage

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.

<span class="mw-page-title-main">Zoophily</span> Pollination by animals

Zoophily, or zoogamy, is a form of pollination whereby pollen is transferred by animals, usually by invertebrates but in some cases vertebrates, particularly birds and bats, but also by other animals. Zoophilous species frequently have evolved mechanisms to make themselves more appealing to the particular type of pollinator, e.g. brightly colored or scented flowers, nectar, and appealing shapes and patterns. These plant-animal relationships are often mutually beneficial because of the food source provided in exchange for pollination.

<span class="mw-page-title-main">Cathemerality</span> Irregular organismal activity pattern

Cathemerality, sometimes called "metaturnality", is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are undertaken. This activity differs from the generally monophasic pattern of nocturnal and diurnal species as it is polyphasic and is approximately evenly distributed throughout the 24-hour cycle.

<span class="mw-page-title-main">Crypsis</span> Aspect of animal behaviour and morphology

In ecology, crypsis is the ability of an animal or a plant 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 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 or plants.

<span class="mw-page-title-main">Diurnality</span> Behavior characterized by activity during the day and sleeping during the night

Diurnality is a form of plant and 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 except for a zeitgeber. 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.

<span class="mw-page-title-main">Greater noctule bat</span> Species of bat

The greater noctule bat is a rare carnivorous bat found in Europe, West Asia, and North Africa. It is the largest and least studied bat in Europe with a wingspan of up to 46 centimetres (18 in) and is one of the few bat species to feed on passerine birds. Greater noctule bats are the only bat species to hunt birds on the wing rather than when roosting. The greater noctule bat has wings adapted for open-air hunting and uses echolocation frequencies above the hearing range of birds.

<span class="mw-page-title-main">Pueo</span> Subspecies of bird

The pueo is a subspecies of the short-eared owl and is endemic to Hawaii. The pueo is one of the more famous of the various physical forms assumed by ʻaumākua in Hawaiian culture.

<span class="mw-page-title-main">Golden masked owl</span> Species of owl

The golden masked owl is a barn owl endemic to the island of New Britain, Papua New Guinea. It is also known as New Britain barn owl, New Britain masked owl, Bismarck owl and Bismarck masked owl.

<span class="mw-page-title-main">Matutinal</span> Natural world activity in early morning

Matutinal, matinal, and matutine are terms used in the life sciences to indicate something of, relating to, or occurring in the early morning. The term may describe the morning activities of crepuscular animals that are significantly active during the predawn or early hours and which are then active again in the evening’s twilight. During the morning twilight period and shortly thereafter, these animals partake in important tasks, such as scanning for mates, mating, and foraging.

<span class="mw-page-title-main">Sleep in animals</span>

Sleep in animals refers to a behavioral and physiological state characterized by altered consciousness, reduced responsiveness to external stimuli, and homeostatic regulation observed in various animals. Sleep has been observed in mammals, birds, reptiles, amphibians, and some fish, and, in some form, in insects and even in simpler animals such as nematodes. The internal circadian clock promotes sleep at night for diurnal organisms and in the day for nocturnal organisms. Sleep patterns vary widely among species. It appears to be a requirement for all mammals and most other animals.

<span class="mw-page-title-main">Ecological light pollution</span>

Ecological light pollution is the effect of artificial light on individual organisms and on the structure of ecosystems as a whole.

Pollutant-induced abnormal behaviour refers to the abnormal behaviour induced by pollutants. Chemicals released into the natural environment by humans impact the behaviour of a wide variety of animals. The main culprits are endocrine-disrupting chemicals (EDCs), which mimic, block, or interfere with animal hormones. A new research field, integrative behavioural ecotoxicology, is emerging. However, chemical pollutants are not the only anthropogenic offenders. Noise and light pollution also induce abnormal behaviour.

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