These creatures have evolved unique ways to stay awake and alert, even when their bodies are at rest.
They are able to stay awake and alert by shutting down only half of their brain at a time.
Scientists believe that bullfrogs may enter a state of deep rest that is similar to sleep but they do not go into full REM sleep.
Alpine swifts are small birds that can fly for months on end without landing. They are able to do this by entering a state of deep rest while they are flying.
Bluefish are predatory fish that are constantly swimming. They never sleep because they need to keep moving to get enough oxygen.
Jellyfish are another type of simple animal that does not need to sleep. They have a decentralized nervous system which means that they do not have a central brain.
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