Look upcrepuscular in Wiktionary, the free dictionary.
Inzoology, acrepuscularanimal is one that is active primarily during thetwilight period,[1] beingmatutinal (active during dawn),vespertine/vespertinal (active during dusk), or both. This is distinguished fromdiurnal andnocturnal behavior, where an animal is active during the hours ofdaytime and ofnight, respectively. Some crepuscular animals may also be active bymoonlight or during anovercast day.
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 wordcrepuscular derives from theLatincrepusculum ("twilight").[3] Its sense accordingly differs from diurnal and nocturnal behavior, which respectively peak during hours of daytime and night. 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 mainlyantipredator adaptations, though some could equally well be predatoryadaptations.[4] Many predatorsforage 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 ofshort-eared owl that lives on theGalápagos Islands is normally active during the day, but on islands likeSanta Cruz that are home to theGalapagos 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 thewalnut twig beetle, due to warmer temperatures, moderate wind speeds, and low barometric pressure.[7]
Crepuscular activity can be influenced by thelunar cycle due to the change in nocturnal light. This creates changes in animalsleep,reproduction, andforaging behaviours, often becoming less active during periods of low light.[8]
Animal patterns of activity sometimes change duringmigration due to changes in environmental conditions.Mule deer are crepuscular, but they are only active atdusk before and during migration. In thespring they are only active atdawn because thesnow is at itshardest, so it is easier for the deer to move without sinking in the snow.[9]
During migration, some types ofswallow are active primarily during daytime hours with some activity during twilight hours.[10]
Crepuscular animal activity is affected byhuman activity, because humans are diurnal. Crepuscular animals are less likely to participate in typical foraging or reproductive behaviors and deal with increasedstress andmortality rates when humans are present.[11] Animals may change their usualactivity 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]
^Merck, John."The community of terrestrial animals".Field Studies II: The Natural History of the Galápagos Islands. University of Maryland Department of Geology. Archived fromthe original on 23 June 2012. Retrieved15 January 2012.
