Animals That Sleep With One Eye Open

Animals That Never Fully Sleep Radiocity By Radiocity Team Published Jul 22, 2025 [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

Dolphins They rest one half of their brain while the other stays alert, surfacing to breathe and avoiding predators mid-sleep. [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

Fur Seals When at sea, fur seals exhibit unihemispheric sleep—one brain side sleeps while the other helps them stay balanced and aware. [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

Mallard Ducks Outer ducks in a flock sleep with one eye open, keeping watch for threats while inner ducks rest fully. [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

Crocodiles They’ve been observed sleeping with one eye open, possibly keeping part of their brain active to monitor nearby movement. [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

Frigatebirds These seabirds sleep mid-flight with one eye open, resting only one hemisphere of the brain at a time. [{ "selector": ".custom-gradient", "duration": "500ms", "fill": "forwards", "keyframes": [ { "offset": 0, "transform": "translateY(100px)" }, { "offset": 1, "transform": "translateY(0)" } ] }]

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