Nictitating membrane

on 16th August 2006

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.

If you like this post please tap on the Like button at the left bottom of page. Any views and opinions expressed in this article are solely those of the authors/contributors, and are not endorsed by the Lee Kong Chian Natural History Museum (LKCNHM, NUS) or its affiliated institutions. Readers are encouraged to use their discretion before making any decisions or judgements based on the information presented.

YC Wee

Dr Wee played a significant role as a green advocate in Singapore through his extensive involvement in various organizations and committees: as Secretary and Chairman for the Malayan Nature Society (Singapore Branch), and with the Nature Society (Singapore) as founding President (1978-1995). He has also served in the Nature Reserve Board (1987-1989), Nature Reserves Committee (1990-1996), National Council on the Environment/Singapore Environment Council (1992-1996), Work-Group on Nature Conservation (1992) and Inter-Varsity Council on the Environment (1995-1997). He is Patron of the Singapore Gardening Society and was appointed Honorary Museum Associate of the Lee Kong Chian Natural History Museum (LKCNHM) in 2012. In 2005, Dr Wee started the Bird Ecology Study Group. With more than 6,000 entries, the website has become a valuable resource consulted by students, birdwatchers and researchers locally and internationally. The views and opinions expressed in this article are his own, and do not represent those of LKCNHM, the National University of Singapore or its affiliated institutions.

Other posts by YC Wee

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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