Good lord you're dense.
Yes, it's really bird concentration, but a request from the airport authority is not science, and does nothing to prove that radar repels birds. It doesn't. It also costs nothing to comply with the request.
Yes, there are birds. Yes, the note requests you turn on your radar. However, surely even you can comprehend that a note on an airport diagram isn't even ancedotal evidence that radar repels birds.
Go back to your microsoft sim and seek out some more aircraft accidents, will you?