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Sleep can follow a physiological or behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone (possibly with some exceptions; see below regarding the sleep of birds and of aquatic mammals), and a compensatory increase following deprivation of the state, this last known ...
Crepuscular, a classification of animals that are active primarily during twilight, making them similar to nocturnal animals. Diurnality, plant or animal behavior characterized by activity during the day and sleeping at night. Cathemeral, a classification of organisms with sporadic and random intervals of activity during the day or night.
Porcupines are nearsighted and slow-moving. They are mainly active at night (nocturnal); on summer days, they often rest in trees. They do not hibernate, but sleep in and stay close to their dens in winter. The strength of the porcupine's defense has given it the ability to live a solitary life, unlike many herbivores, which must move in flocks ...
Cats conserve energy by sleeping more than most animals, especially as they grow older. The daily duration of sleep varies, usually between 12 and 16 hours, with 13 and 14 being the average. Some cats can sleep as much as 20 hours. The term "cat nap" for a short rest refers to the cat's tendency to fall asleep (lightly) for a brief period.
Birds have one of the most complex respiratory systems of all animal groups. [77] Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs.
In birds, perch height is believed to play a significant role in sleep; lower perch height has been shown to reduce the number and length of REM sleep episodes in pigeons, and a higher perch increases REM sleep and decreases slow-wave sleep. [6] Findings also suggest that the time spent awake by pigeons increases when nesting on lower perches.
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[6] [4] Light seems to have therapeutic antidepressant effects when an organism is exposed to it at appropriate times during the circadian rhythm, regulating the sleep-wake cycle. [ 6 ] [ 4 ] In addition to mood, learning and memory become impaired when the circadian system shifts due to light stimuli, [ 6 ] [ 20 ] which can be seen in studies ...