GO-EVERYWHERE GOGGLES

Goggles are great for protecting eyes. When people need eye protection, we can grab goggles, but birds have built-in, go-everywhere goggles called nictitating membranes. The animals have upper and lower eyelids that open and close vertically, but their nictitating membranes open and close horizontally. These membranes, a kind of third eyelid, are translucent so birds can still see when the membranes