Before the first Happy Feet movie was released, Mumble was rumored to loose his juvenile feathers when he jumped off the ice cliff to stop the aliens from taking the fish. However, this got scrapped before the final cut of the film. However, the books Chillin' With Mumble, Happy Feet: The Essential Guide, and Happy Feet: The Movie Storybook depict Mumble with his full adult plumage.
In the conclusion of the book, Mumble is seen without his juvenile feathers.
Mumble is first seen without his juvenile feathers when he is in the aquarium. He is also seen molted when he comes back to Emperor-Land.
Mumble molts when he jumps off the ice cliff. More pictures of him with his adult feathers might have been copied from Happy Feet: The Essential Guide. At the end of the book, he is seen with his adult plumage in a yellow background.
- In Happy Feet Two, his baby feathers have grown back but it's unknown if Mumble will have his adult feathers in Happy Feet Three.