To the categories of Rumsfeldian epistemology we can add the category of "unknown knowns": things we know without knowing that we know them. Yesterday as I approached Evodia, I saw a sparrow feeding on the ground with the White-Throateds and Juncos. All I saw from that distance was the shape and distinct white wingbars (one low and bold, one high and short and thin), but I immediately thought, "hey, the American Tree Sparrow is back". And so it was.
I hadn't known that the wingbars were a good field mark for that sparrow.
I also saw a Rusty Blackbird just west of Azalea Pond:
But I knew right off what that was and why.
P.S. Googling around, I found a nice recent blog post about American Tree Sparrow identification t birdaz.com: http://birdaz.com/blog/2014/02/27/how-many-wing-bars/.