An Unusual Aberrant Colored Keel-billed Toucan (Ramphastos sulfuratus, Ramphastidae) in Northern Costa Rica

Abstract Although plumage color aberrations are common in birds, they often are difficult or even impossible to properly identify in the field. Even though some of these aberrations are common, including progressive greying, leucism, and albinism, there is confusion among the mechanisms responsible for each of the color aberrations. Other color abnormalities, such as dilution and ino, are found or reported less frequently. The Keel-billed Toucan (Ramphastos sulfuratus; Piciformes: Ramphastidae) is predominantly black, red under the tail coverts, and the feathers above the tail that are white colored. It has a yellow bib covering the throat and chest with a red band countering it, and the skin of the face is chartreuse. The Keel-billed Toucan is most notable for its massive, multicolored bill that makes up to a third of its length. Here we report a genetic-based melanin deficiency producing an unusual coloration in the Keel-billed Toucan. An individual observed at Pital, San Carlos, in the lowlands of northern Costa Rica in October, 2020 lacked melanin, but retained carotenoids. As most parts of the plumage normally have both melanin and carotenoids, the yellow becomes visible where the black is now absent, such as the ventral feathers. We discuss possible explanations for this unusual coloration.