As for most neotropical birds of prey, details on the nidification of the rare, but widespread Black Solitary Eagle (Harpyhaliaetus solitarius) are fragmentary. Brown and Amadon (Eagles, hawks and falcons of the world, McGraw-Hill, New York, 1968) provided a summary of the information available to them on the nesting of this species in Sonora, Mexico. This note clarifies and adds to their account. The senior author and the late W. J. Sheffler spent the spring and summer of 1947 engaged in field work in the vicinity of Ranch0 Guirocoba, a well-known collection locality in southwestern Sonora. In early June, while visiting the small village of Mirasol (27”lO’ N; 108”6OW), about 25 km NE of Ranch0 Guirocoba, a local hunter described to them the nest of a very large bird of prey which he had found approximately 8 km E of Mirasol. On 7 June, the senior author, accompanied by the hunter and several other local residents, traveled to the nest site on horseback. Because of an untimely illness, Mr. Sheffler was forced to remain in Mirasol. The site was reached after a half day’ s ride through exceedingly rough terrain in the foothills of the Sierra Madre Occidental to a region known locally as the “Tecorawi” Mountains. The nest proved to be a huge affair located near the top of a Mexican yellow pine (Pinus ponderosa) growing on a steep slope overlooking a densely wooded canyon (fig. 1). As the party neared the nest tree, a large black bird flew from the vicinity of the nest and was immediately shot by a member of the party, Rodney Montgomery. Upon examination, it proved to be an adult female Black Solitary Eagle. This specimen and an adult male, which was obtained by Sheffler and A. J. van Rossem in the following year at a locality about 18 km N of the nest site, provided the basis for the description of a new race, Harpyhaliaetus solitarius sheffleri (van Rossem, Proc. Biol. Sot. Wash. 61:67-68, 1948). The