Сумеречная активность животных: экология и поведение.

Animal behavior primarily characterized by activity during the twilight
the atmospheric optical effect

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. 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. Some creatures may adjust their activities depending on local competition.

The word crepuscular derives from the Latin crepusculum ("twilight"). 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. 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. 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. 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. During migration, some types of swallow are active primarily during daytime hours with some activity during twilight hours.

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. 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. Light pollution impacts crepuscular behaviour because it mimics natural light conditions, leading crepuscular animals to behave as they would on nights with more moonlight. rabbits, rats, jaguars, ocelots, bobcats, servals, strepsirrhines, red pandas, bears, deer, moose, sitatunga, capybaras, chinchillas, the common mouse, skunks, squirrels, foxes, wombats, wallabies, quolls, possums especially those in desert environments, may be crepuscular. owlet nightjar, chimney swift, American woodcock, spotted crake, white breasted waterhen, European nightjars, and common buzzards. Many moths, beetles, flies, and other insects are crepuscular and vespertine. For example, Coprophanaeus ensifer, a South American necrophagous beetle, is most active during at dusk and dawn.