European Green Woodpecker DSC_1351
European Green Woodpecker / picus viridis. Lincolnshire. 24/06/16.
NICTITATING ! (What a great word I've learnt today).
It was thrilling to spend time with a pair of Green Woodpeckers as they fed along the top of a grassy bank beside a ditch.
GW's have a nictitating membrane in each eye which is translucent.
It is sometimes referred to as a 'third eyelid' or 'haw' and moves horizontally across the eyeball. They can tighten their nictitating membranes a millisecond prior to their beak impacting the trunk or branch of a tree. This action prevents any shaking-induced retinal injury.
Of course, they use it often, in all sorts of situations in their daily lives. I was delighted to catch the male using his as he fed on the ground. The action moistens the eyeballs whilst still maintaining vision.
Viewed large you can see the membrane has been drawn across from the corner of the eye (left) towards the back of the eye (right). The small area of eyeball which has not been covered, appears very white by contrast. At the same time, the upper eyelid has been partially lowered over the membrane.
Fascinating...hope you think so too!
European Green Woodpecker DSC_1351
European Green Woodpecker / picus viridis. Lincolnshire. 24/06/16.
NICTITATING ! (What a great word I've learnt today).
It was thrilling to spend time with a pair of Green Woodpeckers as they fed along the top of a grassy bank beside a ditch.
GW's have a nictitating membrane in each eye which is translucent.
It is sometimes referred to as a 'third eyelid' or 'haw' and moves horizontally across the eyeball. They can tighten their nictitating membranes a millisecond prior to their beak impacting the trunk or branch of a tree. This action prevents any shaking-induced retinal injury.
Of course, they use it often, in all sorts of situations in their daily lives. I was delighted to catch the male using his as he fed on the ground. The action moistens the eyeballs whilst still maintaining vision.
Viewed large you can see the membrane has been drawn across from the corner of the eye (left) towards the back of the eye (right). The small area of eyeball which has not been covered, appears very white by contrast. At the same time, the upper eyelid has been partially lowered over the membrane.
Fascinating...hope you think so too!