Nictitating Membrane

Great Horned Owl

When I think of great horned owls (Bubo virginianus) a picture of a ghostly figure peering  down from the high rafters of a barn comes to mind. Great horned owls are primarily nocturnal, hunting mostly from dusk to dawn. However, they will also hunt during the day. These magnificent birds do not only secret themselves in dark, secluded, sheltered areas during daylight, they often roost on tree branches in bright sunlight. Because of my ingrained vision of great horned owls as nocturnal creatures who hide during the day,  when I see one in bright sunlight it is always a surprise.

Great horned owls have three eyelids. Two resemble usual eyelids. The upper one closes completely over the eye when the bird blinks. The second comes up when the bird sleeps. The third eyelid (called the nictitating membrane) is used to moisturize and clean the eye. The nictitating membrane  also protects the owl eye from brightness, foreign objects and damage while feeding chicks. In great horned owls nictitating membranes are thin layers of translucent tissue. They close diagonally across the entire eye from the inside to the outside.

Leonard and I found this great horned owl roosting about noon in an Oregon ash located between the North and South Elkins Barns at Ash Creek Wildlife Area in the center of Big Valley CA (Modoc and Lassen Counties CA).

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1 Response to Nictitating Membrane

  1. Lin Erickson says:

    Great find…you have been very patient with this one!

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