We all love owl eyes, but did you know they have some very unique features? I’ve posted about their special eyeballs before, but what about eyelids?

All birds have three eyelids – like humans, they have an upper and lower eyelid. Owls are among the only birds that have a larger upper eyelid than lower eyelid. They are the only birds that blink like humans, by dropping their upper eyelids. But when owls sleep, they close their eyes the way other birds do—by raising the lower lids.

Beneath the two outer eyelids birds have a translucent nictitating membrane, sometimes called a “third eyelid.” This membrane sweeps across the cornea from the inside corner of the eye to the outer edge of the eye. It moistens and cleans the cornea, especially in flight. It is also drawn across the eye when there is a chance the eye might be scratched or damaged such as when capturing prey, flying through brush or feeding their young.

In summation, one could say that owls have three eyelids for each eye: one for blinking (upper), one for sleeping (lower), and one for keeping their eyes clean and protected (nictitating).

Copied from Naturally Curious)

  • someguy3English
    11·
    1 year ago

    Have scratched my eye. Would not recommend. Would recommend third eyelid for next iteration of human.

    • anon6789@lemmy.worldOP
      5·
      1 year ago

      Youch! I hope it was able to heal.

      I wear hard contacts and if they go on without enough solution and they suction on there it hurts like heck until I can get them out

      If one would consider developing safety glasses part of our evolution, we’re still ahead of the membraned animals. Some of them can supposedly survive a pellet gun shot. We just lose out on having them always on our face.

      We may have had one once upon a time though! From Wikipedia:

      Fully developed nictitating membranes are found in fish, amphibians, reptiles, birds and mammals, but are rare in primates. In humans, the plica semilunaris (also known as the semilunar fold) and its associated muscles are homologous to the nictitating membranes seen in some other mammals and other vertebrates. In most primate species, a plica semilunaris is generally not present, although fully developed nictitating membranes can be found in lemurs and lorisoid primates. Some mammals, such as camels, polar bears, seals and aardvarks, have full nictitating membranes, and many mammals retain a small, vestigial portion of the membrane in the corner of the eye.