Ken, one way I distinguish the Audubon and Myrtle forms is by the shape of
the throat patch, an approach that is helpful throughout the year. I think
of the Myrtle showing the throat patch flaring out and upward toward the
auricular area, and the Audubon throat patch more vertically aimed toward
the breast or underwing coverts.
Recently I observed a bird with a bright white throat patch (Myrtle-y), and
in the shape of the Audubon throat patch.

The National Geographic field guide also shows the Myrtle with a whitish
supercilium,though that field mark might not always be visible.
Your photos show yellow/white in the (Audubon-shaped) throat patch,
suggesting an intergrade condition. And one of those birds has a distinct
white supercillium
Others may know of different distinguishing field marks. Birds of the World
goes into a number of subtleties.

Dan McDougall-Treacy

On Thu, May 26, 2022 at 3:15 PM Kenneth Trease <krtrease at gmail.com> wrote:


> I recently returned from a trip to south-central Oregon. I photographed

> two different Yellow-rumped Warblers (YRWA) that I thought might be

> intergrades as they seem to have some characteristics of both Audubon's and

> Myrtle forms. I would be interested to hear other's opinions-intergrades

> or just within the normal variation for this species? Here is a link to

> the photos on Flickr:

>

> https://www.flickr.com/photos/cavuken/albums/72177720299278430

>

> _______________________________________________

> Tweeters mailing list

> Tweeters at u.washington.edu

> http://mailman11.u.washington.edu/mailman/listinfo/tweeters

>