On the bottom of the screen, there are four buttons: RED X = Drag a bird here to delete it. Note that you won't be able to get it back after. RANDOM = If you click this, all of the birds that are already existing will be deleted and a number of random birds will appear in different locations. SOUND = Clicking this will randomly change what sound the birds make. PLUS = Click on this to actually summon/create a bird. Once you have birds on-screen, you can drag them around to your liking. Depending on the branch you place them on, they'll make a higher or lower sound.
i think i spent my entire day on this, please acknowledge it EDIT [07/13/17]: WOW. HOLY COW.. this got featured??!??!?!? thank you all so much....! i nearly had a heart attack when i opened scratch and saw 3440 notifications haha I can't reply to every comment, but I really appreciate all of the kind words!!!