Although interested generally in geographical distribution and natural history of vertebrates, his major activities concerned birds. Associated officially with the U. S. Biological survey in the economic aspects of ornithology and mammalogy, his extra-curricular interests embraced membership in many related societies. Once president of the American Ornithologists' Union, and earlier the Chairman of its Committee on Migration, much of this correspondence deals with affairs of that organization.

With the letters are scattered news clippings and lists of species observed as a “bird watcher.” While the majority are written to Witmer Stone a small number are addressed to other ornithologists.

The subjects covered include taxonomic matters, type specimens in the Academy's collection, distributional memoranda sent in letters posted from many parts of the U. S., and biographical information about ornithologists met on his travels.