The yellow-bellied flycatcher and least flycatcher are two similar-looking species of small songbirds found in North America. They belong to the genus Empidonax, a group of birds known as “empid” flycatchers. These two empids can be very challenging to tell apart by sight or sound. Careful observation of differences in appearance, voice, habitat, and range are needed to properly identify them. This article will go over the key identification points, ecology, and taxonomy to distinguish these oft-confused flycatchers.
How to Identify Yellow-bellied and Least Flycatchers
Appearance
At first glance, yellow-bellied and least flycatchers look nearly identical. They are both small, drab empid flycatchers with olive to gray-brown upperparts, light underparts, eyerings, and double wingbars. However, there are some subtle differences in plumage and structure.
The yellow-bellied flycatcher is slightly larger and chunkier than the lean least flycatcher. It has a larger head and bill and a more upright posture when perched. Its plumage tones also tend to be more olive-brown compared to the grayer least flycatcher. The yellow-bellied shows faint yellowish wash on its underparts, most noticeable on the throat and breast (its namesake). The yellowish tinge is usually absent in least flycatchers.
When it comes to wingbars, the yellow-bellied has narrow, indistinct bars while the least’s bars are bright and prominent. The yellow-bellied also has longer primary projection beyond the tertials. When perched, its wings extend farther beyond the tail compared to the shorter wings of the least flycatcher.
Voice
Listen for the birds’ vocalizations. Yellow-bellied flycatchers have a loud, ringing “che-bek!” call. By comparison, least flycatchers make a softer “che-bec” call. The yellow-bellied’s voice has a burry or buzzy quality while the least’s voice is higher-pitched and sharper.
The most reliable way to identify an unknown empid flycatcher is to hear one give its song. Yellow-bellied flycatchers sing a recognizable “pee-ah-wee” song. Least flycatchers have a faster “che-bek, che-bek…” song sounding almost like a squeaky wheelbarrow. Learning these diagnostic songs by listening to recordings is extremely helpful for identification.
Behavior
Observing behavior can provide more clues to tell these species apart. Yellow-bellied flycatchers are more active than least flycatchers, displaying more spreading of the tail and flicking of the wings while perched. When pursuing insects, yellow-bellied sally from branches to catch prey in flight in a flycatcher fashion, while least flycatchers tend to glean prey from foliage in a vireo or warbler-like manner.
Habitat
These species can be found in slightly different woodland habitats during the breeding season. Yellow-bellied flycatchers favor wetter areas like swampy thickets and the edges of streams or ponds. Least flycatchers occupy drier woods often at higher elevations. This habitat preference reflects their slightly different nesting sites. Yellow-bellied nests are usually close to the ground near water while least flycatchers nest higher up in trees.
During migration, both occur along woodland edges or open areas with scattered trees. They also turn up on migration together in second-growth clearings and early successional habitats. Outside of the breeding grounds,habitat can’t reliably separate the two.
Range
Their breeding and non-breeding distributions can help distinguish yellow-bellied flycatchers from least flycatchers. Yellow-bellied flycatchers breed across Canada and the northern United States, from Alaska to central New England. Least flycatchers have a more southerly breeding distribution, ranging from the Pacific Northwest through the central and southern U.S. east of the Great Plains.
On migration and in winter, yellow-bellied flycatchers occur mainly along the east and Gulf coasts in the southeastern U.S., rare and local inland. Least flycatchers are widespread over much of eastern North America on migration. Their wintering grounds center across Central America, extending into northern South America. Know the expected species for your region.
Table Comparing Field Marks
| Trait | Yellow-bellied Flycatcher | Least Flycatcher |
|---|---|---|
| Size | Larger, chunkier | Smaller, leaner |
| Bill | Bigger | More petite |
| Plumage Tone | Olive-brown | Gray-brown |
| Underparts | Yellowish wash | No yellowish |
| Wingbars | Indistinct, thin | Bold, prominent |
| Primary Projection | Longer | Shorter |
| Call | “che-bek!” buzzy | “che-bec” higher pitched |
| Song | “pee-ah-wee” | “che-bek, che-bek…” |
| Behavior | More active, flycatching | Less active, gleaning |
| Habitat | Wet woods, near water | Drier upland woods |
| Breeding Range | Northern U.S. and Canada | Central and southern U.S. |
Taxonomy and Classification
Both yellow-bellied and least flycatchers belong to the large family Tyrannidae, the tyrant flycatchers. This exclusively New World family contains over 400 species. They are the dominant group of suboscine passerines found in North and South America.
