An eye half-closed

[AgingEyes]

I took a shot of a sandhill crane I ran into this morning. Then I noticed its eye:




So they blink? Guess they have transparent eyelids then.

[Loupey]

It's the nictitating membrane that a variety of animals, birds, sharks, etc. have.

I have problems with big eyed birds (hawks mostly) as I get a large number of images with the membrane fully extended over the eye making for a gross looking bird