Crepuscular animal
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.
For the atmospheric optical effect, see crepuscular rays.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.
Etymology and usage[edit]
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.
Migration[edit]
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]
Human impact on crepuscular behaviour[edit]
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]