Bird Calendars
NOTES FROM NATURE
By Jerry Toll
Field Identification of Fall Empidonax in Nebraska
The Empidonax genus of North American flycatchers are difficult to separate to species for even the most ardent birder. Most of us rely on vocalizations and behavioral quirks to identify them, and when they are quiet, we pass them off as just "Emps."
Ross Silcock, co-author of the soon-to-be-released "Birds of Nebraska," has come up with a key to separate Empidonax in both the eastern and western portions of our state. It is reprinted here from an original posting on NeBirds@rip.physics.unk.edu.
This is a "field key" designed to sort through the expected possibilities using key structural features. Of course all of these features must be seen well to enable an ID to be approached. By the way, this key is no way to ID vagrants.
Look for the following categories:
1. Underbill color (mostly dark, about half dark, tip only dark).
2. Bill size (small to large).
3. Eye-ring boldness (virtually absent to bold).
4. Eye-ring shape (evenly round, tear-dropped to rear).
5. Primary (wing) extension (long or about equal to tertials, medium or about half tertials, short or about a third or less tertials).
Key to (Nebraska) Panhandle, July-September
A. Underbill mostly dark: Hammond's Flycatcher (verify: bill very small, eye-ring bold and tear-dropped to rear, primary extension long, fresh plumage with quite a bit of yellow on flanks).
B. Underbill about half dark: Dusky Flycatcher (verify: bill pointy and straight-sided; eye-ring bold, usually tear-dropped to rear; primary extension medium).
C. Bill tip dark: Gray Flycatcher (verify: bill shaped like Dusky; eye-ring evenly round, medium shaped; primary extension medium; pumps tail like phoebe). Rarest of the western Empids, especially in fall.
D. Underbill all orange
a. Bill small, some dusky below: Least Flycatcher (verify: bill sides bowed out or convex; eye-ring bold, usually evenly rounded but may be tear-dropped; primary extension very short).
b. Bill medium, bold eye-ring: Cordilleran Flycatcher (verify: eye-ring bold, tear-dropped to rear; primary extension medium). Also applies to Pacific Slope Flycatcher.
c. Bill medium, eye-ring weak or absent: Willow Flycatcher (verify: primary extension medium. Includes Alder Flycatcher although some Alders show an even, rounded eye-ring which is still thin.
Key to East (Nebraska) May to September
All have orange underbills and bills about the same size except for Least; much more of a challenge than the panhandle unless vocalizing!
A. Primary extension very short: Least Flycatcher (verify: see above).
B. Primary extension very long: Acadian Flycatcher (verify: eye-ring bold, evenly rounded; bill large).
C. Primary extension medium:
a. Weak eye-ring but usually present: Willow or Alder Flycatcher (separate by call or song).
b. Bold eye-ring, evenly rounded: Yellow-bellied Flycatcher (verify yellow throat in spring.
01/24/08