The Sulphur-bellied Flycatcher is a boldly patterned Tyrannid breeding from southeastern Arizona and northeastern Mexico south to Costa Rica and wintering in western Amazonia of South America. The presence of this species in the United States was first documented when H. W. Henshaw collected a family group on 24 August 1874 in the Huachuca Mountains, Arizona (Henshaw 1875c). Twenty years later, R. D. Lusk discovered and was the first to describe the nest and eggs of this bird, also in this region (see Bendire 1895; U.S. National Museum B27276). Today, the distribution of the Sulphur-bellied Flycatcher north of Mexico remains restricted, for the most part, to mountain ranges in southeast Arizona, where it is found in riparian can-yons in association with sycamores (Platanus sp.; for nest tree) and walnuts (Juglans sp.; for nest material). It is "one of the latest tree-nesting birds of the region, as it usually awaits the coming of the summer wet season" (Brandt 1951: 662).
This species was formally described by P. L. Sclater in 1859. Sclater was reporting on the collections of Auguste Sallé taken in southern Mexico and noticed the "new" species. This new form was present also among additional comparative material in collections of Matteo Botteri from southern Mexico, of Mr. Skinner from Guatemala, and of Prince Charles Lucien Bonaparte (who had named the species but provided no diagnosis). The type specimen from Sallé's collection was identified originally as Tyrannus audax (= Streaked Flycatcher, Myiodynastes maculatus).
The type locality was later restricted to Orizaba, Veracruz, Mexico, by P. Brodkorb (Brodkorb 1943a).
There is little published material about this species. Many references to Sulphur-bellied Flycatcher document only its presence at specific locations or offer anecdotal comments about the species. The only sources of hard data and information on breeding biology seem to be Skutch 1960a and Ligon 1971b . Skutch's work in Costa Rica also served as source for the species account in Bent 1942b; Ligon's observa-tions were made in Arizona. Both reports are based on observations of fewer than 10 nests.