Asked by: Florina Wostheinrich
Asked in category: medical health, eye and vision conditions
Last Updated: 30th Nov 2022

Is there a third eyelid for birds?

Birds have both upper and lower eyelids. They can be closed up to protect their eyes from drying out. They have an additional or third eyelid, the 'nictitating Membrane'. This helps to keep their eyes clean and removes any dust or other particles that may get in them.



So, why not have a third eyelid?

It is actually the remnant of an eyelid. It's called a vestigial in humans. This means that it doesn't serve its original purpose. You can find many other vestigial structures within the human body that quietly ride along with one of our ancestor species.

What animals also have a third eyelid? Full nictitating membranes are found in some mammals such as cats, dogs, polar bears and seals. It is often called the third eyelid, or haw. In scientific terminology, it can be called the plica semilunaris or membrana-nictitans or palpebra.

Are there two eyelids in birds?

Other birds, including raptors, have three eyelids. The two eyelids that they have are similar to ours. They move up and down to open their eyes. The true eyes are used by most avian species for sleeping. The upper eyelid of owls closes automatically when the bird blinks.

Are all birds equipped with a Nictitating Membrane?

Nearly all vertebrates have a nictitating membrane, which is found in fish, amphibians and reptiles, as well as mammals. They are only a vestigial structure in humans and other primates.