pipitztli.

PIPITZ-TLI, Laughing Gull (Leucophaeus atricilla) [FC: 39 Pipitztli] “It also lives in the water. Its head is black; its eyes are also black; white [feathers] are set on the eyelids [so that these] appear to be its eyes. It is somewhat long-necked. The throat and breast are white. Down the back of its neck, on its back, its tail, wings, wing-tips, it is black. The tops of both wing-bends are white. Its legs are quite long, chili-red, slender…. Some migrate, some remain and rear their young here. Four are its eggs; only on the ground, on dried mud, on the plain, or somewhere on the top of a clod it lays its eggs; not on gras nor feathers.” This must be the Laughing Gull, as it is the only gull known to nest in Central Mexico (Howell & Webb). The descriptive details all fit nicely.
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); Steven N. G. Howell and Sophie Webb. A Guide to the Birds of Mexico and Northern Central America (Oxford University Press, Oxford, New York, Tokyo, 1995); 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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.