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"
Bird vocalization
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs (relatively complex vocalizations) are distinguished by function from calls (relatively simple vocalizations).
Definition.
The distinction between songs and calls is based upon complexity, length, and context. Songs are longer and more complex and are associated with courtship and mating, while calls tend to serve such functions as alarms or
enough protein for the bird, especially during breeding season and the juvenile's fledging period. Therefore, the hummingbird also feeds on arthropods, such as flies and spiders.
Behaviour Vocalization.
Although not a song-call, hummingbirds can often be distinguished by their buzzing sound made from rapid wing-flapping. Like most birds, the sapphire-throated hummingbirds has many calls, but their most common song is a high-pitched rattle sounding like "wi-didididididididididi".
Conservation.
The sapphire-throated hummingbird