
A
bat illustrating nocturnal features.
As an
animal behavior, 'nocturnality' describes
sleeping during the
daytime and being active at
night - the opposite of the
diurnal human lifestyle, and that of those animals with which we are most familiar. The intermediate
crepuscular schedule (twilight activity) is also common. Some species are active both during the day and night. Living at night can be seen as a form of
niche differentiation, where a species' niche is partitioned not by resources but by
time itself, i.e. temporal division of the
ecological niche. It can also be viewed as a form of
crypsis, in other words an adaptation to avoid or enhance
predation. There are other reasons for nocturnality as well, such as keeping out of the heat of the day. This is especially true in
deserts, where many animals' nocturnal behavior prevents it from losing precious water during the hot, dry daytime. This is an
adaptation that enhances
osmoregulation.
[1]
Many species which are otherwise diurnal exhibit some nocturnal behaviour; for example, many
seabirds and
sea turtles attend breeding sites or colonies nocturnally to reduce the risk of predation (to themselves or their offspring) but are otherwise diurnal.
Nocturnal animals generally have highly developed senses of
hearing and
smell, and specially adapted
eyesight. In
zoos, nocturnal animals are usually kept in special night-illumination enclosures to reverse their normal
sleep-wake cycle and to keep them active during the hours when visitors will be attempting to see them.
Some animals, such as
cats, have eyes that can adapt to both night and day levels of illumination. Others, e.g.
bushbabies and
bats, can only function at night.
A person who exhibits nocturnal habits is referred to as a
night owl.
Examples

A long
exposure outside a floodlight showing moth movements.
The following animals are generally classified as nocturnal:
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Aye-aye
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Badger
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Cat
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Centipedes
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Civet
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Cockroaches
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College Student
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Flying squirrels
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Fox
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Giant White-tailed Rat
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Green Sea Turtle
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Hedgehog
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Hyena
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Kangaroo rats
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Kiwi
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Lion
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Lumholtz's Tree-kangaroo
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Moths
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Nightjars
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Oilbird
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Owls
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Potto
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Raccoon
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Red-legged Pademelon
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Skunk
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Sugar glider
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Tiger
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Tree frogs
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Western harvest mouse
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Whippoorwill
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Wombats
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Wolf
References
1. N.A.Campbell (1996) ''Biology'' (4th edition) Benjamin Cummings NY. ISBN 0-8053-1957-3
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The Nocturnal Society