The story
From the misspelling "roulroul" in George Robert Gray's 1844 publication List of the Specimens of Birds in the Collection of the British Museum, from a misinterpretation of "Le Rouloul de Malacca" as an instance of reduplication in Giovanni Antonio Scopoli's Deliciae florae et faunae Insubricae, seu novae, aut minus cognitae species plantarum et animalium quas in Insubria Austriaca, tam spontaneas quam exoticas vidit, descripsit, from "Rouloul de Malacca" (plate 100) and its description (pages 174 and 175) in Pierre Sonnerat's 1872 Voyage aux Indes Orientales et a la Chine, fait par ordre du roi, depuis 1774 jusqu'en 1781, from the Malayic onomatopoeic rendition of one of the bird's calls.
Etymology from Wiktionary, CC BY-SA 4.0.