This radar image from May 16, 1999, captures the distribution of birds in the airspace shortly after the onset of nocturnal migration near Lakes Erie (left) and Ontario (right). Colors represent logarithmic differences in migrant density; in order of lowest to highest density they are green, yellow, orange, red, and purple. Voids in the radar echo pattern occur over the lakes because most of the migrants are landbirds. Radar echoes caused by northbound migrants can be seen extending over the southern portion of both lakes as birds depart the coastal landscape and fly out over the water. Regions of stronger radar echo this early in the migratory flight show where in the landscape (stopover habitat) birds occurred in high densities prior to the onset of migration.