To illustrate a point, Chris asked me this thought-provoking question about a simple field mark on a very common bird: the American Robin. I knew the answer, but had to think about it hard. To identify 700 species, I continually study field guides and learn the possibilities of what thrushes could show up in North America- Fieldfare, Redwing, Dusky Thrush, Aztec Thrush... but did I know all of our thrushes to the same degree of detail? How well do I know the common species? Could I pick out a Bicknell's Thrush by sight on migration in early May along the Atlantic coast, instead of making a special trip to New England? Time (and luck) will tell!