A special thank you to reader Dr. Barbara Goodman, Professor of Physiology at Sanford School of Medicine of the University of South Dakota who sent me a story from The Scientist about sleep in animals complete with footage of a dolphin that was seen apparently "sleeping" (video posted on YouTube):
Why do animals sleep? This is a question with many potential answers. It is known that birds and mammals experience slow-wave and rapid eye movement (REM) sleep patterns. During the first pattern, slow waves with high amplitudes can be seen if measuring electrical activity (EEG) in the cortex. Respiration and heart rate also slow down and have a regular rhythm. REM sleep on the other hand is characterized by electrical activity patterns that look similar to those seen when a person is awake. During this pattern eye movements are seen (hence the name) along with more variability in both respiration and heart rate.
Other animals undergo periods of rest characterized by slowed, regular respiration and heart rates along with decreased sensitivity to stimuli in their environment, such as fish and insects. Some animals experience what is called unihemispheric sleep in which only half their brain dozes at a time (marine animals, some birds). Think of how much we could accomplish if we could do that!
Whether we nap (like a giraffe or elephant only needing 4 hours of sleep) or doze all day (like a big brown bat that needs to 20 hours per day, or a teenager), it appears that sleep is important for many animals.
Diet may be related to how much sleep we need as herbivores eat more often and sleep less than carnivores (think lion after eating a meal). Sleep is a way to conserve energy (think hibernating animals and pre-industrial humans that slept during the coldest times of the night). Evidence from studies of mammals and birds also support the importance of sleep for forming memories and processing information. Some think that migratory birds may even experience unihemispheric sleep or slow-wave sleep involving both hemispheres during flight.
Sleep is apparently not unique to vertebrates as studies report sleep-like patterns and behaviors in fruit flies, honeybees, cockroaches as well as scorpions.
See the full article for more fun sleep facts in animals: The Scientist