The bird's eye contains a nictitating membrane which is a translucent, semitransparent inner eyelid. It sweeps across the surface of the eye enabling the bird to blink without losing sight of or without blocking their view.
Birds also have two different tear glands. One type of tear gland is located along the lower eyelid while the other is located at the base of the nictitating membrane. The second tear gland lubricates the bird's eyes whenever the nictitating membrane blinks.