yollotototl.

YOLLO-TŌTŌ-TL, literally, “heart bird,” Rose-throated Becard (Pachyramphus aglaiae) [FC: 25 Yollotototl] “It lives there in [the province of] Teotlixco, toward the southern sea. It is quite small, the same as a quail. As for its being called yollotototl, the people there say thus: that when we die, our hearts turn into [these birds]. And when it speaks, when it sings, it makes its voice pleading; it indeed gladdens one’s heart, it consoles one. [On] its head, on its breast, on its back it is rather ashen, rather yellow. Its tail is black, only at the tips of the feathers, white [and black] are mixed. The wing-tips are white.” Martin del Campo identified this bird as the Rose-breasted Grosbeak (Pheucticus ludovicianus). He inferred this from the conspicuous red breast mark of this grosbeak. However, the Rose-breasted Grosbeak is a winter visitor to Mexico and thus not likely to be heard singing. I suspect that the bird in question may be the Rose-throated Becard, though the description of the wings and tail might favor instead the Gray-collared Becard (Pachyramphus major). Both sing plaintive songs (Howell & Webb).
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); 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analysis here also appearing in E. S. Hunn, "The Aztec Fascination with Birds: Deciphering Sixteenth-Century Sources," unpublished manuscript, 2022, cited here with permission.