Their calls have evolved over millions of years

This means that basic information about the zebra finch song must be stored somewhere in its genome,imprinted there by millions of years of evolution.At first, this might seem odd,as we usually think of genetic code as a source of biochemical or physical traits,not something like a behavior or action.But the two aren’t fundamentally different;we can connect genomes to behavior through brain circuitry. The connection is noisy and quite complex.