Short Stories from Hogwarts of Heroism, Hardship and Dangerous Hobbies (Pottermore Presents, #1)

by J.K. Rowling

The animal into which one turns, if an Animagus, seems always to be that which becomes the Patronus. There is no known instance of the Animagus form changing to match the Patronus if the latter changes, but the Animagus who can also produce a Patronus is highly unusual and no study has ever been done on sufficient numbers to draw firm conclusions.