I was recently on a trip in Peru and had the opportunity to view some truly beautiful birds. This is actually the farthest trip I have gone on to do any bird watching. One thing I did observe in many of the species is the beautiful colors of their eyes.
In some ways birds eyes are similar to human eyes as far as the basic structure. However, in proportion to the head the eyes make up a larger proportion. For humans, the eyes make up about 1 percent of the head. But for birds the eyes make up about 15 percent of head.
Typically, birdsí eyes are capable of little movement. So, they must move their head to change their field of vision. Much more so than humans would have to do. Their eyes are actually set further to the sides in their head, giving them a greater overall view but limiting their binocular vision which is the view in which both eyes can see an object.
The obvious exception to this are birds of prey, or raptors. We all know that if you walk past an owl it will turn its head all the way around. While they are capable of this, they cannot move their eyes in their heads at all.
There are two sorts of light receptors in the birds eye: Cones and rods. Cones help with vision during the day by increasing detail and accuracy, while Rods help with night vision by increasing sensitivity. There can be as many as 150 connected to only 1 nerve.
On the other hand, with cones, are usually only 1 or 2 per cell. Cones help to distinguish between different colors based on the different pigments they come in. They also help filter the light, or sort colors if you will. This is especially important to birds who see a similar color when flying. So, for example, seabirds whose vision is mostly blue water need to discern small object floating near the surface. The have red filters or pigments which cut out much of the blue light reflected up from the water.
Some other interesting bird facts?
Birds have 3 eyelids
Birds have 5 different pigments in their eyes while humans only have 3. This allows birds to see a great number of shades of colors than humans.