Professionalization within the sciences has often been presented as a process of separation between scientists and the public. Implicit within this conception of professionalization is a hierarchical conception of knowledge which is diffused from the laboratory to the public. However, the history of ornithology reveals very different dynamics which requires historians to challenge this notion of professionalization. From its origins as a science oriented toward the collection of specimens for the purposes of taxonomy, ornithologists have formed a community of practice with amateurs. Amateur bird watching fostered a new set of skills for bird identification at a time when professional ornithologists became reliant upon such skills in order to study birds in the field. A study of the Cornell Laboratory of Ornithology reveals the extent to which professional ornithologists were embedded within the community of bird watchers and depended upon them for the very survival of the institution. The interaction between professional ornithologists and a wider culture of bird watchers as seen through the recording activity of the CLO is inadequately explained by models the isolate “science” and the “public” and assume a one-way flow of scientific knowledge. The example of sound recording shows how amateurs were important figures in scientific networks which were maintained by personal relationships. The rise of citizen science at the CLO in the late 1980s demonstrates its reliance upon the participation of large numbers of amateur bird watchers to produce data published in scientific literature. Rather than a diffusionist model of professionalization, the Cornell Laboratory of Ornithology points to a model of professionalization through popularization built upon a common culture of bird watching.