I initially bought iBird Pro in one of its earlier versions for one reason and one reason only. Bird vocalizations. If I was going out looking for a rarity or even just for a bird that I hadn’t seen (or heard) in awhile I would play the songs and, especially, the chip notes prior to getting into the field to ensure that if the bird called I would recognize it. And, sometimes, I use chip notes to try to lure a bird in, using just a couple of notes and only if I was sure it would not be interfering with a breeding bird or other birder’s enjoyment. After all, I don’t want to bring down the wrath of the number one birder in the world.