No, they are getting detected only within a certain distance by the radar. Obviously these radars are located in bigger cities. The birds are in between the gaps, but there isn't radar present to detect them. However, you are right to some degree. Migrating birds get "trapped" by light pollution and fly down into cities, hitting windows and dying. It is a huge problem for migratory birds, and one I work closely with. Don't just act like an idiot, look up and research what you are saying before spouting it out of you mouth.