Falcon Cam Partners

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1. Monday, April 5, 2010

   Do Birds Blink?

   The summer-like temperatures of 89 degrees in Richmond today seem to have made the female a bit drowsy. We can see her eyes slowly closing. Birds eyelids function much the same way ours do, closing to protect the eye and block out light. Unlike our eyes, a bird’s upper eyelid is relatively immobile and the lower lid moves up to close the eye.

   Birds (and many other animals) actually have a “third eyelid” called a nictitating membrane. As you can see in the video below the nictating membrane sweeps from front to back, cleaning and moistening the eye. This membrane is translucent, allowing birds to retain some vision even while cleaning or protecting the eye. This is as important as closing their eyes during flight could be very risky. This is especially true for birds like peregrine falcons whose stoops (steep dives over prey) can reach speeds of up to 200 miles per hour. A peregrine falcon’s nictitating membrane is relatively transparent as compared to other birds, allowing them to track prey even with it covering the eye.