KS 2: Composing bird songs allows children to explore essential elements of musical language. Ask them to experiment with some fundamental patterns on tuned instruments: trills (where two adjacent notes alternate very fast - good for xylophone technique), slower pairs of repeated notes like the cuckoo call, repetitions of the same single note, adjacent notes played simultaneously and repeated, slides up and down over a specific interval (glissando), and grace notes (where two notes are played almost - but not quite - at the same time). Primary pupils can make up a sequence using some of these ideas, create a graphic score and invent and describe a bird to sing it.
KS 3: Older children can experiment (like Messiaen) with using the different timbres of chosen instruments to play selected sections of the sequence and write a full score showing how it works. They might even use Messiaen's violin marking from his marvellous Quatuor - "comme un oiseau" - at the head of their score.