cuacoztli.

CUA-COZ-TLI, Canvasback (Aythya valisineria) [FC: 35 Quacoztli] “It is a duck, called quacoztli because its head and its neck are tawny to its shoulder. It is large…. Its eyes are chili-red; its breast white; its back ashen, a little yellow…. Of its down are made capes. It does not rear its young here, but also migrates.” I agree with Martin del Campo that this is the Canvasback. The description might apply as well to the similar Redhead (Aythya americana). Both are common in winter in the Valley of Mexico. The Redhead may nest here occasionally. See CANAUH-TLI duck.
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 11 – Earthly Things, no. 14, Part XII, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1963); Rafael Martín del Campo, “Ensayo de interpretación del Libro Undecimo de la Historia General de las Cosas de Nueva España de Fray Bernardino de Sahagún – 11 Las Aves (1),” Anales del Instituto de Biología Tomo XI, Núm. 1 (México, D.F., 1940); and, with quotation selections, synthesis, and analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.