Owls exhibit a unique adaptation where one eye remains open to stay vigilant during rest, an attribute essential for their nocturnal hunting.
Dolphins engage in unihemispheric sleep, shutting down one brain hemisphere while the other remains active, allowing them to keep an eye open for potential threats.
Waterfowl like ducks and geese can sleep with one eye open, enabling them to detect predators while in a semi-restful state
Some species of frogs have transparent eyelids, permitting them to rest with an observant eye for any lurking danger.
Certain fish, like the parrotfish, nap with their eyes open to ensure protection from predators while they doze among coral reefs.
Meerkats, known for their lookout behaviors, often sleep with one eye open to ensure the safety of their pack.
Chameleons manage to snooze with one eye open, maintaining a watchful stance even during slumber
Lizards, such as the green iguana, employ open-eyed sleeping to remain vigilant against potential threats in their surroundings.