Question: which group experiences the highest level of rem sleep

title: Rapid eye movement sleep
text: Although it manifests differently in different animals , REM sleep or something like it occurs in all land mammals as well as in birds . The primary criteria used to identify REM are the change in electrical activity , measured by EEG , and loss of muscle tone , interspersed with bouts of twitching in phasic REM . The amount of REM sleep and cycling varies among animals ; predators enjoy more REM sleep than prey . Larger animals also tend to stay in REM for longer , possibly because higher thermal inertia of their brains and bodies allows them to tolerate longer suspension of thermoregulation . The period ( full cycle of REM and non-REM ) lasts for about 90 minutes in humans , 22 minutes in cats , and 12 minutes in rats . In utero , mammals spend more than half ( 50 -- 80 % ) of a 24 - hour day in REM sleep . 

Answer: answer: Predators enjoy more REM sleep than prey and larger animals tend to stay in REM for longer. In utero, mammals spend more than half (50-80 %) of a 24-hour day in REM sleep.