The music of birds

French composer Olivier Messiaen was fascinated by the sounds that birds make, and their vocal landscapes influenced his music. He often transcribed bird "song" for piano, even orchestra. Here's an example from his composition, "Little Sketches of Birds."
And check out this website, which includes a fine essay on his methods, has another musical example, and is illustrated throughout by the work of Audubon: http://www.lichtensteiger.de/messiaen_oiseaux.html

And make sure, after you listen to Messiaen's music, that you also listen to the extraordinary sounds of the Lyre bird,as presented by David Attenborough, here: http://www.youtube.com/watch?v=VjE0Kdfos4Y