Nictitating membrane

posted in: Morphology-Develop. | 4

In April 2006 Johnny Wee spotted a White-throated Kingfisher (Halcyon smyrnensis) perching on a branch of a tree, eying a lizard on the ground nearby. He managed to take a few images with his digital camera as the bird launched at the prey. Back at his computer, he processed the images and found a number of them had birds whose eyes were white. Thinking that these were photographic artifacts, he erased them all.

In July 2006 Johnny observed a Pied Fantail (Rhipidura javanica) eying an insect. While intently concentrating on the prey, its eyes turned white and its tail feathers fanned out. This time he did not erase his white-eyed bird images but kept them as comparisons. The eyes returned to normal after feeding.

Two different observations on two different species of birds, both with eyes turning white just before the birds lunged on their preys must mean something.

Birds have three eyelids – one upper, one lower and a nictitating membrane. The third is between the two other eyelids and the cornea and moves sideways. It is used in cleaning and protecting the eye.

It is believed that birds cover their eyes with the nictitating membrane when under water. This has been disputed by some, as the membrane, being translucent and not transparent, would obscure the sight of the bird in its search for food. Others question the necessity of covering the eyes in water, based on our experience of seeing under water.

The nictitating membrane is also believed to comes in useful during flying. The bird cannot afford to close its eyelids often when in the air. Loss of vision, even momentary, caused by closed eyelids can throw the bird off balance.

Ornithologist Geoffrey Davison believes that the whiteness of the eye in the image is due to the nictitating membrane coming across the eye just at the moment the image was taken. This may or may not be related to the bird’s intended movement.

Birders-photographers, please keep a look out for this phenomenon in your images.

Latest: My copy of Handbook of Bird Ornithology (2nd ed.) (2004) by S. Podulka, R.W. Rohrbaugh, Jr. & R. Bonney (eds.), New York: Cornell Lab of Ornithology, arrived today. On page 1.7 it is said that “In raptors and other predatory birds, the nictitating membrane protects the eyes as the bird pursues prey through heavy cover, such as a blackberry thicket.”

Input by YC and Geoffrey Davison, images of Pied Fantail by Johnny Wee.

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4 Responses

  1. yes it is true the eyelid is for protecting it’s eye. I have taken lots of images of the Stork billed Kingfisher closing its eye lid when its in the water to protect it.

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  2. […] Choo Teik Ju’s sent in an image of the Common Kingfisher (Alcedo atthis) bashing a small fish it just caught against the branch it is perching on (left). Although a small fish, yet it has to be vigorously bashed before swallowing. As the kingfisher is bashing the fish, it is noted that the nictitating membrane covers the eye as a form of protection against flying debris. Kingfishers also does that just as it zoom in on a prey in the undergrowth. Check out more about the nictitating membrane HERE. […]

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  3. […] have three eyelids – one upper, one lower and a third, the nictitating membrane. This membrane is between the two other eyelids and the cornea and moves sideways. It is used to […]

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  4. […] and, when it shook off the water, had the nictitating membrane Stork-billed Kingfisher – a bad dayLINK drawn up to prevent injury (giving an odd look, above, […]

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