How Do Birds Detect Danger?

I have often wondered, watching the little feathered friends in my yard, just how they detect danger from a distance in order to have time to escape before it gets to them. The more a person listens to the intricacies of a bird's songs and chatter you learn to differentiate between something that sounds like a bird singing from joy or happiness to something of an alarm tone to other birds.

Birds have an intricacy and depth to their communication. If you listen to any certain bird in your area, and you think you become accustom to the call it is generating, that same bird will generate a completely different call than the one you had been listening to all that time. You think to yourself what is this new message and what is the bird telling his or her comrades. Beyond a well developed eyesight, birds are dependant on their sense of hearing for survival. Take for example; a barn owl can hunt by sound alone, a woodpecker can hear insects under the bark of a tree. Pigeons are said to be able to detect infrasonic waves that come just prior to an earthquake.

Hearing helps birds detect and locate danger, food, water, and territory and shelter. Birds have a greater hearing range of sounds than humans do. Birds have what is called a "Syrinx" this organ unique to birds allows them the range of vocalizations they use. It is located just above the fork of the bronchial tubes and just below the trachea. The "Syrinx" could be related to a mammal's larynx in that it produces sound when air is forced through the trachea causing the membranes to vibrate. Unlike the larynx the syrinx is a lot more efficient using all the air passing through to create sound. A human by comparison only uses 2 percent of the air exhaled from their lungs.

Take those facts and combine them with a bird's hearing. Birds have ear canals that are protected by feathers called "Ruffs" called "ear coverts" or "auriculars". These feathers do not interfere with the sounds, but help funnel sound into the ear passages to the cochlea, the sound receptive organ. Owls for are one of the best examples of facial and head feathers help direct sound. The ear opening of birds is just below and behind the eyes. The "auriculars" funnel the sounds toward the eardrum, which is a thin membrane stretching across the ear canal. There a small bone called a "columella, is attached to the rear of the eardrum and transmits the vibrations through the middle ear to a second membrane across an opening, called the oval window, in the cochlea. The "cochlea" is the hearing organ. It is a fluid-filled chamber with hair like cells or "cilia". When some movement in the fluid is caused by vibration it causes the "cilia" to move, this in turn creates nerve impulses that are transmitted to the brain by the auditory nerve. Then the "round window", another membrane covered opening, protects the "cochlea" by allowing the pressure waves in fluid to dissipate through it.

There is also an inner ear compromising the semicircular canals, which in turn regulate orientation and balance much as they do in a human being. All of this to say that when you hear birds in the trees or on the ground making a high pitch sound, or maybe something you are not use to hearing a particular bird make, if you pay attention. You might learn that birds have a high degree of self awareness and preservation of themselves and their avian families from all types of potential predators including sadly, man.

Reference:
sound reception.(2007). In Encyclopedia Britannica. Retrieved December 2, 2007, from Encyclopedia Britannica Online: http://www.britannica.com/eb/article-64819