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Concept
Nocturnality
Summary
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed senses of hearing, smell, and specially adapted eyesight. 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 with their body size to compensate for the lower light levels at night. More specifically, they have been found to have a larger cornea relative to their eye size than diurnal creatures to increase their : in the low-light conditions. Nocturnality helps wasps, such as Apoica flavissima, avoid hunting in intense sunlight.
Diurnal animals, including humans (except for night owls), squirrels and songbirds, are active during the daytime. Crepuscular species, such as rabbits, skunks, tigers and hyenas, are often erroneously referred to as nocturnal. Cathemeral species, such as fossas and lions, are active both in the day and at night.
While it is difficult to say which came first, nocturnality or diurnality, a hypothesis in evolutionary biology, the nocturnal bottleneck theory, postulates that in the Mesozoic, 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 is not needed anymore due to the evolution of compensatory sensory systems, such as a heightened sense of smell and more astute auditory systems. In a recent study, recently extinct elephant birds and modern day nocturnal kiwi bird skulls were examined to recreate their likely brain and skull formation.
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