Disney brought fawns into the studios, enabling his animators to draw characters with realistic characteristics like their real life counterparts. This process continued with the 1955 classic Lady and the Tramp.
For example, the model for the Tramp was based on a stray. This process was also used when Disney animators brought lions and lion cubs into the studios as references for characters in The Lion King. Some of this footage is on the bonus features of The Lion King DVD.
Real life observation is crucial to making the animated characters as real and believable as possible. Animators are constantly watching how animals and even actors react in situations and bring these reactions into the imagery of the story that all audiences can enjoy.
The most recent example of this is in the animated movie, Frozen. Disney animators brought a reindeer into the studio so they could better understand how their reindeer character, Sven, would look and act in the movie.