The musicality of birdsongs was popular with French classical composers of the late 19th and 20th centuries. Paul Dukas (of Sorceror's Apprentice fame) used to encourage his students to listen to the birds. One of his students, french composer Olivier Messiaen, transcribed the songs and worked them into quite a few of his works, including Le Réveil des Oiseaux and Catalogue d'oiseaux.

There's also a bit of birdsong in Beethoven's Sixth Symphony -- cuckoos, in particular.