Within Tyrannidae, the yellow-bellied and least flycatchers are placed in the genus Empidonax. This challenging genus contains several similar species known as “empidonax” flycatchers. The genus name Empidonax comes from the Greek words empis meaning “gnat” and anax meaning “master”. This refers to their specialized insectivorous habits.
Prior to 1973, the yellow-bellied and least flycatchers were considered to be just one species – Traill’s flycatcher. The discovery of differences in morphology, vocalizations, habitat, and hybridization rates prompted scientists to split them into separate species. They were split along with several other empidonax flycatchers at that time.
Some taxonomic authorities still place them in the single species Empidonax traillii. But most now recognize the yellow-bellied flycatcher and least flycatcher as distinct species:
- Yellow-bellied flycatcher – Empidonax flaviventris
- Least flycatcher – Empidonax minimus
These two empidonax flycatchers are not closely related within the genus. Based on DNA evidence, yellow-bellied flycatchers belong to a clade with other pond-breeding empids like acadian flycatcher. Least flycatchers are in a separate clade with empids that breed in more open and dry habitats. This aligns with differences observed in their ecology and vocalizations.
Ecology and Behavior
Let’s take a closer look at some aspects of the breeding ecology and behavior that set yellow-bellied and least flycatchers apart from each other:
Breeding Habitat
The yellow-bellied flycatcher nests in wet, swampy woods, especially areas dominated by conifers like Atlantic white cedar, tamarack, and black spruce. They are often found around beaver ponds, oxbow lakes, and bogs. Least flycatchers favor drier, more open deciduous woodlands, with maples, aspens, and birches. They also use parks, orchards, and shade trees in rural areas.
Nest Placement
As suited for their damp habitat, yellow-bellied flycatchers build open cup nests low in conifers, usually only 1-3 meters above ground. Least flycatchers nest much higher up, averaging around 8 meters up in deciduous trees.
Breeding Range
The breeding distribution of yellow-bellied flycatchers is centered across Canada, Alaska, and the northern border of the continental US, extending south at higher elevations. Least flycatchers breed at lower latitudes, throughout the central and eastern United States south of Canada. Their breeding ranges only minimally overlap in the northern Midwest and southern Canada.
Migration
In fall, yellow-bellied flycatchers migrate earlier, beginning southbound migration in July. Least flycatchers start migrating later, mainly during August and September. On the wintering grounds, yellow-bellied flycatchers largely occupy coastal areas in the southeastern US and Caribbean. Least flycatchers have a much broader winter distribution extending from Mexico through Central America into northern South America.
Foraging and Feeding
The yellow-bellied flycatcher actively sallies and hawksnatches flying insects on the wing. The least flycatcher does this as well but also gleans insects from foliage in a more sit-and-wait manner. Studies have found yellow-bellied flycatchers consume a higher proportion of flying insects like flies and bees, while least flycatchers eat more caterpillars.
Hybridization
In the narrow zone where their breeding ranges overlap, yellow-bellied and least flycatchers occasionally hybridize. However, hybridization rates are quite low, estimated at only around 2%. This reproductive isolation supports their status as two separate species. Where they co-occur, competition for habitat and resources may help keep the species segregated.
Conclusion
In summary, yellow-bellied and least flycatchers can be tricky to distinguish by sight due to their similar plumages. A combination of subtle differences in size, plumage tones, wingbars, vocalizations, habitat preferences, and behavior are needed to confidently identify them. Listen especially for their distinctive call notes and breeding songs. Learn the species’ respective ranges and preferred breeding habitats. Careful study and experience in the field will help sharpen identification skills and prevent confusing these two empidonax species. Just take your time watching and listening closely when encountering these look-alike flycatchers!
