5 animals with the most fascinating sleep habits

2. Ducks: One half of the brain sleeps at a time

Many duck species have mastered unihemispheric slow-wave sleep, in which one hemisphere sleeps while the other remains awake. The open eye keeps watch for predators while the sleeping half of the brain gets the rest it needs. Ducks positioned on the outer edge of a flock remain more alert than those safely tucked into the middle, showcasing an impressive survival strategy.

3. Sea otters: Sleeping while holding hands

Sea otters often sleep floating on their backs in coastal waters. To keep from drifting apart in strong currents, they often hold paws or wrap themselves in kelp, which acts as a natural anchor. This behaviour helps family groups stay together while they rest and prevents individuals from drifting into dangerous open waters.

4. Sperm whales: Vertical power naps

Sperm whales have one of the most unusual sleeping postures in the animal kingdom. They often sleep almost motionless in an upright, vertical position, with their heads pointing toward the surface. These naps usually last less than 20 minutes and occur close to the water’s surface.

 

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5. Freshwater turtles: The surprising “butt breathing” sleepers

Some freshwater turtles, including Australia’s Fitzroy River turtle and Murray River turtle, spend long periods underwater during winter hibernation. While asleep, they dramatically reduce their metabolism and obtain much of the oxygen they need through cloacal respiration—absorbing oxygen-rich water through specialised sacs connected to the cloaca, an opening at the rear of the body. Although popularly described as “breathing through their bums,” the process is actually a sophisticated adaptation that enables the turtles to remain submerged for weeks or even months without regularly surfacing for air.