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Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. The common adjective is "nocturnal". Nocturnal creatures generally have highly developed senses of hearing, smell, and specially adapted eyesight. Such traits can help animals such as the ''Helicoverpa zea'' moths avoid predators.〔Agee, H. R., and E. Orona. "Studies of the neural basis of evasive flight behavior in response to acoustic stimulation in Heliothis zea (Lepidoptera: Noctuidae): organization of the tympanic nerves". ''Annals of the Entomological Society of America'' 81.6 (1988): 977–985〕 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 to their body size in order to compensate for the lower light levels during the night. More specifically, these animals have been found to have a larger cornea relative to their eye size than diurnal creatures, in order to increase their visual sensitivity in the low light conditions. Nocturnality helps wasps such as ''Apoica flavissima'' avoid hunting in intense sunlight. Diurnal animals, including squirrels and songbirds, are active during the daytime. Crepuscular species, such as rabbits, skunks, cats, and hyenas, are often erroneously referred to as nocturnal. Cathemeral species, such as fossas and lions, are active both day and night. While most humans are diurnal, for various personal and social/cultural reasons some people are temporarily or habitually nocturnal. The most known creatures to be nocturnal include cats, rodents, and owls, which all have heightened senses (including sense of sight). ==Origins== While it is difficult to say which came first, nocturnality or diurnality, there is a leading hypothesis out in the evolutionary biology community. Known as the "bottleneck theory", it postulates that millions of years ago in the Mesozoic era, many ancestors of modern day mammals evolved nocturnal characteristics in order to avoid contact with the numerous diurnal predators. 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 isn't needed anymore due to the evolution of compensatory sensory systems, such as a heightened sense of smell and more astute auditory systems. The anomaly to this theory were anthropoids, who appeared to have the most divergence from nocturnality than all organisms examined. While most mammals didn't 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nocturnality」の詳細全文を読む スポンサード リンク
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