In the Blink of an Eye

It is not only fine feathers that make fine birds.

~Aesop

Tricolored Heron head close up

Tricolored Heron head close up (click on photos to enlarge)

The eyes of birds are magical, so intense, so bright, so focused. One of the great things about my trip to Florida was being able to be close to a variety of birds, close enough to appreciate and capture their beauty, and close enough to look into their eyes (at least through a telephoto lens).

Snowy Egret swallowing goby close up

Snowy Egret swallowing goby

When I was looking at images for the last post on the birds of Huntington Beach State Park, I noticed the eye of the Snowy Egret. You can see the clear membrane covering about half of the bird’s eyeball. That is the nictitating membrane (from Latin nictare, to blink), a thin membrane that helps protect the eye of birds and a few other groups of animals. This so-called “third eyelid” is also found in various reptiles, mammals, and fishes. In all cases, the membrane serves as a protective adaptation when it is drawn across the eye.

Sandhill Crane eye

Sandhill Crane eye

Sandhill Crane nicitating membrane

Sandhill Crane with nictitating membrane pulled across eye

The membrane rests at the front edge of the eye and sweeps backward to clean and moisten the cornea. When pulled across the eyeball, the membrane still allows a bird to see due to its transparent (or at least translucent) nature, although it is apparently more opaque in certain species such as owls. And I learned that we, too, have a nictitating membrane in our eyes – it is that little crescent-shaped piece of pinkish skin in the corner of our eye nearest the nose. It is called the plica semilunarisours, but is vestigial and no longer functions as it does in birds.

White Ibis eye 1

White Ibis eye

White Ibis nicitating membrane

White Ibis eye showing nictitating membrane

While the nictitating membrane is especially important in birds as they fly, dive underwater, or feed anxious chicks with sharp beaks, it is also used as their primary blinking mechanism. The lower eyelid closes when a bird sleeps, but they typically blink using this third eyelid. Being able to closely watch so many different types of birds while I was in Florida gave me ample opportunity to appreciate how frequently birds blink their incredible eyes.

Glossy Ibis with nictitating membrane over eye

Glossy Ibis with nictitating membrane over eye

Green Heron

Green Heron

Loggerhead Shrike head

Loggerhead Shrike

Bald Eagle eye

Bald Eagle

8 thoughts on “In the Blink of an Eye

  1. Normal you would not like it on a photo that birds close this ‘third eye lid’. In this case it is different. I think a lot of predators have this eye lid too. Cats use it when they attact (like owls ..). Do you know if they can still see when this lid is closed.. to keep an eye on what happens around them..???

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