Tweeters,

Yellow-rumped Warblers at this season (when many are in drab dress) are
readily identified by voice. The chip note of a Myrtle's Yellow-rumped is
recognizably different from the call of an Audubon's. To my ear, the
Mrytle call has a metallic ring. The Audubon's call lacks this sharp edge.

It's too bad that birders in the western U.S. don't have the diversity or
abundance of warblers that those in the eastern U.S. have to gain more
experience with warbler chips. Last May I birded Manitoba with "eastern"
experts Michael O'Brien and Ned Brinkley on the WINGS southern Manitoba
tour. In a short week, I observed both leaders identify many individuals by
their call notes, even though this was the height of the singing season.
With (much) experience, I observed many are routinely identified by their
call notes, even migrants overhead at night! There are a few troublesome
groups, especially the Blackpoll/Bay-breasted.

In Washington, I have the most trouble with Nashville/Orange-crowned notes
which sound similar to my ear; otherwise I believe most of our warblers can
be identified by their chips (daytime notes anyways, migrants at night I'm
still fuzzy on).

Andy Stepniewski
Wapato WA