"Perri is a 1957 film from Walt Disney Productions, based on Felix Salten's 1938 Perri: The Youth of a Squirrel"

Wikipedia:

In the 1982 CBC television documentary Cruel Camera (produced by The Fifth Estate) Roy O. Disney, who was a cameraman on Perri's "fenced in" forest set, describes the film as both misrepresenting nature and being cruel to animals. Disney says, "Well, you just aren't going to go out into the woods and set up a camera and wait for the squirrel to come." He explains that the film used a cast of twenty tamed squirrels and "a lot" of wild ones, which were considered "expendable." Disney tells of one particular scene involving a chase with a marten, the film's "arch-villain." In the scene, one squirrel is eaten by the marten, however Disney says that in order to film the scene, they had to sacrifice a "number of squirrels." Practically speaking, "they found a very simple way to film the heroine narrowly escaping predators: just film her not narrowly escaping at all, shout cut, then call for a fresh Perri."