The Eye of the Avian

The EYE of the AVIAN is upon you;

Bold and bright, regally shining –

An entrée into the soul of each creature.

To be close-up and personal is but a hope,

Because their extraordinary sight prevents it,

And the ornithological world

Will retain much of its mystery and richness!

Vision is the most important sense for birds; in fact it is superior to almost all other vertebrates. Good eye sight is essential for flight. A secondary eye lid (nictitating membrane) gives extra protection and aids vision in less than favorable atmospheric conditions. Bird eyes also have ciliary muscles that can change the shape of the lens for a greater advantage. Bird eyes are the largest, in relation to their size, when compared with other animals.

Migrating birds can spot unused nests, or sources of food, from aloft and descend to feed or bed down for the night. Predatory birds such as hawks, eagles, and vultures have vision powers that are 3 – 4 times sharper than ours. Vultures and hawks can spot rodents from heights of 10 – 15,000 feet, and then dive at over 100 mph and still keep their target in focus. Eagles have tremendous vision. They can spot a rabbit that is several miles away.

There is a saying: “When entering the forest, the deer will hear you, the bear will smell you, and the bird will see you.”

(Dave Hanks)

A Short-Eared Owl keeps me at a distance with his incredible vision

A Short-Eared Owl keeps me at a distance with his incredible vision

Water Bird Eyes

Vision is more important to a bird than all of its other senses combined. The avian eye is a complex organ. While similar to the eyes of most other animals, it is more sophisticated. Whether in the sky or under water, the necessity for sharp vision is definitely increased. Hearing comes second, while smell and taste are a distant third and fourth. Birds can see in detail up to two or three times further than humans can. That’s one reason it’s so difficult to approach close to ducks that are used to being hunted.

Since such a large number of water diving bird species (and many other birds that utilize dark surroundings) have red eyes, it would suggest that it is an adaptation for seeing in places where light is limited. One could hypothesize that it might be similar to using an ultra violet light source for nighttime vision. The red color probably comes from a highly concentrated quantity of blood vessels that are close to the surface.

The nictitating membrane (extra eyelid) acts like swimming goggles. While protecting the eye when under water, it is light permeable and allows unimpeded vision. Bird eyes contain extra cones and the increased color awareness gives them a definite visual advantage. Their color perception is much more acute and rich than ours.

Since most of these water birds are prey species, their eyes are on the sides and high on their head. This monocular vision gives them a 360 degree view, which is much wider than ours. However, their side vision is better than their overhead sight and to study an object, they must use only one eye at a time. The bird’s necks are not as flexible as ours and so they are constantly moving their heads this way and that. The jerky movements remind one of the late comedian Roger Dangerfield and the seemingly nervous actions of his comic routine.

The pictured Western Grebe is the most common grebe on our Snake River.

Red eye brilliantly aflame

Eyes: Windows to the Personality

When I do photography, I have always tried to focus on an eye. A bright, clear eye in a picture makes the photo come alive – without the eye the animal is incomplete. Eyes are also a body adaptation that furnishes a key to how a species lives and survives.

For instance, a predatory life style can be ascertained by noticing the forward looking, binocular vision eyes. The same can be concluded for prey species with their eyes more to the rear, or actually on the side of the head, which allows detection of something approaching from behind. Nighttime predators have enlarged eyes that have many rods in them. An owl’s eyes are so big that they make up a third of the head. Other feathered predators, such as eagles and hawks, usually have yellow eyes. The yellow is the result of an oil-like inner eye secretion that is yellow, and it acts the same way as a filter on a camera does – an adaptation for an animal that must deal with bright sunlight. The placement of the eye is positioned to give each beast an advantage – i.e. giraffes with eyes situated to look down toward the dangers from ground level; or eyes placed on top of the head – such as frogs, hippos, and alligators that live in water. Their bodies can remain submerged with only their eyes out of the water. The Crocodilians may appear like a floating log, but they are well aware of any surface activity. Some lizard’s eyes are not on the same level with each other, giving them a wide range of vision.

Many animals have two eyelids: the outer one that closes the eye to light and other invasions, and an inner nictitating membrane which allows some light in and therefore some vision while still giving partial protection to the eye ball. Snake eyes have no eyelid and that is probably one reason that they appear eerie. They deal with light by the construction of their pupil. Each species pupil is adapted to the habitat it lives in: round, where light is no problem; elliptical vertical, against light from the side; elliptical horizontal, where there is more over head light; and pupils punctuated in a line of tiny holes, is an adaptation against extremely bright conditions.

Yes, eyes really are the doorway to an organism’s being!

The American Alligator – An example of eye adaptation

The American Alligator – An example of eye adaptation

These Woods are Alive!

Climb to the top of a mountain,
or perhaps just a moderate hill.
Just look at all that’s around you,
but that’s not all, there’s more still.

In the valleys below you,
in the edge by that stream,
If one opens one’s eyes,
it will certainly seem –

That where you see two,
there must really be five.
Six becomes eleven.
These woods are alive!

What causes this awakening?
Opening your senses is the key.
To be out tasting nature
is a wonderful place to be!

(Dave Hanks ’07)