The difficult sparrows are Lark, Clay-colored, Vesper and Lincoln's. They aren't really difficult. They are just required for the stupid contest. Good news. I have all of them. The last one that I needed was Vesper. I was getting worried but we saw 2 of them this weekend. It has become apparent that they are difficult to photograph. I do not have a photo to share with you. I do have photos of some of the other sparrows.
WARNING - they all look alike. Don't be shocked when you can't tell the difference between any of these.