What is your favorite animal movie of all time ?

I am sure that most of us started out with something like "Bambi" as our favorite animal character movie, and there are also all of the cartoon characters, like Mickey Mouse and Donald Duck that we loved as children.
Sometimes, there are movies that touch our hearts, even as an adult. One of my all-time favorites is another Walt Disney classic, Old Yeller. It is about a boy and his wonderful dog, who (sadly) gets rabies and has to be put down at the end of the movie.
Another one that I really loved; but with a much happier ending, was "The Black Stallion" , which is made from the Black Stallion series of books by Walter Farley.

"Turner and Hootch", about a Mastiff whose owner is murdered, is also one that I have enjoyed wating over and over.
What are some other favorite moves about animals ?