Dolphins: Half The Brain Stays Awake
Dolphins literally sleep with one eye open. One hemisphere of the brain rests while the other stays alert, allowing them to breathe, swim, and watch for predators. A landmark study in PLOS ONE found dolphins could maintain this state with no cognitive decline for 15 continuous days.
Sperm Whales: Sleeping Upright In The Ocean
Sperm whales do something almost no other animal does: they sleep vertically, heads up and tails down, bobbing just below the surface in complete stillness. Research published in Current Biology confirmed this through suction cup tags and found a group so deeply asleep they didn’t react to a vessel that bumped into them.
<img src="https://img.etimg.com/thumb/msid-132576422,width-640,height-480,resizemode-75,imgsize-171033/<a href="https://abs<a href="https://absafricatv.com/europe-africa-market-update-23-july/” title=”Europe & Africa Market Update 23 July”>africatv.com/africa-at-au-extraordinary-summit/” title=”Africa: At AU Extraordinary Summit”>african-elephants-the-worlds-shortest-sleepers.jpg” alt=”African Elephants: The World’s Shortest Sleepers”>
African Elephants: The World’s Shortest Sleepers
The largest land animal on Earth sleeps the least of any mammal. Wild African elephants average just two hours of sleep a day, often going 46 hours without any sleep at all. A PLOS ONE study tracking wild matriarchs in Botswana found they experienced REM sleep only once every three to four days.
Common Swifts: Ten Months Without Landing
The common swift spends nearly its entire non-breeding life in the air: eating, mating, and sleeping on the wing. A 2016 study in Current Biology tracked swifts using accelerometers and found some individuals stayed airborne for 10 months continuously, suggesting they sleep while gliding on thermal currents.
Great Frigatebirds: Sleeping Mid-Flight Over The Ocean
Frigatebirds can’t land on water and sometimes fly for weeks at a stretch over the open ocean. A study in Nature Communications recorded their EEG during flight and found they sleep with one hemisphere at a time, or occasionally both, for just 41 minutes per day while airborne.
Swainson’s Thrush: Micro-Naps Of A Few Seconds
This migratory songbird flies thousands of miles at night and barely sleeps during migration season. Instead, it takes hundreds of micro-naps during the day, each lasting just seconds. A study in Animal Behaviour found these birds use unihemispheric sleep during naps, closing one eye at a time to compensate for their nighttime exertion.
Little Brown Bats: Nearly 20 Hours Of Sleep A Day
At the opposite extreme sits the little brown bat, which sleeps close to 20 hours every single day. Most of this is torpor, a state where body temperature drops and metabolism almost shuts down to conserve energy. Oxford Academic’s journal Sleep notes this extreme duration has made bats a key reference species in comparative sleep science globally.
(Disclaimer: This story is for educational purposes alone.)
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