The plaintive, whistled call of the Dusky-capped Flycatcher is a common sound in oak and pine woodland in southeastern Arizona and southwestern New Mexico as pairs maintain contact within dense foliage. This call is heard throughout this taxon's extensive range, from southwestern United States to northwestern Argentina.
The Dusky-capped Flycatcher is a diverse taxon with 13 subspecies. It is unique within the genus Myiarchus for the variation among subspecies in crown coloration and for habitat preference, with nearly complete reproductive isolation between subspecies at some points in South America (Lanyon 1978). In other places, defining subspecies boundaries is difficult, and intergrades are common. The factor uniting these diverse subspecies is the similarity (to the human ear) of their vocalizations. Voice appears to be the criterion used by the members of the genus Myiarchus to distinguish themselves; plumage differences among the (at least) 22 species are slight (Lanyon 1963a).
Formerly known in the United States as Olivaceous Flycatcher, Dusky-capped Flycatcher was described in 1837 by 2 French explorer-naturalists, Alcide Dessalines d'Orbigny (1802–1854) and Andre de Lafresnaye (1783–1861), from a specimen taken in Bolivia probably by d'Orbigny (Rounds 1990, Am. Ornithol. Union American Ornithologists' Union 1998a).
Over the years, other taxa, including M. olivascens, M. lawrenceii, M. platyrhynchus, M. nigricapillus, M. brunneiceps, M. nigriceps, and M. atriceps, have been merged into this taxon, based primarily on vocal similarities and contrast in coloration between crown and back.
As with other members of its genus, the Dusky-capped Flycatcher is not a social bird and may maintain territories year-round. It is a secretive cavity-nester; few nests have been found. Some egg collectors took advantage of the ready adaptation of M. t. olivascens to nest boxes (Brandt 1951). Few researchers have exploited this behavior.
Much of our very limited knowledge of Dusky-capped Flycatcher comes from the work of W. E. Lanyon (Lanyon 1963a, Lanyon 1978, Lanyon 1985, Lanyon 1997), who studied vocalizations and defined subspecies limits, and A. F. Skutch (Skutch 1960b, Skutch 1977, Skutch 1981, Skutch 1987 Skutch 1997), who recorded most of what is known of its life history.