Some types of birds, such as raptors, waterfowl, and warblers, appeal to both birdwatchers and sane people alike. Members of these avian families are fun to observe at least in part because they appear in a broad array of easily-discernible forms. Given a minute with a field guide, most individuals can separate different types of ducks or owls. But other cognate bird species are so alike in appearance that even experienced birders have trouble identifying them with confidence. For example, many birders find themselves frustrated by gulls, since they all look so much alike yet dissimilar. I also take little pleasure from picking out the individual species in a flock of peeps. But the toughest group of North American birds to identify in the field has to be the assorted Empidonax flycatchers.
All tyrant flycatchers in the genus Empidonax, called empids out of either affection or frustration, are suboscine songbirds with olive upperparts, pale throats and bellies, and whitish wing-bars and eye-rings. These active insectivores are usually pretty small, roughly 5.5 inches in length, give or take a half-inch. In size and plumage, which is generally variable due to due to molt, wear, and age, the various Empidonax species are virtually identical. Thus, to identify an empid confidently without resorting to an autopsy, one must rely on voice, behavior, habitat, or range. The bad news is that habitat and range often overlaps for multiple species, especially during migration. Even worse, empids have an uncanny knack for keeping their mouths shut just when it comes time to make an ID. In the absence of song or call, even many expert birders give up on classifying these elusive look-alikes.
Five species of Empidonax flycatchers are associated with eastern North America. The Least Flycatcher (E. minimus) is, as its name suggests, the smallest of the eastern group, although differences in size are often too subtle to be diagnostic. The Alder Flycatcher (E. alnorum) and the Willow Flycatcher (E. traillii) were considered to be one species, the Traill’s Flycatcher, until just 1973. The two, however, have distinct voices and nest types. The Acadian Flycatcher (E. virescens) may not be cajun, but it is a bird of the bayou, usually found at water’s edge. The Yellow-bellied Flycatcher (E. flaviventris) has the most colorful belly of the eastern group, but don’t be mislead; an empid with a yellow belly is not necessarily a yellow-belly. See how baffling this can be?
Least, alder, willow, and even acadian flycatchers can be found in the western regions of the continent. The latter two are not the only recently split siblings in those parts. The Pacific-slope Flycatcher (E. difficilis) and Cordilleran Flycatcher (E. occidentalis) are known collectively as the Western Complex. These birds are distinct from other empids due to their brighter green and yellow coloration, but they are tough to tell from one another. The Gray Flycatcher (E. wrightii), more gray than most, is well-known as a hearty tail pumper. The Dusky Flycatcher (E. oberholseri) may be considered easier to identify by voice than its peers because it is one of the noisiest empids. Hammond’s Flycatcher (E. hammondii) looks a lot like the Dusky, but has longer wings and a shorter, darker bill.
One final North American empid, the Buff-bellied Flycatcher (E. fulvifrons), is easily the least maddening of this genus. Not only is this Mexican species the smallest of all North American Empidonax flycatchers, its rich orange-buff breast distinguishes it clearly from its cousins.
The American Birding Association offers a fantastic online photo quiz that highlights the futility of trying to identify an empid accurately without something like fifty years of experience. My recommendation is to not waste too much time with the photo, but instead to marvel at the explanation of the insanely painstaking detail involved in putting a name to that adorable whiskered face.