Radar Ornithology and the Conservation of Migratory Birds

It is possible to study with surveillance radar the movements of migrating birds in the atmosphere at different spatial scales. At a spatial scale within a range of 6 kilometers, high-resolution, 3-centimeter wavelength surveillance radar (e.g. BIRDRAD) can detect the departure of migrants from different types of habitat within a few kilometers of the radar. The radar operator can also sample the flight speeds of targets in an attempt to classify birds by their velocity. At a larger spatial scale (10-60 kilometers), Doppler weather surveillance radar (WSR-88D) can be used to measure the density of birds in the radar beam as they begin a migratory movement (exodus) within 60 kilometers of the radar. Within minutes of the onset of nocturnal migration, the distribution and density of echoes in the radar beam can provide information on the geographical sources of migrants on the ground (migration stopover areas), and satellite imagery can be used to identify the topography and habitat type that characterizes these areas. At a continental scale, the national network of WSR-88D radars can be used to monitor bird migration over the United States on an hourly basis at different altitudes dependent on distance from the radar. The latter achievement is significant because it provides a means of monitoring the season-to-season and year-to-year variation in the patterns of migration at different altitudes for different geographical regions and the nation as a whole.