Paul Griffiths comments that Messiaen was a more conscientious ornithologist than any previous composer, and a more musical observer of birdsong than any previous ornithologist. --- Wikipedia
Click to watch and hear about Birdsong in Messiaen (particularly with Peter Hill).
Click to read an excerpt from Rebecca Rischin, For the End of Time, about birdsong in general and in particular in Le Quatuor pour la fin du temps (begin on midpage 57).
The third movement of Le Quatuor: L'Abîme des oiseaux, Walter Boeykens, clarinet. [listen]
Click to read more about birdsong in Messiaen from French Music since Berlioz by Richard Langham Smith, beginning page 346.