Why do dolphins sleep with one eye open?
Show answer & explanation
Answer: Half brain stays awake
Saltwater irritates closed eyes — Wrong. Saltwater doesn't irritate dolphin eyes—they're perfectly adapted to ocean water. The open eye is controlled by the awake brain hemisphere during unihemispheric sleep.
Half brain stays awake ✓ — Correct! Dolphins use 'unihemispheric sleep' where one brain hemisphere sleeps while the other stays awake. This allows them to breathe consciously (they can't breathe automatically like us), watch for threats, and maintain pod contact. They switch sides every 2 hours!
Their eye muscles don't fully relax — Wrong. Dolphin eye muscles work perfectly fine! The open eye is controlled by the awake brain hemisphere—it's a neurological phenomenon, not a muscle problem. They can close both eyes when fully awake.
More Animal Behavior questions
- Why can the same soft barn-owl feathers that mute flight make rainy hunting worse?
- Why is silent flight useful even if a mouse never hears the owl coming?
- Besides ordinary airflow noise, what sound can the velvety surface on owl flight feathers help reduce?
- At high wing angles, why can the comb-like feathers on an owl's leading edge make airflow quieter?
- What lets a barn owl glide slowly and quietly, apart from its fringed, velvety feathers?
- Male platypuses have venomous ankle spurs. Why are they probably not mainly prey-hunting tools?