You should use a gentle detergent such as Dawn Dish Soap or Fairy Liquid Washing Up Liquid. If you use either of these two solutions, you should only use a small amount. Also, you need to completely wash the soap out of the feathers and thoroughly dry the bird. Place the bird inside and allow him to replace his natural oil in his feathers while preening. He should remain indoors for one to two days. If you do not have either of these two soaps then just rinse him with water and allow him to dry indoors for a couple of hours. On another note, he could actually choke and die he if gets stuck in the mud. The Regal Swan