The Peacock and the Araponga

David Hurwitz writes about Sibelius's Swanwhite (1908):

"The opening movement, 'The Peacock,' has castanets imaginatively imitating the bird's clacking beak. Even more interesting is the pedal point on the note E that runs through the entire piece in oboes, clarinets, and harp. Brazilian composer Heitor Villa-Lobos coincidentally used exactly the same technique in the second movement of his Bachianas Brasileiras No. 4 (1936), where the obstinately repeated pitch also represents a stylized birdcall."

from Sibelius Orchestral Works: An Owner's Manual, p. 181. Villa-Lobos's bird is the Araponga, and the repeated note in BB#4 is a beautiful effect in the orchestral adaptation, but especially in the original piano version. The bird-call is is in si bémol: B flat.