Another Postcard

As if posing for a postcard, this Great Egret stalked the hill on the northwest corner of the park, with the Golden Gate Bridge and the city of San Francisco as background.

Great Egret (Ardea alba)

At one point, the bird walked within just a few feet of me and my tripod, as if it were a chicken in a barnyard. At that point I could not resist snapping another head shot, followed up with a tight zoom on the bird’s eye. Egrets have upper and lower eyelids, although I’ve never seen them in operation. The Burrowing Owls, by contrast, have prominent eyelids and calibrate them to the available light and their level of alertness; they can even wink with one eye. Birds also have a tough, transparent inner membrane that slides sideways to cover the whole eye. That’s called a nictitating membrane, and it’s what allows eagles and other raptors to dive at 200 mph without injuring their eyes while still being able to see. Read about it here and here. In this photo, the nictitating membrane is not deployed. The egret may use the membrane momentarily when it strikes at a target.

Great Egret (Ardea alba)
Great Egret (Ardea alba) eye

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