More about birds

The House Crow and the Sparrow perhaps are the most common and abundant birds. They have followed man everywhere and hence wherever we live, it is possible for us to find these birds.

Next in abundance come birds like Mynas and Bulbuls. These do not entirely depend on man, but are quick to profit by his presence and activities.

There are many other birds around us. Some examples are pigeons, owls, kites, parakeets, and cuckoos.

Let us get to know more about birds.

Bird Eyes

Birds have highly developed senses of sight and hearing. While taste is comparatively poor, smell is practically absent. Though they look small, the eye (the complete eye including the visible outside part called the cornea) of a bird is extremely large. In most birds, the eyes are actually larger than the brain. The eyeball of an ostrich has nearly the same diameter of a tennis ball. The eye of an eagle or a large owl can be as large as man's eye. Also most birds' eyes do not move in their sockets as our eyes do. Reflex movements of their necks usually replace the eye movements.

Birds rely heavily on its sense of vision to survive.

Because sight is so important to them, birds have highly developed eyes, even more so than humans in many aspects. A great peculiar feature of a bird's eye is its power to change focus. Many birds need to look and react instantaneously to far as well as near objects. Most birds thus have both telescopic vision (ability to see far off objects) and perfect near sight (ability to see very near objects). For example, a warbler constantly on the vigil can bring to focus a tiny insect an inch away from its beak. This ability is of great use in protecting as well as finding food.

Birds' eyes vary in size and position from species to species.

Most birds have rather flat eyeballs with large retina. Such eyes are excellent for scanning the landscape. Birds of prey have rounder or almost tubular eyes. This will not give them a very large field of view, but will permit them to pinpoint at target, even when very far off.

Monocular vision
The eyes of most birds are on the side of their heads. This placement allows them to be able to see the things on each side at the same time as well as in front of them. This type of vision is called monocular vision. Birds with eyes placed like this get a wide area of vision to be able to see danger as quickly as possible. However, with monocular vision, birds have a harder time judging distances and have worse depth perception.

Binocular vision
The vision that occurs when the field of vision from each eye overlaps is called binocular vision. Such birds have much sharper vision to the front and cannot match the wide-angle view that birds with eyes on the sides have. Owls, with wonderful binocular vision, make up for the lower field of vision by an amazing ability to turn their heads to face backwards. Humans also have binocular vision.

Birds with eyes set more to the sides of their head have forward binocular vision and also side vision. Here is an example of sparrow's eyes

Birds with eyes set far to the back of their head have little forward and greater backward binocular vision in addition to side vision. Here is an example of a duck's eyes.

With forwards facing eyes, owls have a wide range of binocular vision. Very important to catch live prey.

Hearing in Birds

The hearing system of birds is similar to that of man and depends upon the pressure of sound waves on eardrums; these pressures are in turn converted into electrical signals and sent to the brain where it is interpreted. The sound range that birds can hear enable them to filter off many of the environmental sounds in nature, such as wind and falling rain, and help them in discerning the calls of their own species.

The ability to determine the direction of incoming sounds depends upon the discrimination in the brain between the strength of the signals reaching the two ears. Because the ears of a bird are closer together than those of most mammals, they would normally be at a disadvantage in direction finding. But they compensate for this by having a much better appreciation of the time intervals between sound waves, and this is equivalent to a wider separation of the two ears. Directional location of sounds is particularly important to birds, which live in dense vegetation, where the caller is often never seen at all.