Birds experience the same cycles of slow-wave sleep and rapid eye movement (REM) sleep that humans do—patterns of brain activity that scientists believe play a crucial role in the growth of big brains, theirs and ours. Birds rarely have REM sleep longer than ten seconds, packaged into hundreds of episodes per sleep period, while humans have several bouts of REM sleep per night, each lasting ten minutes to an hour. But for both mammals and birds, REM sleep may be especially important for the early development of the brain. Newborn mammals such as kittens have much more REM sleep than adult
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