How Many Eyelids Do Ducks Have?

If you have a domesticated duck in your life, it probably never occurred to you before to pay attention to the little guy's eyelids. If you closely look at them, though, you might notice something a little surprising -- they're equipped with three of the things.

  1. Three Eyelids

    • Ducks have eyelids directly above and below their eyes. That's not where it ends, however. They also have third eyelids situated on the inner edges of their eyes. These eyelids are clear and are not without purpose. They're similar in functionality to goggles, which aim to defend the eyes against outside substances such as water. Remember, ducks spend a lot of time swimming.

    Nictitating Membranes

    • Ducks' additional eyelids come with special names -- nictitating membranes. They're indeed eyelids, but not typical ones, as they're transparent. Not only do the membranes help keep ducks' eyes safe from water, they also help keep them safe from dirt, dust and other random things that might be in the air. Although the majority of domestic ducks can't fly effectively or at all, some can. In those cases, the nictitating membranes can be highly beneficial for eye defense, too. Nictitating membranes enable eyes to stay wet -- no blinking necessary at all. Blinking can be risky for lots of animals. Predators can get to them in that instant that their eyes are closed.

    Closing Their Eyes

    • When you shut your eyes, you probably see a whole lot of nothing. This isn't so when ducks shut their nictitating membranes. When they shut them, their vision remains as strong as it normally is.

    Other Animals and Nictitating Membranes

    • Convenient nictitating membranes definitely aren't duck exclusives, and far from that. Their fellow avians frequently have them, with raptors as just one example. Lots of reptiles also have them. Camels, bizarrely enough, have them. Camels' third eyelids actually serve as useful survival mechanisms for life in the tough deserts. They work to keep sand in the breeze from getting inside camels' eyes while allowing sufficient light for vision. You might even live with a couple of household members who have third eyelids. Just look over at your Yorkie and your domestic long-haired cat. Yes, cats and dogs have them.