While many animals can hold their breath underwater, hippos are a notable example of animals that can actually sleep underwater.
How Hippos Sleep Underwater
Hippos possess a remarkable adaptation that allows them to doze off submerged. They use an automatic breathing reflex. This means that even when asleep, the hippo's body will instinctively rise to the surface to take a breath, then sink back down, all without the hippo fully waking up. This is a truly fascinating adaptation for these large mammals!
Other Animals That Can Sleep Underwater (Partially)
Although hippos are a prime example, other aquatic animals also exhibit the ability to rest or sleep underwater, often in specialized ways:
- Dolphins and Whales: These marine mammals only sleep with half their brain at a time (unihemispheric sleep), allowing the other half to remain alert for breathing and vigilance against predators. This is more of a resting state than a deep sleep.
- Sea Otters: Sea otters sometimes wrap themselves in kelp to avoid drifting away while they rest underwater.
- Crocodiles: Crocodiles can stay submerged for extended periods, and while they don't truly "sleep" in the way humans do, they enter a resting state underwater.
- Frogs: Some frog species hibernate underwater during the winter, slowing their metabolism and absorbing oxygen through their skin.
