Audubon's Warbler

I took advantage of my current unemployment this morning and spent about 2.5 hours birding the neighborhood. This morning was very cold, but very clear without much wind. I didn't start until 10:00 AM but I don't think I missed much early morning bird activity because of the temperature. The most interesting bird I found was this Audubon's Warbler:

Audubon's Warbler is a subspecies of Yellow-rumped Warbler, the most common kind of warbler in central Texas during the winter. Audubon's is a western subspecies that usually does not occur east of the trans-pecos region. The much more common subspecies of Yellow-rumped Warbler in Austin (and most of Texas) is Myrtle Warbler. The most obvious difference between Myrtle and Audubon's is the color of the throat. Myrtle has a white throat and Audubon's has a yellow throat. My photo shows a couple additional differences:

1. The auricular region is much less distinct from the rest of the face. Myrtle Warblers have a clear border between the darker auricular region and the lighter throat that extents to the edge of the nape. (Click on the photo above and see the note I added to the photo on Flickr that marks the auricular region of the face.) 
2. Myrtle warblers have a pale supercilium and more distinct dark horizontal line through their eye.

Many birders get tired of seeing Yellow-rumped Warblers in the winter because they are so common. We yearn to find something else. But it's always worth closely inspecting even the common birds. The better you learn them, the more obvious subtle differences will be to you!