YOHUAL-TLOH-TLI, literally “nocturnal falcon, perhaps Bat Falcon (Falco rufigularis) [FC: 45 Iooaltlhotli]: “It is the same as a falcon . It is named youaltlotli because it sees in the dark; it can hunt, it can strike its prey.” Martin del Campo suggested either the Swallow-tailed Kite (Elanoides forficatus) or the Lesser Nighthawk (Chordeiles acutipennis). Neither is likely. The nighthawk is insectivorous, thus quite unlike falcons, and the kite is not known to hunt at night. The Bat Falcon, as its name suggests, preys on bats, which fly at dusk and dawn, so the Bat Falcon must hunt as darkness falls.
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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.