Looks like my batting average is almost improving. One out of three. That does not look like my other Vesper Sparrows, though. I know... no two look alike, and then they change clothes, and look totally different yet again. I will go back and try study on it again, see if I can visualize it as a Vesper Sparrow. It didn't look exactly like a Song Sparrow, to me, either, but after comparing pictures, descriptions, going back and forth until I was totally confused, I ended up filing it as a Song. A Wrong Song, I guess.
OK, I'd say that looks good for OC warbler. The nuthatch is one bird that's easy to ID by it's behavior. They are head-down more often than not, and are usually quite tolerant of close proximity to people. They'll hang around feeders a lot, spend a lot of time on tree trunks, and have a distinct call that they use quite often.
Vireos, on the other hand, spend a lot of time in the canopy, around and among the leaves. They are usually much more difficult to see than nuthatches.
This one was on one feeder for a half second, until another bird flew by, whereupon it flew up and hid under the leaves, then flew to the other feeder, where it stayed just long enough for me to snap this picture before hiding in the grape vines. First time I have seen it here was this morning. If it hangs around long enough, I will try to observe behavior, and see if it makes any sounds.