Water Bird Eyes
By Dave Hanks
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)
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