Nictitating eyelids

Birds have nictitating membranes that are also referred to as a third eyelid; they are fascinating structures that I knew little about until I found myself photographing them surprisingly often.

 

Wedge-tailed Eagle (Aquila audax) 1/1250, f/7.1, ISO 800

 

The eagle above is not using its nictitating membrane but sometimes an […]