The eleven species of North American Empidonax flycatchers are some of the most migratory birds in the United States and are also some of the toughest to identify. With songs, habitat, and range providing better identification cues than plumage, this group of subtle flycatchers stymies beginners across the nation and present continuing challenges even for expert birders. eBird data quality filters ensure that reports to eBird meet known distributional patterns, but given the ID challenges we are still very pleased with the accuracy of the occurrence map results for Acadian, Willow, Hammond’s, and Dusky flycatchers.
Acadian Flycatcher breeds in the southeastern United States, with the northern extension of its range barely reaching western Massachusetts. In southeastern swamps they like groves of American Holly while in the Appalachians they can be found in cool, wet hemlock ravines. It arrives rather late in spring, with northerly breeders not occupying territories until late May. As is often the case with southeastern breeding passerines, fall migration shows up as a gradual fade out rather than a pronounced southward passage. Fall birds linger in Gulf coast states to mid-October, so the timing of the STEM maps looks very good for this species.
As accurate as this map is with respect to range limits and timing, an obvious error appears in northern Minnesota in late summer and fall. Acadians practically never occur here. This area of sparse data presents some regular problems for these STEM maps and we are working to make the results from here. The eventual incorporation of Canadian data (which depends more on getting the landcover data from outside the US than in getting the bird data, since we have a large cadre of Canadian eBirders (thanks to partnerships with Bird Studies Canada) could help to better define the bird occurrence at the northern limits of the United States. Another apparent error is the late March flash of color on the Carolina coast, before bird arrive on the Gulf.