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| Which Animals | Dreaming | Observing a Cat or Dog | Observing Other Animals |
Not all animals experience REM sleep, but some do. The amount of REM sleep an animal gets seems to be related to its safety in its environment. The more danger for the animal, the less REM sleep. The amount of REM sleep is also related to how developed the animal is at birth. Animals born fairly mature, such as sheep (whose REM Sleep is only 1% of their daily sleep), have less REM sleep than animals that continue to grow and develop more after they are born, such as humans.
Amphibians and Fish have never been found to have any similar experience to REM sleep (1).
Birds spend about 5% of their sleep time in REM sleep. They seem to have very brief dreaming episodes. (2)
Most Mammals experience REM sleep. Ruminating animals, animals that chew their cud, get very little (if any) REM sleep.
Reptiles have rapid eye movements during sleep, but they are not accompanied with brain waves similar to those of humans during REM sleep. This partial REM sleep may be a clue in the evolution of REM sleep and dreaming.
Not all animals that experience REM sleep dream. Some think that perhaps only mammals seeming to be more advanced in thinking than others dream during REM sleep. However, dolphins, thought to be highly intelligent do not have any REM sleep whatsoever! Dreaming mammals besides humans include: cats, dogs, chimpanzees, horses, cows.
Cats and dogs have dreaming periods usually about 15 minutes into their sleep.(3) Their REM sleep is easy to observe. Simple indicators are movements under the eyelids, changes in breathing patterns, twitching of the ears or whiskers, or occasional spasms or jerks of the face. They may even make running motions with their paws. If someone placed food before a sleeping dog's nose, the dog may even start chewing.
Chimpanzees have howled during sleep.
Elephants don't change in posture when entering or exiting REM sleep. Therefore, it is often difficult to tell if they are in NonREM or REM sleep. It is hard to see the eye movements since their eyes are relatively small. However, some indicators of REM sleep in elephants, as well as other animals, are twitches, vocalizing and irregular breathing. (1)
Giraffes have about 20 min. of REM sleep each night in episodes of 1-6 minutes each. During this time, they lie down, heads resting over their bodies or on the ground. They with occasional twitches. (1)
Horses, which must lie down to experience REM sleep, sometimes move their legs while sleeping, and will even neigh in their sleep.
Sheep, who often sleep in a "sphinx-like" position occasionally stretch out while sleeping. During this time, they experience many REM sleep-like if not REM-sleep indicators. During this time, they have eye movements and ears and legs occasionally twitch. (1)
(1) Sleep CD
(2) Hartman, Ernest. "Sleep," The Worldbook Encyclopedia (Vol. 17). Chicago: World Book, Inc. 1990, pp. 507-508.
(3) Coren, Stanley. Sleep Thieves: an Eye-Opening Exploration into the Science & Mysteries of Sleep. New York: The Free Press, 1996. p. 43[an error occurred while processing this directive]