Monday, January 3, 2011

Downy Woodpecker 1

Last Sunday, Erika and I birded the River Bend Nature Center in Faribault, Minnesota. Returning home, I was surprised by this Downy Woodpecker's dull eye.  I enlarged the the photo below and discovered that I had captured the bird's nictitating membrane in action.
All birds have nictitating membranes, third eyelids that blink sideways across their eyes.  The membrane is transparent and moistens the cornea.  This Downy's nictitating membrane appears to be fairly opaque, which would be a pathological condition.  I researched the Internet and discovered that the membranes also protect birds' eyes much as do aviators' or divers' goggles.  Woodpeckers, indeed, have relatively thick nictitating membranes to protect their eyes from flying wood chips (Bay Nature Institute).  Wikipedia further claims "Woodpeckers tighten their nictitating membrane a millisecond prior to their beak impacting the trunk of a tree in order to prevent their eyes from leaving their sockets."

I was delighted that this woodpecker posed in front of a snow bank--thus, the white background.  Elsewhere in this blog (5 March 1010) I discussed identification tips for Downy Woodpeckers.

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