From Frederic Morton’s A Nervous Splendor: Vienna 1888/1889.
By then the word Mayerling had already begun to phosphoresce throughout the world. Abroad it tingled and thrilled. In Vienna it was like some hidden hell machine of which nothing was known except that it was made of gold. Now and then the city tried to shake off the giant riddle that undermined its boulevards. There erupted rumors of some rational solution. At one point word spread that Johann Pfeiffer, King of the Birds, had heard his parrots speak the truth of what had happened in Rudolf’s hunting lodge. A crowd formed at the Schottenring. The police borught the man and his black-craped cage to a precint house. But the birds just bithered and jabbered in panic, and their King lost his renowned humor. The bafflement continued.