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.
Parrots have thick tongues, so they don't need lips to approximate human sounds. The tongue's thickness, and where a parrot positions it in his mouth, allows him to imitate human speech. When air passes through the syrinx, the parrot moves his tongue to produce sound in his throat and mouth.
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.