After some pictures were posted on Facebook, we decided to chase an Olive Sparrow that has been frequenting one of the bird blinds at South Llano River State Park. This bird is normally seen in South Texas, especially in the Rio Grande Valley. Here is a map of the sightings recorded on eBird.org - the yellow circle is the state park. This is the furthest north that the species has been recorded and it has been seen there on multiple occasions.
We decided to do this as a day trip, leaving Georgetown a bit after 6AM and arriving just at 9AM. This park has four bird blinds. They all have well designed features for the birds to forage around but are all very frustrating for photography. The viewing huts have windows (which you can't photograph through) and no good places for setting up a camera-tripod. Complaining aside, we headed over to the Agarita Blind and settled in.
We got our first glimpse of the sparrow soon after. This type of sparrow behaves much like a Towhee, foraging on the ground in the undergrowth at the edge of the clearing. During our 6 hour vigil, we saw it a half dozen times but it never came out in the open for more than a few seconds. From the posted pictures, others had had more luck with the bird perching on one of the decorative stumps.
We did manage to get a couple of photos that show the field marks. The Olive Sparrow is a medium sized sparrow with a very low contrast body with no patterning on the back or wings. It has a light gray breast and a pale olive wash on its gray back and wings. This is the only sparrow with this olive coloration so it is a pretty distinctive marking. The head has two narrow rufous crown and eye stripes and a broken white eye ring around a red eye. All in all, it looks more like a miniature, pale Green-Tailed Towhee than it does a sparrow.