I've heard the phrase bird vocalization before but I really don't know exactly what it means.
Its not a common theme but it refers to bird calls and bird songs
Made by the birds themselves correct"
Made by the bird themselves but I guess if a human could mimic it then it should count also. Its a bird sound that is melodious to human ears.
Ah okay, that's interesting. Especially how different birds have different calls and for different things too.
There is a difference between songs and calls as its based on its length and context and complexity.