The Australian Emu (Dromaius novaehollandiae) has protective nictating membranes on its eyes. The membrane over each eye protects them from dust.

A nictating membrane is a transparent or translucent eyelid. The eyelid membrane not only protects the eye from dust, it also moistens the eye and cleans away any dust or dirt. This is because the emu lives in dry, dusty areas of Australia.

Nictating means blinking. The eye membrane is called a third eyelid, or a haw, or a plica semilunaris, or a membrana nictitans.