[obol] Re: Nictating membrane?
- From: Dan Gleason <dan-gleason@xxxxxxxxxxx>
- To: canyoneagle@xxxxxxxxxxx
- Date: Sun, 6 Jul 2014 15:49:30 -0700
I believe that you are correct. This membrane sweeps quickly across the surface
of the eye, often so fast that we are not aware of it. However, cameras take a
small fraction of time and often, you will see this membrane in your photos
when you did not notice it while taking the photo.
The nictitating membrane has long been known about and even mentioned by
Aristotle. One of the first good descriptions was by Frederick II who wrote a
book on falconry and talked about this as something to clean the surface of the
eye. It does help clean the eye’s surface and as you noted below, it also
serves to protect the eye. Kingfishers close the eye with this membrane just
before entering the water and you will often see it clearly on Dippers as they
emerge from the water. In woodpeckers this membrane also helps hold the eye in
place when the woodpecker strikes a tree. The eyes of birds are very large in
relation to the head and the force of the strike could pop the eyes from the
socket if this membrane did not act as a retainer. Black-billed Magpies have an
orange spot on their nictitating membrane. Rather than fight, males assert
dominance by facing each other and tilt their heads back while flashing this
orange spot. Usually, the eye looking at the other male is the only one flashed
while the eye on the other side of the head usually remains open.
Dan Gleason
---------------
dan-gleason@xxxxxxxxxxx
• Co-owner, Wild Birds Unlimited of Eugene
• Author of "Birds! From the Inside Out" and "Looking for Yellowheads"
• Instructor of Field Ornithology, University of Oregon
541-953-4726
On Jul 6, 2014, at 9:54 AM, L Markoff <canyoneagle@xxxxxxxxxxx> wrote:
> While on the coast last week I took a few photos of a Peregrine at Yaquina
> Head. When I downloaded the photos I noticed its eyes looked odd. I am
> guessing this is due to its nictating membrane being engaged. If not that,
> then can anyone tell me what is going on?
>
> Photos here:
>
> https://www.flickr.com/gp/canyoneagle/X0Df8n/
>
> And here is a tidbit I found on the topic of nictating membrane from The
> Peregrine Fund:
>
> For additional protection, raptor eyes are equipped with not one, not two,
> but three eyelids. Two of their eyelids are just like ours; they move up and
> down to close their eyes. The third eyelid is known as a nictitating
> membrane, and this is the eyelid they use to blink with. It is a thin,
> semi-transparent lid, which moves from side to side. Closing and opening it
> helps keep their eyes moist and clean. When closed, it also helps to protect
> the bird’s eyes but still allows some vision. Raptors might close their
> nictitating membrane when feeding their chicks, when making contact with
> their prey, when in a fast dive, or even during a heavy rainstorm. An osprey
> closes its nictitating membrane when diving into water after fish - just like
> we might put on a pair of water goggles before plunging in to a pool.
>
> Lori Markoff
> Eugene
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