As we will discuss in chapter 2, some species of birds can only acquire their
song during a specific period of development. In this respect bird songs are similar
to human language, for which there is also a critical period for acquisition.
Although this is an important aspect of both bird song and human language,
birdcalls and songs are fundamentally different kinds of communicative systems.
The kinds of messages that birds can convey are limited, and messages are
stimulus controlled.