The Acadian Flycatcher’s unobtrusive behavior belies its explosive peet-sah territorial song, which is frequently heard in breeding habitats. A widely distributed breeder in forested landscapes of the eastern United States, the Acadian Flycatcher has the longest primaries and largest bill of the 5 eastern Empidonax flycatchers (1). It is generally a species of mature deciduous forest in its core range, but readily nests in conifers in appropriate habitats in the Southeast, and especially in eastern hemlock (Tsuga canadensis) in the northeastern portion of its breeding range (2, 3, 4, 5, 6). The species formerly nested north to southern New England, but became absent there in the early 1900s, perhaps due to extensive deforestation in the early 20th century. Reestablishment in the northeastern states began in the mid 1900s, where it appears to have undergone further expansion since the late 1970s.
It is usually associated with water and found in bottomland forests along small streams and in swamps. Nests are shallow and sometimes so flimsy that the eggs may be visible from below (7, 8). This is the only species of North American Empidonax whose nest is often adorned with 'nest tails', strands composed largely of catkins and spider silk that dangle below the nest (9). The hammock-like nests are built in a fork near the end of a branch, generally 3–9 meters above the ground. The female does all of the nest building, incubating and brooding, and both sexes feed nestlings. Although the proportion of females that double brood varies, second broods are relatively common, and the highest proportions have been reported from Virginia and Pennsylvania. Brood parasitism also varies, but is generally lower than for other forest-nesting species except in highly fragmented forests (10).
Relatively little information is available on the specific diet of this species. It forages, primarily by gleaning and sally-hovering on insects and other arthropods, particularly on the undersides of leaves. Occasionally, aerial hawking and ground feeding behaviors are used to catch prey. Small amounts of fruit are sometimes consumed.
Over the last 50 years, North American Breeding Bird Survey (BBS) data indicate that the rangewide population of the Acadian Flycatcher has been relatively stable, although declines have occurred in western and central portions of the breeding range (11). BBS data from 2011–2015 show highest counts (10–30/route) in coastal North Carolina, central West Virginia, southern Ohio, southern Indiana, western Tennessee, and central Mississippi (11). Although generally common and widely distributed, it has been accorded a relatively high priority for management (12). Major threats include habitat degradation and forest fragmentation.
Much of what is known about the Acadian Flycatcher derives from classic studies of natural history and breeding biology in Michigan (8, 13). In recent years, new information on breeding biology and the environmental factors influencing reproductive success has been obtained from studies across the range, especially Indiana, Illinois, Missouri, Pennsylvania, Ohio, and the Mississippi Valley (e.g., 14, 15, 16, 17, 3, 4, 5, 18, 6, 19).