Joe Kaplan suggested that the bird I labeled “Townsend’s Warbler” (taken during a Memorial Day trip in Fields, OR) may in fact be a Hermit x Townsend’s Warbler (or Heto Warbler). See https://birdmeister.files.wordpress.com/2011/06/townsendswarbler.jpg (here I also rule out Black-throated Green Warbler). He may have a point …
When looking at Hermit Warblers, our eyes are trained to look for hybridization with Townsend’s. Giveaways are yellow on the breast and streaking on the breast. It is relatively easy to detect if the bird has Townsend’s blood in it. There are a good number of hybrids of that type out there, in particular in areas that the birds are known to hybridize (such as the Southern WA Cascades). Only few birds on the other end of the spectrum have been documented. And we just don’t regularly scrutinize every Townsend’s for Hermit genes.
See http://groups.yahoo.com/group/LACoBirds/message/10522 for a possibly similar bird. Dunn & Garrett’s “Warblers” mentions this rare type of Heto Warbler and shows a plate depicting the front half of the bird.
Here are 2 more shots of the bird in question. You can clearly see the slight yellow wash on the breast. Everything else looks Townsend’s to me. Is there enough evidence to call this a Heto Warbler?
One interesting aspect is of course that this bird was seen and photographed in Fields which might be a little off-track in terms of the regular migration path of hybrid Hermit x Townsend’s Warblers.