During puberty: After infancy, the tween and teen years are the period of most rapid change. For girls, the growth spurt begins between 10 and 11 and lasts until around 15; for boys, it starts about two years later and lasts until age 17 or so. Girls typically stop growing about three years after they've had their first period, but boys continue to grow throughout their teens.
The Syrinx. Humans have a larynx, and parrots have a syrinx, located between the voice box and the bronchial tubes. The syrinx branches out in two directions, with each branch opening into a bronchus. Air from a parrot's lungs passes through the syrinx, and the parrot is able to use all of the air to produce sound.
All those bird sounds you hear are definitely forms of communication. Most birds tend to communicate vocally, although some are much more vocal than others. One of the most common forms of bird communication is a call note. In small birds, call notes may sound like chirps. In larger birds, call notes may sound like squawks. Each species of bird uses a variety of call notes to communicate different messages. For example, one common message birds convey via call notes is to alert other birds to the presence of potential danger.