tzonyayauhqui.

TZONYAYAUHQUI, Lesser Scaup (Aythya affinis) and/or Ring-necked Duck (Aythya collaris) [FC: 37 Tzoniaiauhquj] “It is named tzonyayauhqui because its head is very black, much like charcoal, reaching to its neck Its eyes are yellow; its neck, its breast very white; its back dark ashen. Its tail is quite small, also dark ashen; its belly black, [but two] white [feathers] are placed on both sides near its tail. Its feet are black and broad. It does not rear its young here; it just comes [and] goes. Many come. They eat what is in the water, [as well as] the sand from the rocks and water plants seeds.” Martin del Campo did not attempt to identify this duck. However, the description fits the Lesser Scaup quite well. The Lesser Scaup is common in winter throughout Mexico. The Ring-necked Duck (Aythya collaris) is another possibility (Friedmann et al.). See also 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); Herbert Friedmann, Ludlow Griscom, and Robert T. Moore. “Distributional check-list of the birds of Mexico, Part 1.” Pacific Coast Avifauna No. 29 (1950). 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); Friedmann, Herbert, Ludlow Griscom, and Robert T. Moore. 1950. “Distributional check-list of the birds of Mexico, Part 1.” Pacific Coast Avifauna, No. 29; 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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.

The Florentine Codex includes a painting of this bird in Book 11, folio 38v. This source, below, concurs with the translation of "lesser scaup," adding (in Spanish) pato boludo menor.
Available at Digital Florentine Codex/Códice Florentino Digital, edited by Kim N. Richter and Alicia Maria Houtrouw, "Book 11: Earthly Things", fol. 38v, Getty Research Institute, 2023. https://florentinecodex.getty.edu/en/book/11/folio/38v/images/0 Accessed 17 October 2025.