In zoology, a crepuscular animal is one that is active primarily during the twilight period, [1] 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.
A number of factors affect the time of day an animal is active. Predators hunt when their prey is available, and prey try to avoid the times when their principal predators are at large. The temperature may be too high at midday or too low at night. [2] Some creatures may adjust their activities depending on local competition.
The word crepuscular derives from the Latin crepusculum ("twilight"). [3] Its sense accordingly differs from diurnal and nocturnal behavior, which respectively peak during hours of daylight and darkness. The distinction is not absolute, because crepuscular animals may also be active on a bright moonlit night or on a dull day. Some animals casually described as nocturnal are in fact crepuscular. [2]
Special classes of crepuscular behaviour include matutinal, or "matinal", animals active only in the dawn, and vespertine, only in the dusk. Those active during both times are said to have a bimodal activity pattern.
The various patterns of activity are thought to be mainly antipredator adaptations, though some could equally well be predatory adaptations. [4] Many predators forage most intensively at night, whereas others are active at midday and see best in full sun. The crepuscular habit may both reduce predation pressure, increasing the crepuscular populations, and offer better foraging opportunities to predators that increasingly focus their attention on crepuscular prey until a new balance is struck. Such shifting states of balance are often found in ecology.
Some predatory species adjust their habits in response to competition from other predators. For example, the subspecies of short-eared owl that lives on the Galápagos Islands is normally active during the day, but on islands like Santa Cruz that are home to the Galapagos hawk, the owl is crepuscular. [5] [6]
Apart from the relevance to predation, crepuscular activity in hot regions also may be the most effective way of avoiding heat stress while capitalizing on available light.
Crepuscular flight activity is preferred by some animals, such as the walnut twig beetle, due to warmer temperatures, moderate wind speeds, and low barometric pressure. [7]
Crepuscular activity can be influenced by the lunar cycle due to the change in nocturnal light. This creates changes in animal sleep, reproduction, and foraging behaviours, often becoming less active during periods of low light. [8]
Animal patterns of activity sometimes change during migration due to changes in environmental conditions. Mule deer are crepuscular, but they are only active at sunset before and during migration. In the spring they are only active at sunrise because the snow is at its hardest, so it is easier for the deer to move without sinking in the snow. [9]
During migration, some types of swallow are active primarily during daytime hours with some activity during twilight hours. [10]
Crepuscular animal activity is affected by human activity, because humans are diurnal. Crepuscular animals are less likely to participate in typical foraging or reproductive behaviors and deal with increased stress and mortality rates when humans are present. [11] Animals may change their usual activity patterns in response to the presence of humans. For example, Asian black bears may avoid areas with high human activity during the day, but go to these locations during twilight or nighttime hours. [12]
Light pollution impacts crepuscular behaviour because it mimics natural light conditions, leading crepuscular animals to behave as they would on nights with more moonlight. [8]
Many familiar mammal species are crepuscular, including the endangered Amazon river dolphin, some species of bats, [2] hamsters, humans, housecats, stray dogs, [13] rabbits, [2] ferrets, [14] rats, [15] jaguars, ocelots, bobcats, servals, strepsirrhines, red pandas, bears, [16] deer, [2] [17] moose, sitatunga, capybaras, chinchillas, the common mouse, skunks, squirrels, foxes, wombats, wallabies, quolls, possums [2] and marsupial gliders, tenrecs, and spotted hyenas.
Snakes, lizards, and frogs, [18] especially those in desert environments, may be crepuscular. [2]
Crepuscular birds include the common nighthawk, barn owl, [19] owlet-nightjar, chimney swift, American woodcock, spotted crake, white-breasted waterhen, [20] European nightjars, [8] and common buzzards. [21]
Many moths, beetles, flies, and other insects are crepuscular and vespertine.[ citation needed ]
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".
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.
The common degu, or, historically, the degu, is a small hystricomorpha rodent endemic to the Chilean matorral ecoregion of central Chile. The name degu on its own indicates either the entire genus Octodon or, more commonly, just the common degu. Common degus belong to the parvorder Caviomorpha of the infraorder Hystricognathi, along with the chinchilla and guinea pig. The word degu comes from the indigenous language of Chile, Mapudungun, and the word dewü, meaning 'mouse' or 'rat'.
