The American White Ibis demonstrating his third eyelid, also known as a nictitating membrane. This translucent "eyelid" offers protection and also moistens the eye while still maintaining vision. Rare in primates, it's found in fish, reptiles, amphibians, birds and some mammals. Isn't nature fascinating?
400mm | f/5.6 | ISO 160 | 1/1600 sec