metzcanauhtli.

METZ-CANAUH-TLI, literally, “[crescent] moon duck,” Blue-winged Teal (Spatula discors) [FC: 35 Metzcanauhtli]: “For this reason it is called metzcanauhtli: on its face it is decorated with white feathers like the [crescent] moon…. It does not rear its young here; it also migrates” (FC 35). No question here, as the facial marking described is uniquely characteristic of the male of this species. 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); 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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.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 35v.
Available at Digital Florentine Codex/Códice Florentino Digital, edited by Kim N. Richter and Alicia Maria Houtrouw, "Book 11: Earthly Things", fol. 35v, Getty Research Institute, 2023. https://florentinecodex.getty.edu/en/book/11/folio/35v/images/0 Accessed 17 October 2025.

the blue-winged teal (a bird)
Henry M. Reeves, "Once Upon a Time in American Ornithology," The Wilson Journal of Ornithology 119:2 (June 2007), 317.