Thursday, May 27, 2010

Empidonax Flycatchers

Least Flycatcher

"Traill's" Flycatcher

On Wednesday the mosquitoes were out in force and I caught two Empidonax Flycatchers.  The genus Empidonax contains several of the most similar birds in North America--unless the birds are singing. They almost never sing while they are being banded.

The Least Flycatcher above can be told from the "Traill's" Flycatcher below because the Least is somewhat smaller and its bill is slightly shorter and stubbier.  Hard to tell in my photos, but the Least's eyering is usually wider and more complete.  In the field, the Least Flycatcher sings, "Che-bick!"

The "Traill's" is in quotes, because this name no longer refers to a species.  The old Traill's Flycatcher has been split into Alder and Willow Flycatchers.  Alder Flycatchers, who sing "fee-bee-o!", or, sometimes "free beer!," are found further north than are Willows, who sing "Fitz-bew."  Where their ranges overlap, the two forms do not interbreed, hence they are recognized as separate species.

When not singing, these two species are almost impossible to tell apart. Many bird books suggest that Alder Flycatchers have greener backs than the browner backed Willow Flycatcher.  If this field mark is valid, then my "Traill's" is probably an Alder Flycatcher.  (I have heard Alder Flycatchers singing in the summer in the eastern half of the nearby Cannon River Wilderness Area.)  Last year, however, when I sent the Bird Banding Laboratory a photo of a hand-held flycatcher that clearly showed a bird with a greenish tint to the back, they replied that a quiet bird, conservatively, is always a "Traill's" Flycatcher.

Just to make matters more confusing, two other Empidonax flycatchers are found in Minnesota, the rare Acadian Flycatcher (rare, at least, here) and the fairly common migrant, and fairly distinctive, Yellow-bellied Flycatcher.  Acadians sing "Pee-tsup" while Yellow-bellied Flycachers have a fairly distinctive yellow throat (and belly).  At least a half-dozen additional species in the genus Empidonax are found in western North America...

2 comments:

  1. Hi Dan - I thought the Cannon River (east side) had Acadian flycatchers (based on song). I have seen him twice near the footbridge this year.

    When was the last time you heard(saw) the alder flycatcher there?

    Larry S

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  2. The Acadian Flycatchers are in the woods in the first part of the hiking trail. The Alder Flycatcher is in the swampy area at the far end of the trail.

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