Birds do not have a larynx like we do. Instead they have an organ called a syrinx. The syrinx is located much deeper in the bird's body than our larynx is and for many years scientists had little idea how birds actually made sound. Even today there is a lot we do not know. However, by dint of making birds do lots of unnatural things, like sing with fibre-optic scopes down their throats, sing in a helium oxygen atmosphere or sing with their beaks held open, while watching them with infra-red and x-ray cameras scientists have learned a little about how this amazing instrument works.

A bird's syrinx is a double instrument that sits deep in a bird's chest at the point where the trachea divides into two bronchi. A part of it rests in each bronchi and each of these halves is capable of making sound. This means that a bird can sing two different notes at the same time, or even sing a duet with itself.

Some birds such as thrushes do exactly this, they are even capable of singing a rising note with one side and a falling note with the other. Other birds use their dual vocal chords in different ways such as using one side for low notes and the other for high ones. Cardinals can switch from one side to the other in mid-note while canaries breathe through one side and sing with the other. Cowbirds sing very rapid notes one alternately from each side. It is this sort of ability that allows some birds to sing as many as 30 separate notes per second.

Imitating human speech is a difficult trick and parrots and their smaller kin, the budgies, use different techniques. Parrots have thick tongues like humans, a novelty among birds, which has the side effect of allowing them to form the sounds of words in a manner similar to us. That means that they emit a preliminary sound from their syrinx and then modify it using the mouth, throat and tongue. Budgies, however, are too small to do things like this. So they use their syrinx to create a 2-3 Kilohertz carrier frequency then add a second vibration to it. This is a well-known scientific system called frequency modulation and is the principle behind AM radio, however, how budgies actually do it is still a mystery so do not worry if you haven't understood this section too well.

Information on this page was contributed by EarthLife.

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