"Timmy Tiptoes" is unique amongst Potter's children's books: it is the only one depicting American mammals. The title character is an eastern grey squirrel, a species exported from America to Britain, and flourishing there around 1900. It was unlikely Potter saw the animals in the woods around Hill Top as they had yet to become established in the Lake District. She probably relied for models on specimens in the Small Mammal House of a zoo, and consulted reference works in the library of the Natural History Museum to aid her work.