I can do pretty good impressions of birds. Do you know about that? 
Can you do both bird calls and bird songs?
Yes I think I do both. What is the difference though exactly?
In birding, songs are distinguished by function from calls.
That's pretty interesting. What kind of functions are we talking here?
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
John Lennon and McCartney wrote together or separately before they had a publishing deal. Talking about such early songs, McCartney said "We wrote a few that never got published, before we went with a publisher, and I say, it's really now they're in here [his memory]. They never got put down anywhere so there's really only my memory that can sort of remember them, you know. So it's something I want to do something with actually, 'cause they're pretty rough songs, but