A new discovery is fun. I met up with another birder who was feeding the little birds. Suddenly she said, "Look, see that little bird with the red head. Take a picture! Take a picture!" At first I thought she may have seen a male purple finch. Finally I saw the bird she was watching and had no idea what it was other than a sparrow, and not red-headed, more russet. There are sparrows and there are sparrows and they're all different. This sparrow was shy, coming in for a nut bit, then hiding, not at all aggressive like the house sparrows. I had no idea which sparrow it was, so took lots of pictures to match up with bird book images. Over by the big field I met two other birders, serious, know-everything birders. I showed them the pictures. "What's this?" Fast answer, "Chipping sparrow", also known as Chippie. But I've checked with the bird book and another expert. It's not a "chippie". It's an American Tree Sparrow.