The music by Olivier Messiaen is a combination of devout catholicism, extravagant imagination and love for nature. Initially, he made a name for himself by composing large-scale cycles and verbose titles. At several occasions, Messiaen explicated his intentions, which often included theology, symbology, and extensive considerations of colour, church modes and rhythm. Perhaps ironically, this colour composer was able to leave his mark on the less colourful avant-garde of the 1950s as well. With his 'Mode de valeurs et d'intensités', part 4 of his Quatre études de rythme, pointed the way for his students Stockhausen and Boulez, who developed serialism further. Messiaen's own development is characterised by the integration of birg song, which he recorded in the wild with his sketchbook and tape recorder. The pinnacle of his work is his opera Saint François d'Assise. This colossol work is over four hours long. Its longest scene contains a giant bird choir, with bird species from Umbria (the home country of Saint François) to new Caledonia.