I do not know of any waterless products that I would trust. Mild soap and water is the best. Usually even just plain water will work just fine. If you get at it right away while it is still fresh and wet, a soft paper towel will get it done.
Depending on the kind of bird and what they were eating, some of those droppings can etch the paint if left on long enough where you will need to buff it out after cleaning the mess.