Hammond's Flycatcher is a common but poorly known migratory species that breeds in mature coniferous and mixed forests of western North America from New Mexico and Colorado to Alaska. It winters primarily in the highlands of Mexico and Central America in cool forested regions similar to those occupied on the breeding grounds. It is perhaps most renowned for being difficult to identify in the field, often being confused with the Dusky (E. oberholseri) and Gray (E. wrightii) flycatchers, whose habitats occasionally overlap those of Hammond's. Size and color differences among these species are subtle, and the songs and calls, especially of Hammond's and Dusky, are similar enough to make field identification difficult for the casual observer.
Hammond's Flycatcher is primarily an aerial forager, capturing most of its insect diet on the wing. On occasion it may forage extensively from leaf surfaces or from the ground. Foraging tactics vary with stage of the breeding cycle, as foraging from leaf surfaces and from higher levels within the canopy are more common early in the breeding season. Although a few detailed studies of its foraging behavior, migratory routes, and taxonomic relationships have been conducted, detailed information on its basic natural history is lacking. Because this species frequently nests high in conifers, saddling its nest on a horizontal limb well away from the main trunk, its nests are difficult to locate and regular checks of the nest contents are arduous. Based on small sample sizes, Hammond's lays a clutch of 3 to 4 eggs in early Jun, incubates them for about 15 d, and fledges its young about 16 to 18 d after they hatch, usually in mid-Jul. Both members of the pair feed nestlings and fledglings, but only the female incubates the eggs and broods the young.
Logging may adversely affect this species, which prefers mature and old-growth coniferous forests, generally stands of more than 10 hectares and a minimum age of 80 to 90 years. Breeding Bird Survey (BBS) data show an increasing but nonsignificant trend for both the U.S. and the continent during the period 1966–1991.