Last evening while HK was sitting near the camera you saw some very close up views of his eyes. Birds have two eyelids, upper and lower. Birds active during daytime hours raise the lower lid when closing their eye, and nocturnal birds close the upper lid. But birds also have a translucent nictitating membrane, sometimes called a “third eyelid”. This membrane closes across the eye from front to back. HK has this membrane closed in these photos. What is it used for? It is used to moisten and clean the cornea, especially in flight. It is also drawn across the eye when there is a chance the eye might be scratched or damaged such as when capturing prey, flying through brush or feeding their young. More about an eagle’s eye in future blogs.
Posted by: rlukei | June 18, 2009