pipixcan.

PIPIXCAN, Franklin’s Gull (Leucophaeus pipixcan) [FC: 43 Pipixcan] “It is white, like a dove; its head is adorned [black and white]. It is a sea-dweller, an ocean dweller. It is called pipixcan because when it is about to freeze, when the maize is about to be harvested, it comes here.” Martin del Campo identified this as Franklin’s Gull. In fact, this Nahuatl term has been borrowed as the specific epithet for the Latin name of this gull. The Franklin’s Gull is a common fall migrant, September to December, which fits the pattern described. A quite similar species, the Laughing Gull (Leucophaeus atricilla), distinguished as PIPITZ-TLI, might also visit the Valley of Mexico, nesting occasionally.
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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.