Principal English Translation:
Russet-naped Wood-Rail, a bird (see Hunn, attestations); the word might seem to have a Hispanized orthography (perhaps originally, popoca-calli, smoking house) but sources emphasize that popocales is the sound the bird makes, "po-po-kalli-kalli" (an onomatopoetic word)
Attestations from sources in English:
PŌPOCALES, Russet-naped Wood-Rail (Aramides albiventris) [FC: 25 Pôpocales] “Its home is in the forest. As for its being called popocales, it speaks so. Always in the twilights and a dawn, it says popocales. And it frequents the canyons; it lives there in [the province of] Toztlan [and] Catemaco. It eats fish. It is the size of a duck, only a little taller.” Martin del Campo suggests that this is some species of rail (Rallidae). The description fits the Russet-naped Wood-Rail.
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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.