What animal Grain Rain changed his clothes for the first time?

Animals are birds. "Grain Rain changed clothes for the first time" comes from Wuyun Bridge written by Lu You in Song Dynasty: Grain Rain changed clothes for the first time, and roses fell in the garden. The singing pigeon is far away, and the swallow flies alone. The "singing pigeon" and "swallow" in the works correspond to the extension of the first two sentences, both of which are birds and beasts.