From Bulbapedia, the community-driven Pokémon encyclopedia.
Rosebay (Japanese: ユカリ Yukari) is a Pokémornithologist, and the character of the day in A Staravia is Born!.
Rosebay acted as a sort of Pokémon Ranger. Her job was to keep track of all the Pokémon inhabiting a forest that Ash and his friends happened to be passing through on their way to Oreburgh City. She introduced herself to them and Brock quickly flirted with her before being dragged away by his Croagunk. Rosebay invited the group along on her hike to look for bird Pokémon. She first took them to a Swablu nest and noticed that the Swablu were gone, which prompted her to recall that a lot of bird Pokémon went missing recently.
It is soon discovered that Team Rocket set up a giant net in a gorge to trap the bird Pokémon. Ash's Starly helps rescue the Pokémon, evolving into Staravia in the process, and defeating Team Rocket. Rosebay thanked Staravia for its help and told Ash and his friends that the Pokémon were safe once more.