Bald Eagle’s Nictitating Membrane

Bald eagles, like other birds of prey have incredible eyesight. To keep their vision sharp, bald eagles clean their eyes with the help of an inner eyelid called nictitating membrane. Besides protection, the membrane keeps the eye moist and clean of dust. It slides horizontally from left to right every three to four seconds. And, by being transparent, the eagle never loses sight of the prey even when the membrane is drawn across the eye.

Compare the bald eagle eye in the photographs below with the eyelid on and off.

Compare the bald eagle inner eyelid

This bald eagle is a three year and a half old female named Pandora. The bird belongs to Stephen Bucciarelli from Predator Bird Services. We met Pandora during the Wings of Spring Festival in Rondeau Park. We estimate that during Stephen's inspiring 1-hour long presentation, Pandora blinked her inner eyelid approximately 1000 times.

It takes about five years for the Bald Eagle to reach maturity and to gain its distinctive white head and tail that everybody recognizes. For this reason, young bald eagles are easily confused with golden eagles, especially when observed from a distance. Learn the clues provided by our readers on how to correctly identify the young bald eagle from the golden eagle.

As an interesting fact, birds are not the only species that have a nictitating membrane. Reptiles, sharks, amphibians, and some mammals such as polar bears have it too.

Let's take a closer look at Pandora and see the nictitating membrane at 100% magnification. Note the blood veins traversing the eyelid in great numbers.

Bald Eagle Inner Eyelid Closeup - Nictitating Membrane

We hope to meet Pandora and Stephen again. Till then we wish them both good 'hunting'.

Examples of the Nictitating Membrane in Other Birds
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{ 4 comments… read them below or add one }

HD March 24, 2010 at 3:09 pm

Perfect timing! What was the shutter speed?

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Mike Lascut March 24, 2010 at 3:48 pm

Hi Hong, I don't have the metadata in front of me, but probably either 1/3000 or 1/4000 at 600mm/f4 . Plenty of light outside :)

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Chester January 25, 2011 at 6:32 pm

Hi Mike,super-impressive shots! I can't imagine the patience and care about subject required to take that one.I'm into different kind of photography, but I couldn't help but leave a comment here. Great work!Keep up the great photography work adding to the great content of your website

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Mike Lascut January 25, 2011 at 6:37 pm

Hi Chester,
Thanks very much for your kind words and taking the time to leave a comment.
All the best,
MikeL

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