The story
Not certain. From a local South American (perhaps specifically Chilean) name, which probably entered English via Spanish; perhaps related to Tupi casaroba, saroba.
Etymology from Wiktionary, CC BY-SA 4.0.
coscoroba
Today it means: An anatid bird, Coscoroba coscoroba, of the monotypic genus Coscoroba and the only swan not belonging to Cygnus. Full definition →