in 1920, lincoln joined the u.s. bureau of biological survey (at the time, a unit of the united states department of agriculture, and now part of the united states fish and wildlife service ) and was given the task of organizing and expanding the bird banding program nationwide. the migratory bird treaty act of 1918 had established federal responsibility for migratory birds; the result was that the north american bird banding program took the place of earlier smaller-scale efforts by individuals and the short-lived american bird banding association. during the period of his tenure, 1920–1946, lincoln was highly influential: he improved methods for trapping and banding, developed record-keeping procedures, recruited banders, fostered international cooperation, and promoted banding as a tool for research and wildlife management. he proposed a means to estimate the continent-wide population size of a bird species, using reports from hunters and counting "returns" (birds killed that are wearing bands); this metric became known as the lincoln index. he developed the flyway concept, a key idea in the management and regulation of hunting of migratory birds.