A Quantitative Study of the Nocturnal Migration of Birds

The author develops a quantitative method for studying nocturnal bird migration using telescopic observations of the moon to define a cone of observation and correct raw counts for changing sampling volume. Detailed procedures are given for recording apparent flight paths, identifying coordinates, computing sector densities, and deriving net trend densities, illustrated with figures and field forms. Analyses compare hourly density curves, expose directional sampling biases caused by cone geometry, and assess how topography, geographic position, and meteorological conditions shape local and continental migration patterns. The study synthesizes these elements into conclusions about the temporal variation, spatial distribution, and measurement challenges of nocturnal migration.