I felt lucky that this Yellow-rumped Warbler posed along the boardwalk close enough for an uncropped image. These common warblers are usually very jumpy and digiscoping is not a very practical method to capture them.
This white-throated bird is a member of the "Coronata group" formerly regarded as a separate species (Myrtle Warbler) from the "Auduboni group" formerly known as Audubon's Warbler which has a yellow throat.
The Coronata group is further divided into two subspecies D. c. coronata breeding over most of Eastern North America and the larger more heavily streaked D. c. hooveri breeding from Alaska and NW Canada. Both subspecies have been collected in Texas in winter but I don't think they are distinguishable in the field and I cannot be sure which one this is.
Olympus D-550z / Nikon FieldScope 3 / 30XWA (hand-held - no adapter).