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Can anyone tell me what this bird is, taken in Napa Valley, CA, in October 2007?

I have no idea what bird this is. It is very small (about chickadee size). It's beak is curved slightly at the end. It's tail is upright. It has the markings like a brown thrust, but it's much smaller I believe than they are. He was very curious and loved the camera. It hopped around a lot on my porch, discovering the bird feeders and the ...