From Alex Ross, "The Rest is Noise: Listening to the Twentieth Century" (New York: FSG, 2007)
The "swan hymn" -- the second movement of the fifth symphony came from this:
"The composer...recorded it in his notebook next to a description of sixteen swans flying in formation over his Ainola home.
'One of my greatest experiences!...Lord God that beauty! They circled over me for a long time. Disappeared into the solar haze like a gleaming, silver, ribbon..That this should have happened to me, who have so long been the outsider.'
The swans reapppeared three days later:
'The swans are always in my thoughts and give splendor to my life. It's strange to learn that nothing in the wole world affects me -- nothing in art, literature, or music -- in the same way as do these swans and cranes and wild geese. Their voices and being.'