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Untold billions spent on the world's most advanced and sophisticated surveillance systems yet he's on a rooftop trying to get visual confirmation. Sounds a bit like a PR stunt. There's something totally absurd about this story.
They are much lighter than airplanes with radar and heat signature similar to birds. Even the larger ones might look like several birds flying close in formation on radar.
Large flocks of birds tend to fly together right after sunset when these drones have been seen. So getting a visual maybe the only way to differentiate