I don't know about birds influencing the history of music....yet i think I've heard about Mussorgskij been influenced by their singing, Cage having them sing right on stage....but what i wanted to say - birds aren't exploited yet. There's much inspiration that can emerge out of their melodies. It is a strange approach to "music" as intuitive that the mankind, according to myself, didn't make use of it. But it's just another force of nature. Using bird sounds as a sketch to one's own music would be as valid and of the same quality as using any other source. Maybe even worse, because the art (maybe sorry for introducing my own point of view, i still think of this forum as a free forum for possibly clear debate) should be a revealing of one's own vocabulary using techniques learnt and experiences modulating those learnings. And that should create uniqueness.