Empidonax virescens (Vieillot, 1818)
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Basis for Listing
The Acadian flycatcher breeds in deciduous forests of the eastern United States and southern Canada. It occurs primarily in mature forests, often near small streams, and is considered area-sensitive because it is found only in relatively large habitat patches. In the northeastern United States, it is generally found in woodlands larger than 40 ha (100 ac.) in size (Peterjohn and Rice 1991; Brauning 1992). In Minnesota, the Acadian flycatcher has always been rare. It was first discovered breeding in Beaver Creek Valley State Park in Houston County in 1967, where it has occurred regularly ever since (Lesher 1968). Its presumed regular breeding range in the state includes far southeastern Minnesota, north to Wright County and as far west as Nicollet County. Outliers have been observed during the breeding season in Douglas, Stearns, Chisago, Lincoln, and Lyon counties, but it is unknown if this represents an actual range expansion or an anomaly. Because of the rarity of the Acadian flycatcher's preferred habitat of large blocks of mature deciduous forest, and its irregular breeding occurrence in Minnesota, it was listed as a special concern species in 1996.
Acadian flycatchers are one of several closely-related species which are so similar in appearance that they are extremely difficult to identify solely by sight. This species is a small, olive-green bird, with whitish underparts, yellowish belly, two buffy or whitish wingbars, and a yellowish eye ring. Acadian flycatchers are best distinguished from other flycatchers by their distinctive song, which is a loud "PEET-sah" or "TEE-chup" (Whitehead and Taylor 2002).
Acadian flycatchers prefer large tracts of mature, intact, closed-canopy deciduous forest on both their breeding and wintering grounds (Whitehead and Taylor 2002). They are usually found near streams (Mossman and Lange 1982) or wetland openings. In southeastern Minnesota and the Minnesota River valley, the species is typically found in steep-sided valleys, with clear, swiftly flowing streams, but they are also found in silver maple dominated floodplain forests. In the Twin Cities metropolitan area, suitable habitat for this species is also found in forested areas on varied terrain, near small wetland openings.
Biology / Life History
The Acadian flycatcher is a middle-distance migrant that breeds in the United States and winters in southern Central America and northern South America. It feeds exclusively on insects and other arthropods, such as spiders. The species hunts by quietly watching for prey from a perch, and then sallying forth to capture prey. The Acadian flycatcher is territorial during breeding and migration, and possibly even in winter. Male Acadian flycatchers return to breeding grounds about one week before females. They are a monogamous species, which pairs in the spring as females arrive (Whitehead and Taylor 2002). Females construct a disorganized nest, strung like a hammock in the fork of a small branch, 2-4 m (8-12 ft.) off the ground. It is composed of cankerworm or spider silk, bark strips, forest herbs and grasses, and other fine materials. The female lays three eggs, which are white with a few brown spots. The female incubates and broods chicks, but both parents contribute to feeding. The altricial young hatch in two weeks, and fledge two weeks later (Whitehead and Taylor 2002). Acadian flycatchers usually have one brood per breeding season.
Conservation / Management
This species appears particularly sensitive to forest fragmentation and stand size. Brown-headed cowbird brood parasitism and predation are two factors that can negatively affect Acadian flycatcher populations in fragmented forests (Whitehead and Taylor 2002). Studies in Illinois have shown a strong positive correlation between Acadian flycatcher abundance and forest size, with a decline in birds as stands become smaller and more fragmented. In Maryland, Acadian flycatcher abundance was highest in forests of >3,000 ha (7,413 ac.). Acadian flycatchers were rarely found within 30 m (98 ft.) of a forest edge in the Baraboo Hills, Wisconsin (Mossman and Lange 1982).
Conservation Efforts in Minnesota
The Minnesota Biological Survey breeding bird surveys have greatly increased knowledge of the distribution of Acadian flycatchers in the state. Singing males have been found in more than 16 counties. However, at most sites only one or two singing males have been documented. Further inventories, monitoring, and research on habitat characteristics are needed, particularly at sites with relatively large populations.