I just came cross these products called bird bath spray, which is a chemical used to clean the birds. That reminded me when I had a few birds almost two decades ago, they never ever took a single bath or shower for years. I never cleaned them. They seemed to be able to clean their own feather every day with their mouths.
Years ago someone told me his bird would take a bath on his own if he put a bowl of water in the cage.
I believe some birds in the wild can't take bath in natural body of water such as a river or a lake, because they can't swim. It is also hard to imagine how they would want to get wet. I heard birds have body temperature of over 50% higher than humans. Being wet can be very energy consuming for them if they don't freeze to death.
Do birds require to take bath at all?
How do you bath them? Or clean them?
How do you bath a bird? 
I never cleaned them. They seemed to be able to clean their own feather every day with their mouths. 
