On the way to Oreburgh City, Ash is training Starly so that it will learn Aerial Ace. During the training they meet a girl named Rosebay whos job is to protect the wild Pokemon in the valley. She has noticed that the population of bird Pokemon has decreased over the last copule of days. In turns out that this is all a plan by Team Rocket, who is capturing them inside of an underground base. When Starly winds up in this trap, he tries to rally the Pokemon into trying to break free. (thetvdb.com)