The best strategy for Birdday Party (Birthday Party) level 18-6 is to fire the Blue bird horizontally, splitting to do as much damage to the left tower as possible. The majority of the tower should topple to the left. Use the next Blue bird horizontally again, destroying some of the ice from the middle structure and clearing a path for the last Blue bird. With this bird, take out the bottom-left of the right tower. It should topple to the left and destroy all remaining pigs. The score in the video below is 96,140.