mixcoacuauhtli.

MIXCOHUA-CUĀUH-TLI, Ornate Hawk-Eagle (Spizaetus ornatus) [FC: 40 Mixcoaquauhtli] "... is dark; its face is adorned." [FC: 41 Mixcoaquauhtli]: “It is not very large; average in size, somewhat the same as the turkey hen living here. It is named mixcoaquauhtli because at the back of its head are its feathers, paired feathers forming its head pendant. It is white across the eyes, joined, touching the black; so is the face adorned. The bill is yellow, curved. All its feathers are somewhat black [trimmed with] yellow. Its legs are yellow. It lives everywhere and is also a bird of prey.” Martin del Campo identified this as the “Crab Hawk,” now considered conspecific with the Common Black Hawk (Buteogallus anthracinus), no doubt because that hawk is a widespread, moderately large, overall black hawk. However, this interpretation does not account for the details of the crest feathers and face pattern. I suspect the name more likely applies to the Ornate Hawk-Eagle, the only Central Mexican raptor with conspicuous head plumes. Other details do not fit so well, as this hawk-eagle is quite large and is not predominantly dark.
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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.