An endotherm is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism, such as within brown adipose tissue.
Biological rhythms are repetitive biological processes. Some types of biological rhythms have been described as biological clocks. They can range in frequency from microseconds to less than one repetitive event per decade. Biological rhythms are studied by chronobiology. In the biochemical context biological rhythms are called biochemical oscillations.
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.
Vespertine is a term used in the life sciences to indicate something of, relating to, or occurring in the evening. In botany, a vespertine flower is one that opens or blooms in the evening. In zoology, the term is used for a creature that becomes active at dusk, such as bats and owls. Strictly speaking, however, the term means that activity ceases during the hours of full darkness and does not resume until the next evening. Activity that continues throughout the night should be described as nocturnal.
Deilephila elpenor, the elephant hawk moth or large elephant hawk moth, is a moth in the family Sphingidae. Its common name is derived from the caterpillar's resemblance to an elephant's trunk. It is most common in central Europe and is distributed throughout the Palearctic region. It has also been introduced in British Columbia, Canada. Its distinct olive and pink colouring makes it one of the most recognisable moths in its range. However, it is quite easy to confuse the elephant hawk moth with the small elephant hawk moth, a closely related species that also shares the characteristic colours.
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.
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.
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" comes from Latin: diēs, lit. 'day', and refers to a 24-hour period. The migration occurs when organisms move up to the uppermost layer of the water at night and return to the bottom of the daylight zone of the oceans or to the dense, bottom layer of lakes during the day. DVM is important to the functioning of deep-sea food webs and the biologically-driven sequestration of carbon.
The Azores noctule is a species of bat found in the dry forests of the Azores. It is the only species of mammal endemic to the Azores. It has been recorded on most of the islands of the Azores, and remains common on some but is rare on others. Its numbers are threatened due to habitat loss caused by humans, and the remaining populations are quite fragmented. It is known to roost in hollowed-out trees, buildings, and caves.
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 crepuscular animals that are significantly active during the predawn or early morning hours. During the morning twilight period and shortly thereafter, these animals partake in important tasks, such as scanning for mates, mating, and foraging.
Vision is the most important sense for birds, since good eyesight is essential for safe flight. Birds have a number of adaptations which give visual acuity superior to that of other vertebrate groups; a pigeon has been described as "two eyes with wings". Birds are theropod dinosaurs, and the avian eye resembles that of other reptiles, with ciliary muscles that can change the shape of the lens rapidly and to a greater extent than in the mammals. Birds have the largest eyes relative to their size in the animal kingdom, and movement is consequently limited within the eye's bony socket. In addition to the two eyelids usually found in vertebrates, bird's eyes are protected by a third transparent movable membrane. The eye's internal anatomy is similar to that of other vertebrates, but has a structure, the pecten oculi, unique to birds.
Distraction displays, also known as diversionary displays, or paratrepsis are anti-predator behaviors used to attract the attention of an enemy away from something, typically the nest or young, that is being protected by a parent. Distraction displays are sometimes classified more generically under "nest protection behaviors" along with aggressive displays such as mobbing. These displays have been studied most extensively in bird species, but also have been documented in populations of stickleback fish and in some mammal species.
Chapman's zebra, named after explorer James Chapman, is a subspecies of the plains zebra from southern Africa.
Whether fish sleep or not is an open question, to the point of having inspired the title of several popular science books. In birds and mammals, sleep is defined by eye closure and the presence of typical patterns of electrical activity in the brain, including the neocortex, but fish lack eyelids and a neocortex. Some species that always live in shoals or that swim continuously are suspected never to sleep. There is also doubt about certain blind species that live in caves.
The nocturnal bottleneck hypothesis is a hypothesis to explain several mammalian traits. In 1942, Gordon Lynn Walls described this concept which states that placental mammals were mainly or even exclusively nocturnal through most of their evolutionary history, from their origin 225 million years ago to after the Cretaceous–Paleogene extinction event, 66 million years ago. While some mammal groups later adapted to diurnal (daytime) lifestyles to fill newly unoccupied niches, the approximately 160 million years spent as nocturnal animals has left a lasting legacy on basal mammalian anatomy and physiology, and most mammals are still nocturnal.