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I've had several pet birds and I've observed the same thing from them. I just assumed they were just pretending to sleep.

• yareally 10y ago
  Your comment made me wonder how common it is with birds and it seems to be trait shared with all of them[1]. Pretty interesting. I asked my friend if her bird does that and it only seems to when it's not in a deep sleep yet, but eventually it will close both eyes. [1] https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
  • throwaway98764 10y ago
    Gives a new meaning to the term, "sleep with one eye open at night." :)
    • glandium 10y ago
      Let me venture a guess: that expression comes exactly from observing animals keeping one eye open.