How to remove bird droppings from woven patio furniture?
I think I would stay away from soaps that suds up a lot since it will make rinsing more difficult.  A general around-the-house cleaner should do the trick just fine - you can even use a mixture of vinegar and water.

The sooner you clean it off the better as bird droppings tend to eat away at materials over time (they will even etch car paint!)